Jersey project is built using Apache Maven software project build and management tool. All modules produced as part of Jersey project build are pushed to the Central Maven Repository. Therefore it is very convenient to work with Jersey for any Maven-based project as all the released (non-SNAPSHOT) Jersey dependencies are readily available without a need to configure a special maven repository to consume the Jersey modules.

<snapshotRepository>
    <id>ossrh</id>
    <name>Sonatype Nexus Snapshots</name>
    <url>https://jakarta.oss.sonatype.org/content/repositories/snapshots/</url>
</snapshotRepository>

Since starting from a Maven project is the most convenient way for working with Jersey, let's now have a look at this approach. We will now create a new Jersey project that runs on top of a Grizzly container. We will use a Jersey-provided maven archetype. To create the project, execute the following Maven command in the directory where the new project should reside:

mvn archetype:generate -DarchetypeArtifactId=jersey-quickstart-grizzly2 \
-DarchetypeGroupId=org.glassfish.jersey.archetypes -DinteractiveMode=false \
-DgroupId=com.example -DartifactId=simple-service -Dpackage=com.example \
-DarchetypeVersion=2.38-SNAPSHOT

Feel free to adjust the groupId, package and/or artifactId of your new project. Alternatively, you can change it by updating the new project pom.xml once it gets generated.

Once the project generation from a Jersey maven archetype is successfully finished, you should see the new simple-service project directory created in your current location. The directory contains a standard Maven project structure:

There are 2 classes in the project source directory in the com.example package. The Main class is responsible for bootstrapping the Grizzly container as well as configuring and deploying the project's JAX-RS application to the container. Another class in the same package is MyResource class, that contains implementation of a simple JAX-RS resource. It looks like this:

package com.example;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;
import javax.ws.rs.core.MediaType;

/**
 * Root resource (exposed at "myresource" path)
 */
@Path("myresource")
public class MyResource {

    /**
     * Method handling HTTP GET requests. The returned object will be sent
     * to the client as "text/plain" media type.
     *
     * @return String that will be returned as a text/plain response.
     */
    @GET
    @Produces(MediaType.TEXT_PLAIN)
    public String getIt() {
        return "Got it!";
    }
}

A JAX-RS resource is an annotated POJO that provides so-called resource methods that are able to handle HTTP requests for URI paths that the resource is bound to. See Chapter 3, JAX-RS Application, Resources and Sub-Resources for a complete guide to JAX-RS resources. In our case, the resource exposes a single resource method that is able to handle HTTP GET requests, is bound to /myresource URI path and can produce responses with response message content represented in "text/plain" media type. In this version, the resource returns the same "Got it!" response to all client requests.

The last piece of code that has been generated in this skeleton project is a MyResourceTest unit test class that is located in the same com.example package as the MyResource class, however, this unit test class is placed into the maven project test source directory src/test/java (certain code comments and JUnit imports have been excluded for brevity):

package com.example;

import javax.ws.rs.client.Client;
import javax.ws.rs.client.ClientBuilder;
import javax.ws.rs.client.WebTarget;

import org.glassfish.grizzly.http.server.HttpServer;

...

public class MyResourceTest {

    private HttpServer server;
    private WebTarget target;

    @BeforeEach
    public void setUp() throws Exception {
        server = Main.startServer();

        Client c = ClientBuilder.newClient();
        target = c.target(Main.BASE_URI);
    }

    @AfterEach
    public void tearDown() throws Exception {
        server.stop();
    }

    /**
     * Test to see that the message "Got it!" is sent in the response.
     */
    @Test
    public void testGetIt() {
        String responseMsg = target.path("myresource").request().get(String.class);
        assertEquals("Got it!", responseMsg);
    }
}

In this unit test, a Grizzly container is first started and server application is deployed in the test setUp() method by a static call to Main.startServer(). Next, JAX-RS client components are created in the same test set-up method. First a new JAX-RS client instance c is built and then a JAX-RS web target component pointing to the context root of our application deployed at http://localhost:8080/myapp/ (a value of Main.BASE_URI constant) is stored into a target field of the unit test class. This field is then used in the actual unit test method (testGetIt()).

In the testGetIt() method a fluent JAX-RS Client API is used to connect to and send a HTTP GET request to the MyResource JAX-RS resource class listening on /myresource URI. As part of the same fluent JAX-RS API method invocation chain, a response is read as a Java String type. On the second line in the test method, the response content string returned from the server is compared with the expected phrase in the test assertion. To learn more about using JAX-RS Client API, please see the Chapter 5, Client API chapter.

Now that we have seen the content of the project, let's try to test-run it. To do this, we need to invoke following command on the command line:

mvn clean test

This will compile the project and run the project unit tests. We should see a similar output that informs about a successful build once the build is finished:

Results :

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  7.519 s
[INFO] Finished at: 2021-01-29T08:16:04+01:00
[INFO] ------------------------------------------------------------------------

Now that we have verified that the project compiles and that the unit test passes, we can execute the application in a standalone mode. To do this, run the following maven command:

mvn exec:java

The application starts and you should soon see the following notification in your console:

May 26, 2013 8:08:45 PM org.glassfish.grizzly.http.server.NetworkListener start
INFO: Started listener bound to [localhost:8080]
Jan 29, 2021 8:33:02 AM org.glassfish.grizzly.http.server.HttpServer start
INFO: [HttpServer] Started.
Jersey app started with WADL available at http://localhost:8080/myapp/application.wadl
Hit enter to stop it...

This informs you that the application has been started and it's WADL descriptor is available at http://localhost:8080/myapp/application.wadl URL. You can retrieve the WADL content by executing a curl http://localhost:8080/myapp/application.wadl command in your console or by typing the WADL URL into your favorite browser. You should get back an XML document in describing your deployed RESTful application in a WADL format. To learn more about working with WADL, check the Chapter 18, WADL Support chapter.

The last thing we should try before concluding this section is to see if we can communicate with our resource deployed at /myresource path. We can again either type the resource URL in the browser or we can use curl:

$ curl http://localhost:8080/myapp/myresource
Got it!

As we can see, the curl command returned with the Got it! message that was sent by our resource. We can also ask curl to provide more information about the response, for example we can let it display all response headers by using the -i switch:

curl -i http://localhost:8080/myapp/myresource
HTTP/1.1 200 OK
Content-Type: text/plain
Content-Length: 7

Got it!

Here we see the whole content of the response message that our Jersey/JAX-RS application returned, including all the HTTP headers. Notice the Content-Type: text/plain header that was derived from the value of @Produces annotation attached to the MyResource class.

In case you want to see even more details about the communication between our curl client and our resource running on Jersey in a Grizzly I/O container, feel free to try other various options and switches that curl provides. For example, this last command will make curl output a lot of additional information about the whole communication:

$ curl -v http://localhost:8080/myapp/myresource
*   Trying 127.0.0.1:8080...
* TCP_NODELAY set
* Connected to localhost (127.0.0.1) port 8080 (#0)
> GET /myapp/myresource HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.68.0
> Accept: */*
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 200 OK
< Content-Type: text/plain
< Content-Length: 7
<
* Connection #0 to host localhost left intact
Got it!

To create a Web Application that can be packaged as WAR and deployed in a Servlet container follow a similar process to the one described in Section 1.1, “Creating a New Project from Maven Archetype”. In addition to the Grizzly-based archetype, Jersey provides also a Maven archetype for creating web application skeletons. To create the new web application skeleton project, execute the following Maven command in the directory where the new project should reside:

mvn archetype:generate -DarchetypeArtifactId=jersey-quickstart-webapp \
                -DarchetypeGroupId=org.glassfish.jersey.archetypes -DinteractiveMode=false \
                -DgroupId=com.example -DartifactId=simple-service-webapp -Dpackage=com.example \
                -DarchetypeVersion=2.38-SNAPSHOT

As with the Grizzly based project, feel free to adjust the groupId, package and/or artifactId of your new web application project. Alternatively, you can change it by updating the new project pom.xml once it gets generated.

Once the project generation from a Jersey maven archetype is successfully finished, you should see the new simple-service-webapp project directory created in your current location. The directory contains a standard Maven project structure, similar to the simple-service project content we have seen earlier, except it is extended with an additional web application specific content:

The project contains the same MyResouce JAX-RS resource class. It does not contain any unit tests as well as it does not contain a Main class that was used to setup Grizzly container in the previous project. Instead, it contains the standard Java EE web application web.xml deployment descriptor under src/main/webapp/WEB-INF. The last component in the project is an index.jsp page that serves as a client for the MyResource resource class that is packaged and deployed with the application.

To compile and package the application into a WAR, invoke the following maven command in your console:

mvn clean package

A successful build output will produce an output similar to the one below:

Results :

Tests run: 0, Failures: 0, Errors: 0, Skipped: 0

[INFO]
[INFO] --- maven-war-plugin:2.2:war (default-war) @ simple-service-webapp ---
[INFO] Packaging webapp
[INFO] Assembling webapp [simple-service-webapp] in [.../simple-service-webapp/target/simple-service-webapp]
[INFO] Processing war project
[INFO] Copying webapp resources [.../simple-service-webapp/src/main/webapp]
[INFO] Webapp assembled in [110 msecs]
[INFO] Building war: .../simple-service-webapp/target/simple-service-webapp.war
[INFO] WEB-INF/web.xml already added, skipping
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  4.520 s
[INFO] Finished at: 2021-01-29T08:42:11+01:00
[INFO] ------------------------------------------------------------------------

Now you are ready to take the packaged WAR (located under ./target/simple-service-webapp.war) and deploy it to a Servlet container of your choice.

To create a Web Application that can be either packaged as WAR and deployed in a Servlet container or that can be pushed and deployed on Heroku the process is very similar to the one described in Section 1.4, “Creating a JavaEE Web Application”. To create the new web application skeleton project, execute the following Maven command in the directory where the new project should reside:

mvn archetype:generate -DarchetypeArtifactId=jersey-heroku-webapp \
                -DarchetypeGroupId=org.glassfish.jersey.archetypes -DinteractiveMode=false \
                -DgroupId=com.example -DartifactId=simple-heroku-webapp -Dpackage=com.example \
                -DarchetypeVersion=2.38-SNAPSHOT

Adjust the groupId, package and/or artifactId of your new web application project to your needs or, alternatively, you can change it by updating the new project pom.xml once it gets generated.

Once the project generation from a Jersey maven archetype is successfully finished, you should see the new simple-heroku-webapp project directory created in your current location. The directory contains a standard Maven project structure:

The project contains one JAX-RS resource class, MyResouce, and one resource method which returns simple text message. To make sure the resource is properly tested there is also a end-to-end test-case in MyResourceTest (the test is based on JerseyTest from our Chapter 28, Jersey Test Framework). Similarly to simple-service-webapp, the project contains the standard Java EE web application web.xml deployment descriptor under src/main/webapp/WEB-INF since the goal is to deploy the application in a Servlet container (the application will run in Jetty on Heroku).

To compile and package the application into a WAR, invoke the following maven command in your console:

mvn clean package

A successful build output will produce an output similar to the one below:

    Results :

    Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

    [INFO]
    [INFO] --- maven-war-plugin:2.2:war (default-war) @ simple-heroku-webapp ---
    [INFO] Packaging webapp
    [INFO] Assembling webapp [simple-heroku-webapp] in [.../simple-heroku-webapp/target/simple-heroku-webapp]
    [INFO] Processing war project
    [INFO] Copying webapp resources [.../simple-heroku-webapp/src/main/webapp]
    [INFO] Webapp assembled in [122 msecs]
    [INFO] Building war: .../simple-heroku-webapp/target/simple-heroku-webapp.war
    [INFO] WEB-INF/web.xml already added, skipping
    [INFO]
    [INFO] --- maven-dependency-plugin:2.8:copy-dependencies (copy-dependencies) @ simple-heroku-webapp ---
    [INFO] Copying jetty-util-9.4.28.v20200408.jar to .../simple-heroku-webapp/target/dependency/jetty-util-9.4.28.v20200408.jar
    [INFO] Copying jersey-hk2-2.33.jar to .../simple-heroku-webapp/target/dependency/jersey-hk2-2.33.jar
    [INFO] Copying javassist-3.25.0-GA.jar to .../simple-heroku-webapp/target/dependency/javassist-3.25.0-GA.jar
    [INFO] Copying jakarta.inject-2.6.1.jar to .../simple-heroku-webapp/target/dependency/jakarta.inject-2.6.1.jar
    [INFO] Copying hk2-locator-2.6.1.jar to .../simple-heroku-webapp/target/dependency/hk2-locator-2.6.1.jar
    [INFO] Copying hk2-utils-2.6.1.jar to .../simple-heroku-webapp/target/dependency/hk2-utils-2.6.1.jar
    [INFO] Copying hk2-api-2.6.1.jar to .../simple-heroku-webapp/target/dependency/hk2-api-2.6.1.jar
    [INFO] Copying jetty-webapp-9.4.28.v20200408.jar to .../simple-heroku-webapp/target/dependency/jetty-webapp-9.4.28.v20200408.jar
    [INFO] Copying jakarta.annotation-api-1.3.5.jar to .../simple-heroku-webapp/target/dependency/jakarta.annotation-api-1.3.5.jar
    [INFO] Copying jersey-server-2.33.jar to .../simple-heroku-webapp/target/dependency/jersey-server-2.33.jar
    [INFO] Copying jakarta.ws.rs-api-2.1.6.jar to .../simple-heroku-webapp/target/dependency/jakarta.ws.rs-api-2.1.6.jar
    [INFO] Copying osgi-resource-locator-1.0.3.jar to .../simple-heroku-webapp/target/dependency/osgi-resource-locator-1.0.3.jar
    [INFO] Copying aopalliance-repackaged-2.6.1.jar to .../simple-heroku-webapp/target/dependency/aopalliance-repackaged-2.6.1.jar
    [INFO] Copying jetty-servlet-9.4.28.v20200408.jar to .../simple-heroku-webapp/target/dependency/jetty-servlet-9.4.28.v20200408.jar
    [INFO] Copying jetty-xml-9.4.28.v20200408.jar to .../simple-heroku-webapp/target/dependency/jetty-xml-9.4.28.v20200408.jar
    [INFO] Copying jersey-container-servlet-2.33.jar to .../simple-heroku-webapp/target/dependency/jersey-container-servlet-2.33.jar
    [INFO] Copying jetty-io-9.4.28.v20200408.jar to .../simple-heroku-webapp/target/dependency/jetty-io-9.4.28.v20200408.jar
    [INFO] Copying jetty-security-9.4.28.v20200408.jar to .../simple-heroku-webapp/target/dependency/jetty-security-9.4.28.v20200408.jar
    [INFO] Copying jetty-server-9.4.28.v20200408.jar to .../simple-heroku-webapp/target/dependency/jetty-server-9.4.28.v20200408.jar
    [INFO] Copying javax.servlet-3.0.0.v201112011016.jar to .../simple-heroku-webapp/target/dependency/javax.servlet-3.0.0.v201112011016.jar
    [INFO] Copying jersey-common-2.33.jar to .../simple-heroku-webapp/target/dependency/jersey-common-2.33.jar
    [INFO] Copying jakarta.validation-api-2.0.2.jar to .../simple-heroku-webapp/target/dependency/jakarta.validation-api-2.0.2.jar
    [INFO] Copying jersey-container-servlet-core-2.33.jar to .../simple-heroku-webapp/target/dependency/jersey-container-servlet-core-2.33.jar
    [INFO] Copying jersey-client-2.33.jar to .../simple-heroku-webapp/target/dependency/jersey-client-2.33.jar
    [INFO] Copying jetty-http-9.4.28.v20200408.jar to .../simple-heroku-webapp/target/dependency/jetty-http-9.4.28.v20200408.jar
    [INFO] ------------------------------------------------------------------------
    [INFO] BUILD SUCCESS
    [INFO] ------------------------------------------------------------------------
    [INFO] Total time:  12.009 s
    [INFO] Finished at: 2021-01-29T08:48:04+01:00
    [INFO] ------------------------------------------------------------------------

Now that you know everything went as expected you are ready to:

    $ git init
    Initialized empty Git repository in /.../simple-heroku-webapp/.git/

    $ heroku create
    Creating simple-heroku-webapp... done, stack is cedar
    http://simple-heroku-webapp.herokuapp.com/ | git@heroku.com:simple-heroku-webapp.git
    Git remote heroku added

    $ git add src/ pom.xml Procfile system.properties

    $ git commit -a -m "initial commit"
    [master (root-commit) e2b58e3] initial commit
     7 files changed, 221 insertions(+)
     create mode 100644 Procfile
     create mode 100644 pom.xml
     create mode 100644 src/main/java/com/example/MyResource.java
     create mode 100644 src/main/java/com/example/heroku/Main.java
     create mode 100644 src/main/webapp/WEB-INF/web.xml
     create mode 100644 src/test/java/com/example/MyResourceTest.java
     create mode 100644 system.properties

    $ git push heroku master
    Counting objects: 21, done.
    Delta compression using up to 8 threads.
    Compressing objects: 100% (11/11), done.
    Writing objects: 100% (21/21), 3.73 KiB | 0 bytes/s, done.
    Total 21 (delta 0), reused 0 (delta 0)

    -----> Java app detected
    -----> Installing OpenJDK 1.8... done
    -----> Installing Maven 3.6.3... done
    -----> Installing settings.xml... done
    -----> executing /app/tmp/cache/.maven/bin/mvn -B -Duser.home=/tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd -Dmaven.repo.local=/app/tmp/cache/.m2/repository -s /app/tmp/cache/.m2/settings.xml -DskipTests=true clean install
    [INFO] Scanning for projects...
    [INFO]
    [INFO] ------------------ com.example:simple-heroku-webapp ------------------
    [INFO] Building simple-heroku-webapp 1.0-SNAPSHOT
    [INFO] --------------------------------[ war ]---------------------------------
    [INFO]
    [INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ simple-heroku-webapp ---
    [INFO] Deleting /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target
    [INFO]
    [INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ simple-heroku-webapp ---
    [INFO] Using 'UTF-8' encoding to copy filtered resources.
    [INFO] skip non existing resourceDirectory /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/src/main/resources
    [INFO]
    [INFO] --- maven-compiler-plugin:2.5.1:compile (default-compile) @ simple-heroku-webapp ---
    [INFO] Compiling 2 source files to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/classes
    [INFO]
    [INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ simple-heroku-webapp ---
    [INFO] Using 'UTF-8' encoding to copy filtered resources.
    [INFO] skip non existing resourceDirectory /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/src/test/resources
    [INFO]
    [INFO] --- maven-compiler-plugin:2.5.1:testCompile (default-testCompile) @ simple-heroku-webapp ---
    [INFO] Compiling 1 source file to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/test-classes
    [INFO]
    [INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ simple-heroku-webapp ---
    [INFO] Surefire report directory: /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/surefire-reports

    -------------------------------------------------------
    T E S T S
    -------------------------------------------------------
    Running com.example.MyResourceTest
    Jan 29, 2021 9:13:20 AM org.glassfish.jersey.test.grizzly.GrizzlyTestContainerFactory$GrizzlyTestContainer
    INFO: Creating GrizzlyTestContainer configured at the base URI http://localhost:9998/
    Jan 29, 2021 9:13:20 AM org.glassfish.jersey.server.wadl.WadlFeature configure
    WARNING: JAXBContext implementation could not be found. WADL feature is disabled.
    Jan 29, 2021 9:13:21 AM org.glassfish.grizzly.http.server.NetworkListener start
    INFO: Started listener bound to [localhost:9998]
    Jan 29, 2021 9:13:21 AM org.glassfish.grizzly.http.server.HttpServer start
    INFO: [HttpServer] Started.
    Jan 29, 2021 9:13:21 AM org.glassfish.grizzly.http.server.NetworkListener shutdownNow
    INFO: Stopped listener bound to [localhost:9998]
    Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 1.476 sec

    Results :

    Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

    [INFO]
    [INFO] --- maven-war-plugin:2.2:war (default-war) @ simple-heroku-webapp ---
    [INFO] Packaging webapp
    [INFO] Assembling webapp [simple-heroku-webapp] in [/tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/simple-heroku-webapp]
    [INFO] Processing war project
    [INFO] Copying webapp resources [/tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/src/main/webapp]
    [INFO] Webapp assembled in [115 msecs]
    [INFO] Building war: /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/simple-heroku-webapp.war
    [INFO] WEB-INF/web.xml already added, skipping
    [INFO]
    [INFO] --- maven-dependency-plugin:2.8:copy-dependencies (copy-dependencies) @ simple-heroku-webapp ---
    [INFO] Copying jetty-util-9.4.28.v20200408.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jetty-util-9.4.28.v20200408.jar
    [INFO] Copying jersey-hk2-2.33.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jersey-hk2-2.33.jar
    [INFO] Copying javassist-3.25.0-GA.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/javassist-3.25.0-GA.jar
    [INFO] Copying jakarta.inject-2.6.1.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jakarta.inject-2.6.1.jar
    [INFO] Copying hk2-locator-2.6.1.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/hk2-locator-2.6.1.jar
    [INFO] Copying hk2-utils-2.6.1.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/hk2-utils-2.6.1.jar
    [INFO] Copying hk2-api-2.6.1.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/hk2-api-2.6.1.jar
    [INFO] Copying jetty-webapp-9.4.28.v20200408.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jetty-webapp-9.4.28.v20200408.jar
    [INFO] Copying jakarta.annotation-api-1.3.5.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jakarta.annotation-api-1.3.5.jar
    [INFO] Copying jersey-server-2.33.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jersey-server-2.33.jar
    [INFO] Copying jakarta.ws.rs-api-2.1.6.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jakarta.ws.rs-api-2.1.6.jar
    [INFO] Copying osgi-resource-locator-1.0.3.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/osgi-resource-locator-1.0.3.jar
    [INFO] Copying aopalliance-repackaged-2.6.1.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/aopalliance-repackaged-2.6.1.jar
    [INFO] Copying jetty-servlet-9.4.28.v20200408.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jetty-servlet-9.4.28.v20200408.jar
    [INFO] Copying jetty-xml-9.4.28.v20200408.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jetty-xml-9.4.28.v20200408.jar
    [INFO] Copying jersey-container-servlet-2.33.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jersey-container-servlet-2.33.jar
    [INFO] Copying jetty-io-9.4.28.v20200408.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jetty-io-9.4.28.v20200408.jar
    [INFO] Copying jetty-security-9.4.28.v20200408.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jetty-security-9.4.28.v20200408.jar
    [INFO] Copying jetty-server-9.4.28.v20200408.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jetty-server-9.4.28.v20200408.jar
    [INFO] Copying javax.servlet-3.0.0.v201112011016.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/javax.servlet-3.0.0.v201112011016.jar
    [INFO] Copying jersey-common-2.33.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jersey-common-2.33.jar
    [INFO] Copying jakarta.validation-api-2.0.2.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jakarta.validation-api-2.0.2.jar
    [INFO] Copying jersey-container-servlet-core-2.33.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jersey-container-servlet-core-2.33.jar
    [INFO] Copying jersey-client-2.33.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jersey-client-2.33.jar
    [INFO] Copying jetty-http-9.4.28.v20200408.jar to /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/dependency/jetty-http-9.4.28.v20200408.jar
    [INFO]
    [INFO] --- maven-install-plugin:2.4:install (default-install) @ simple-heroku-webapp ---
    [INFO] Installing /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/target/simple-heroku-webapp.war to /app/tmp/cache/.m2/repository/com/example/simple-heroku-webapp/1.0-SNAPSHOT/simple-heroku-webapp-1.0-SNAPSHOT.war
    [INFO] Installing /tmp/build_992cc747-26d6-4800-bdb1-add47b9583cd/pom.xml to /app/tmp/cache/.m2/repository/com/example/simple-heroku-webapp/1.0-SNAPSHOT/simple-heroku-webapp-1.0-SNAPSHOT.pom
    [INFO] ------------------------------------------------------------------------
    [INFO] BUILD SUCCESS
    [INFO] ------------------------------------------------------------------------
    [INFO] Total time:  5.857 s
    [INFO] Finished at: 2021-01-29T09:13:23+01:00
    [INFO] ------------------------------------------------------------------------
    -----> Discovering process types
           Procfile declares types -> web

    -----> Compiled slug size: 75.9MB
    -----> Launching... done, v6
           http://simple-heroku-webapp.herokuapp.com deployed to Heroku

    To git@heroku.com:simple-heroku-webapp.git
     * [new branch]      master -> master

In the sections above, we have covered an approach how to get dirty with Jersey quickly. Please consult the other sections of the Jersey User Guide to learn more about Jersey and JAX-RS. Even though we try our best to cover as much as possible in the User Guide, there is always a chance that you would not be able to get a full answer to the problem you are solving. In that case, consider diving in our examples that provide additional tips and hints to the features you may want to use in your projects.

Jersey codebase contains a number of useful examples on how to use various JAX-RS and Jersey features. Feel free to browse through the code of individual Jersey Examples in the Jersey source repository. For off-line browsing, you can also download a bundle with all the examples from here.

2.x branch:

Jersey is built, assembled and installed using Apache Maven. Non-snapshot Jersey releases are deployed to the Central Maven Repository. Jersey is also being deployed to Sonatype Maven repositories, which contain also Jersey SNAPSHOT versions. In case you would want to test the latest development builds check out the Sonatype Snapshots Maven repository.

An application that uses Jersey and depends on Jersey modules is in turn required to also include in the application dependencies the set of 3rd party modules that Jersey modules depend on. Jersey is designed as a pluggable component architecture and different applications can therefore require different sets of Jersey modules. This also means that the set of external Jersey dependencies required to be included in the application dependencies may vary in each application based on the Jersey modules that are being used by the application.

Developers using Maven or a Maven-aware build system in their projects are likely to find it easier to include and manage dependencies of their applications compared to developers using ant or other build systems that are not compatible with Maven. This document will explain to both maven and non-maven developers how to depend on Jersey modules in their application. Ant developers are likely to find the Ant Tasks for Maven very useful.

The following chapters provide an overview of all Jersey modules and their dependencies with links to the respective binaries (follow a link on a module name to get complete set of downloadable dependencies).

Root resource classes are POJOs (Plain Old Java Objects) that are annotated with @Path have at least one method annotated with @Path or a resource method designator annotation such as @GET, @PUT, @POST, @DELETE. Resource methods are methods of a resource class annotated with a resource method designator. This section shows how to use Jersey to annotate Java objects to create RESTful web services.

The following code example is a very simple example of a root resource class using JAX-RS annotations. The example code shown here is from one of the samples that ships with Jersey, the zip file of which can be found in the maven repository here.

package org.glassfish.jersey.examples.helloworld;

import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.Produces;

@Path("helloworld")
public class HelloWorldResource {
    public static final String CLICHED_MESSAGE = "Hello World!";

@GET
@Produces("text/plain")
    public String getHello() {
        return CLICHED_MESSAGE;
    }
}

Let's look at some of the JAX-RS annotations used in this example.

@Path("/users/{username}")

@Path("/users/{username}")
public class UserResource {

    @GET
    @Produces("text/xml")
    public String getUser(@PathParam("username") String userName) {
        ...
    }
}

@Path("users/{username: [a-zA-Z][a-zA-Z_0-9]*}")

@PUT
public Response putContainer() {
    System.out.println("PUT CONTAINER " + container);

    URI uri = uriInfo.getAbsolutePath();
    Container c = new Container(container, uri.toString());

    Response r;
    if (!MemoryStore.MS.hasContainer(c)) {
        r = Response.created(uri).build();
    } else {
        r = Response.noContent().build();
    }

    MemoryStore.MS.createContainer(c);
    return r;
}

@Path("/myResource")
@Produces("text/plain")
public class SomeResource {
    @GET
    public String doGetAsPlainText() {
        ...
    }

    @GET
    @Produces("text/html")
    public String doGetAsHtml() {
        ...
    }
}

@GET
@Produces({"application/xml", "application/json"})
public String doGetAsXmlOrJson() {
    ...
}

@GET
@Produces({"application/xml; qs=0.9", "application/json"})
public String doGetAsXmlOrJson() {
    ...
}

@POST
@Consumes("text/plain")
public void postClichedMessage(String message) {
    // Store the message
}

Parameters of a resource method may be annotated with parameter-based annotations to extract information from a request. One of the previous examples presented the use of @PathParam to extract a path parameter from the path component of the request URL that matched the path declared in @Path.

@QueryParam is used to extract query parameters from the Query component of the request URL. The following example is an extract from the sparklines sample:

@Path("smooth")
@GET
public Response smooth(
    @DefaultValue("2") @QueryParam("step") int step,
    @DefaultValue("true") @QueryParam("min-m") boolean hasMin,
    @DefaultValue("true") @QueryParam("max-m") boolean hasMax,
    @DefaultValue("true") @QueryParam("last-m") boolean hasLast,
    @DefaultValue("blue") @QueryParam("min-color") ColorParam minColor,
    @DefaultValue("green") @QueryParam("max-color") ColorParam maxColor,
    @DefaultValue("red") @QueryParam("last-color") ColorParam lastColor) {
    ...
}

If a query parameter "step" exists in the query component of the request URI then the "step" value will be extracted and parsed as a 32 bit signed integer and assigned to the step method parameter. If "step" does not exist then a default value of 2, as declared in the @DefaultValue annotation, will be assigned to the step method parameter. If the "step" value cannot be parsed as a 32 bit signed integer then a HTTP 404 (Not Found) response is returned. User defined Java types such as ColorParam may be used, which as implemented as follows:

public class ColorParam extends Color {

    public ColorParam(String s) {
        super(getRGB(s));
    }

    private static int getRGB(String s) {
        if (s.charAt(0) == '#') {
            try {
                Color c = Color.decode("0x" + s.substring(1));
                return c.getRGB();
            } catch (NumberFormatException e) {
                throw new WebApplicationException(400);
            }
        } else {
            try {
                Field f = Color.class.getField(s);
                return ((Color)f.get(null)).getRGB();
            } catch (Exception e) {
                throw new WebApplicationException(400);
            }
        }
    }
}

In general the Java type of the method parameter may:

Sometimes parameters may contain more than one value for the same name. If this is the case then types in 5) may be used to obtain all values.

If the @DefaultValue is not used in conjunction with @QueryParam and the query parameter is not present in the request then value will be an empty collection forList, Set or SortedSet, null for other object types, and the Java-defined default for primitive types.

The @PathParam and the other parameter-based annotations, @MatrixParam, @HeaderParam, @CookieParam, @FormParam obey the same rules as @QueryParam. @MatrixParam extracts information from URL path segments. @HeaderParam extracts information from the HTTP headers. @CookieParam extracts information from the cookies declared in cookie related HTTP headers.

@FormParam is slightly special because it extracts information from a request representation that is of the MIME media type "application/x-www-form-urlencoded" and conforms to the encoding specified by HTML forms, as described here. This parameter is very useful for extracting information that is POSTed by HTML forms, for example the following extracts the form parameter named "name" from the POSTed form data:

@POST
@Consumes("application/x-www-form-urlencoded")
public void post(@FormParam("name") String name) {
    // Store the message
}

If it is necessary to obtain a general map of parameter name to values then, for query and path parameters it is possible to do the following:

@GET
public String get(@Context UriInfo ui) {
    MultivaluedMap<String, String> queryParams = ui.getQueryParameters();
    MultivaluedMap<String, String> pathParams = ui.getPathParameters();
}

For header and cookie parameters the following:

@GET
public String get(@Context HttpHeaders hh) {
    MultivaluedMap<String, String> headerParams = hh.getRequestHeaders();
    Map<String, Cookie> pathParams = hh.getCookies();
}

In general @Context can be used to obtain contextual Java types related to the request or response.

Because form parameters (unlike others) are part of the message entity, it is possible to do the following:

@POST
@Consumes("application/x-www-form-urlencoded")
public void post(MultivaluedMap<String, String> formParams) {
    // Store the message
}

I.e. you don't need to use the @Context annotation.

Another kind of injection is the @BeanParam which allows to inject the parameters described above into a single bean. A bean annotated with @BeanParam containing any fields and appropriate *param annotation(like @PathParam) will be initialized with corresponding request values in expected way as if these fields were in the resource class. Then instead of injecting request values like path param into a constructor parameters or class fields the @BeanParam can be used to inject such a bean into a resource or resource method. The @BeanParam is used this way to aggregate more request parameters into a single bean.

public class MyBeanParam {
    @PathParam("p")
    private String pathParam;

    @MatrixParam("m")
    @Encoded
    @DefaultValue("default")
    private String matrixParam;

    @HeaderParam("header")
    private String headerParam;

    private String queryParam;

    public MyBeanParam(@QueryParam("q") String queryParam) {
        this.queryParam = queryParam;
    }

    public String getPathParam() {
        return pathParam;
    }
    ...
}

@POST
public void post(@BeanParam MyBeanParam beanParam, String entity) {
    final String pathParam = beanParam.getPathParam(); // contains injected path parameter "p"
    ...
}

The example shows aggregation of injections @PathParam, @QueryParam @MatrixParam and @HeaderParam into one single bean. The rules for injections inside the bean are the same as described above for these injections. The @DefaultValue is used to define the default value for matrix parameter matrixParam. Also the @Encoded annotation has the same behaviour as if it were used for injection in the resource method directly. Injecting the bean parameter into @Singleton resource class fields is not allowed (injections into method parameter must be used instead).

@BeanParam can contain all parameters injections (@PathParam, @QueryParam, @MatrixParam, @HeaderParam, @CookieParam, @FormParam). More beans can be injected into one resource or method parameters even if they inject the same request values. For example the following is possible:

@POST
public void post(@BeanParam MyBeanParam beanParam, @BeanParam AnotherBean anotherBean, @PathParam("p") pathParam,
String entity) {
    // beanParam.getPathParam() == pathParam
    ...
}

@Path may be used on classes and such classes are referred to as root resource classes. @Path may also be used on methods of root resource classes. This enables common functionality for a number of resources to be grouped together and potentially reused.

The first way @Path may be used is on resource methods and such methods are referred to as sub-resource methods. The following example shows the method signatures for a root resource class from the jmaki-backend sample:

@Singleton
@Path("/printers")
public class PrintersResource {

    @GET
    @Produces({"application/json", "application/xml"})
    public WebResourceList getMyResources() { ... }

    @GET @Path("/list")
    @Produces({"application/json", "application/xml"})
    public WebResourceList getListOfPrinters() { ... }

    @GET @Path("/jMakiTable")
    @Produces("application/json")
    public PrinterTableModel getTable() { ... }

    @GET @Path("/jMakiTree")
    @Produces("application/json")
    public TreeModel getTree() { ... }

    @GET @Path("/ids/{printerid}")
    @Produces({"application/json", "application/xml"})
    public Printer getPrinter(@PathParam("printerid") String printerId) { ... }

    @PUT @Path("/ids/{printerid}")
    @Consumes({"application/json", "application/xml"})
    public void putPrinter(@PathParam("printerid") String printerId, Printer printer) { ... }

    @DELETE @Path("/ids/{printerid}")
    public void deletePrinter(@PathParam("printerid") String printerId) { ... }
}

If the path of the request URL is "printers" then the resource methods not annotated with @Path will be selected. If the request path of the request URL is "printers/list" then first the root resource class will be matched and then the sub-resource methods that match "list" will be selected, which in this case is the sub-resource method getListOfPrinters. So, in this example hierarchical matching on the path of the request URL is performed.

The second way @Path may be used is on methods not annotated with resource method designators such as @GET or @POST. Such methods are referred to as sub-resource locators. The following example shows the method signatures for a root resource class and a resource class from the optimistic-concurrency sample:

@Path("/item")
public class ItemResource {
    @Context UriInfo uriInfo;

    @Path("content")
    public ItemContentResource getItemContentResource() {
        return new ItemContentResource();
    }

    @GET
    @Produces("application/xml")
        public Item get() { ... }
    }
}

public class ItemContentResource {

    @GET
    public Response get() { ... }

    @PUT
    @Path("{version}")
    public void put(@PathParam("version") int version,
                    @Context HttpHeaders headers,
                    byte[] in) {
        ...
    }
}

The root resource class ItemResource contains the sub-resource locator method getItemContentResource that returns a new resource class. If the path of the request URL is "item/content" then first of all the root resource will be matched, then the sub-resource locator will be matched and invoked, which returns an instance of the ItemContentResource resource class. Sub-resource locators enable reuse of resource classes. A method can be annotated with the @Path annotation with empty path (@Path("/") or @Path("")) which means that the sub resource locator is matched for the path of the enclosing resource (without sub-resource path).

@Path("/item")
public class ItemResource {

    @Path("/")
    public ItemContentResource getItemContentResource() {
        return new ItemContentResource();
    }
}

In the example above the sub-resource locator method getItemContentResource is matched for example for request path "/item/locator" or even for only "/item".

In addition the processing of resource classes returned by sub-resource locators is performed at runtime thus it is possible to support polymorphism. A sub-resource locator may return different sub-types depending on the request (for example a sub-resource locator could return different sub-types dependent on the role of the principle that is authenticated). So for example the following sub resource locator is valid:

@Path("/item")
public class ItemResource {

    @Path("/")
    public Object getItemContentResource() {
        return new AnyResource();
    }
}

Note that the runtime will not manage the life-cycle or perform any field injection onto instances returned from sub-resource locator methods. This is because the runtime does not know what the life-cycle of the instance is. If it is required that the runtime manages the sub-resources as standard resources the Class should be returned as shown in the following example:

import javax.inject.Singleton;

@Path("/item")
public class ItemResource {
    @Path("content")
    public Class<ItemContentSingletonResource> getItemContentResource() {
        return ItemContentSingletonResource.class;
    }
}

@Singleton
public class ItemContentSingletonResource {
    // this class is managed in the singleton life cycle
}

JAX-RS resources are managed in per-request scope by default which means that new resource is created for each request. In this example the javax.inject.Singleton annotation says that the resource will be managed as singleton and not in request scope. The sub-resource locator method returns a class which means that the runtime will managed the resource instance and its life-cycle. If the method would return instance instead, the Singleton annotation would have no effect and the returned instance would be used.

The sub resource locator can also return a programmatic resource model. See resource builder section for information of how the programmatic resource model is constructed. The following example shows very simple resource returned from the sub-resource locator method.

import org.glassfish.jersey.server.model.Resource;

@Path("/item")
public class ItemResource {

    @Path("content")
    public Resource getItemContentResource() {
        return Resource.from(ItemContentSingletonResource.class);
    }
}

The code above has exactly the same effect as previous example. Resource is a resource simple resource constructed from ItemContentSingletonResource. More complex programmatic resource can be returned as long they are valid resources.

By default the life-cycle of root resource classes is per-request which, namely that a new instance of a root resource class is created every time the request URI path matches the root resource. This makes for a very natural programming model where constructors and fields can be utilized (as in the previous section showing the constructor of the SparklinesResource class) without concern for multiple concurrent requests to the same resource.

In general this is unlikely to be a cause of performance issues. Class construction and garbage collection of JVMs has vastly improved over the years and many objects will be created and discarded to serve and process the HTTP request and return the HTTP response.

Instances of singleton root resource classes can be declared by an instance of Application.

Jersey supports two further life-cycles using Jersey specific annotations.

Previous sections have presented examples of annotated types, mostly annotated method parameters but also annotated fields of a class, for the injection of values onto those types.

This section presents the rules of injection of values on annotated types. Injection can be performed on fields, constructor parameters, resource/sub-resource/sub-resource locator method parameters and bean setter methods. The following presents an example of all such injection cases:

@Path("{id:\\d+}")
public class InjectedResource {
    // Injection onto field
    @DefaultValue("q") @QueryParam("p")
    private String p;

    // Injection onto constructor parameter
    public InjectedResource(@PathParam("id") int id) { ... }

    // Injection onto resource method parameter
    @GET
    public String get(@Context UriInfo ui) { ... }

    // Injection onto sub-resource resource method parameter
    @Path("sub-id")
    @GET
    public String get(@PathParam("sub-id") String id) { ... }

    // Injection onto sub-resource locator method parameter
    @Path("sub-id")
    public SubResource getSubResource(@PathParam("sub-id") String id) { ... }

    // Injection using bean setter method
    @HeaderParam("X-header")
    public void setHeader(String header) { ... }
}

There are some restrictions when injecting on to resource classes with a life-cycle of singleton scope. In such cases the class fields or constructor parameters cannot be injected with request specific parameters. So, for example the following is not allowed.

@Path("resource")
@Singleton
public static class MySingletonResource {

    @QueryParam("query")
    String param; // WRONG: initialization of application will fail as you cannot
                  // inject request specific parameters into a singleton resource.

    @GET
    public String get() {
        return "query param: " + param;
    }
}

The example above will cause validation failure during application initialization as singleton resources cannot inject request specific parameters. The same example would fail if the query parameter would be injected into constructor parameter of such a singleton. In other words, if you wish one resource instance to server more requests (in the same time) it cannot be bound to a specific request parameter.

The exception exists for specific request objects which can injected even into constructor or class fields. For these objects the runtime will inject proxies which are able to simultaneously server more request. These request objects are HttpHeaders, Request, UriInfo, SecurityContext. These proxies can be injected using the @Context annotation. The following example shows injection of proxies into the singleton resource class.

@Path("resource")
@Singleton
public static class MySingletonResource {
    @Context
    Request request; // this is ok: the proxy of Request will be injected into this singleton

    public MySingletonResource(@Context SecurityContext securityContext) {
        // this is ok too: the proxy of SecurityContext will be injected
    }

    @GET
    public String get() {
        return "query param: " + param;
    }
}

To summarize the injection can be done into the following constructs:

The following example shows all possible java constructs into which the values can be injected.

@Path("resource")
public static class SummaryOfInjectionsResource {
    @QueryParam("query")
    String param; // injection into a class field


    @GET
    public String get(@QueryParam("query") String methodQueryParam) {
        // injection into a resource method parameter
        return "query param: " + param;
    }

    @Path("sub-resource-locator")
    public Class<SubResource> subResourceLocator(@QueryParam("query") String subResourceQueryParam) {
        // injection into a sub resource locator parameter
        return SubResource.class;
    }

    public SummaryOfInjectionsResource(@QueryParam("query") String constructorQueryParam) {
        // injection into a constructor parameter
    }


    @Context
    public void setRequest(Request request) {
        // injection into a setter method
        System.out.println(request != null);
    }
}

public static class SubResource {
    @GET
    public String get() {
        return "sub resource";
    }
}

The @FormParam annotation is special and may only be utilized on resource and sub-resource methods. This is because it extracts information from a request entity.

Previous sections have introduced the use of @Context. Chapter "Context" in the JAX-RS specification presents all the standard JAX-RS Java types that may be used with @Context.

When deploying a JAX-RS application using servlet then ServletConfig, ServletContext, HttpServletRequest and HttpServletResponse are available using @Context.

Resources can be constructed from classes or instances but also can be constructed from a programmatic resource model. Every resource created from resource classes can also be constructed using the programmatic resource builder api. See resource builder section for more information.

This chapter is an overview of various server-side environments currently capable of running JAX-RS applications on top of Jersey server runtime. Jersey supports wide range of server environments from lightweight http containers up to full-fledged Java EE servers. Jersey applications can also run in an OSGi runtime. The way how the application is published depends on whether the application shall run in a Java SE environment or within a container.

JAX-RS provides a deployment agnostic abstract class Application for declaring root resource and provider classes, and root resource and provider singleton instances. A Web service may extend this class to declare root resource and provider classes. For example,

public class MyApplication extends Application {
    @Override
    public Set<Class<?>> getClasses() {
        Set<Class<?>> s = new HashSet<Class<?>>();
        s.add(HelloWorldResource.class);
        return s;
    }
}

Alternatively it is possible to reuse ResourceConfig - Jersey's own implementations of Application class. This class can either be directly instantiated and then configured or it can be extended and the configuration code placed into the constructor of the extending class. The approach typically depends on the chosen deployment runtime.

Compared to Application, the ResourceConfig provides advanced capabilities to simplify registration of JAX-RS components, such as scanning for root resource and provider classes in a provided classpath or a set of package names etc. All JAX-RS component classes that are either manually registered or found during scanning are automatically added to the set of classes that are returned by getClasses. For example, the following application class that extends from ResourceConfig scans during deployment for JAX-RS components in packages org.foo.rest and org.bar.rest:

public class MyApplication extends ResourceConfig {
    public MyApplication() {
        packages("org.foo.rest;org.bar.rest");
    }
}

By default Jersey 2.x does not implicitly register any extension features from the modules available on the classpath, unless explicitly stated otherwise in the documentation of each particular extension. Users are expected to explicitly register the extension Features using their Application subclass. For a few Jersey provided modules however there is no need to explicitly register their extension Features as these are discovered and registered in the Configuration (on client/server) automatically by Jersey runtime whenever the modules implementing these features are present on the classpath of the deployed JAX-RS application. The modules that are automatically discovered include:

Besides these modules there are also few features/providers present in jersey-server module that are discovered by this mechanism and their availability is affected by Jersey auto-discovery support configuration (see Section 4.3.1, “Configuring Feature Auto-discovery Mechanism”), namely:

Almost all Jersey auto-discovery implementations have AutoDiscoverable.DEFAULT_PRIORITY @Priority set.

Jersey uses a common Java Service Provider mechanism to obtain all service implementations. It means that Jersey scans the whole class path to find appropriate META-INF/services/ files. The class path scanning may be time consuming. The more jar or war files on the classpath the longer the scanning time. In use cases where you need to save every millisecond of application bootstrap time, you may typically want to disable the services provider lookup in Jersey.

Since it is possible to configure all SPI implementation classes or instances manually in your Application subclass, disabling services lookup in Jersey does not affect any functionality of Jersey core modules and extensions and can save dozens of ms during application initialization in exchange for a more verbose application configuration code.

The services lookup in Jersey (enabled by default) can be disabled via a dedicated CommonProperties.METAINF_SERVICES_LOOKUP_DISABLE property. There is a client/server counter-part that only disables the feature on the client or server respectively: ClientProperties.METAINF_SERVICES_LOOKUP_DISABLE/ServerProperties.METAINF_SERVICES_LOOKUP_DISABLE. As in all other cases, the client/server specific properties overrides the value of the related common property, when set.

For example, following code snippet disables service provider lookup and manually registers implementations of different JAX-RS and Jersey provider types (ContainerRequestFilter, Feature, ComponentProvider and ContainerProvider):

ResourceConfig resourceConfig = new ResourceConfig(MyResource.class);
resourceConfig.register(org.glassfish.jersey.server.filter.UriConnegFilter.class);
resourceConfig.register(org.glassfish.jersey.server.validation.ValidationFeature.class);
resourceConfig.register(org.glassfish.jersey.server.spring.SpringComponentProvider.class);
resourceConfig.register(org.glassfish.jersey.grizzly2.httpserver.GrizzlyHttpContainerProvider.class);
resourceConfig.property(ServerProperties.METAINF_SERVICES_LOOKUP_DISABLE, true);

Similarly, in scenarios where the deployment model requires extending the Application subclass (e.g. in all Servlet container deployments), the following code could be used to achieve the same application configuration:

public class MyApplication extends ResourceConfig {
    public MyApplication() {
        register(org.glassfish.jersey.server.filter.UriConnegFilter.class);
        register(org.glassfish.jersey.server.validation.ValidationFeature.class);
        register(org.glassfish.jersey.server.spring.SpringComponentProvider.class);
        register(org.glassfish.jersey.grizzly2.httpserver.GrizzlyHttpContainerProvider.class);
        property(ServerProperties.METAINF_SERVICES_LOOKUP_DISABLE, true);
    }
}

JAX-RS specification also defines the ability to programmatically create a JAX-RS application endpoint (i.e. container) for any instance of a Application subclass. For example, Jersey supports creation of Grizzly HttpHandler instance as follows:

HttpHandler endpoint = RuntimeDelegate.getInstance()
        .createEndpoint(new MyApplication(), HttpHandler.class);

Once the Grizzly HttpHandler endpoint is created, it can be used for in-process deployment to a specific base URL.

In a Servlet container, JAX-RS defines multiple deployment options depending on the Servlet API version supported by the Servlet container. Following sections describe these options in detail.

<web-app>
    <servlet>
        <servlet-name>MyApplication</servlet-name>
        <servlet-class>org.glassfish.jersey.servlet.ServletContainer</servlet-class>
        <init-param>
            ...
        </init-param>
    </servlet>
    ...
    <servlet-mapping>
        <servlet-name>MyApplication</servlet-name>
        <url-pattern>/myApp/*</url-pattern>
    </servlet-mapping>
    ...
</web-app>

<web-app>
    <filter>
        <filter-name>MyApplication</filter-name>
        <filter-class>org.glassfish.jersey.servlet.ServletContainer</filter-class>
        <init-param>
            ...
        </init-param>
    </filter>
    ...
    <filter-mapping>
        <filter-name>MyApplication</filter-name>
        <url-pattern>/myApp/*</url-pattern>
    </filter-mapping>
    ...
</web-app>

<init-param>
    <param-name>javax.ws.rs.Application</param-name>
    <param-value>org.foo.MyApplication</param-value>
</init-param>

<init-param>
    <param-name>jersey.config.server.provider.packages</param-name>
    <param-value>
        org.foo.myresources,org.bar.otherresources
    </param-value>
</init-param>
<init-param>
    <param-name>jersey.config.server.provider.scanning.recursive</param-name>
    <param-value>false</param-value>
</init-param>

<init-param>
    <param-name>jersey.config.server.provider.classnames</param-name>
    <param-value>
        org.foo.myresources.MyDogResource,
        org.bar.otherresources.MyCatResource
    </param-value>
</init-param>

@ApplicationPath("resources")
public class MyApplication extends ResourceConfig {
    public MyApplication() {
        packages("org.foo.rest;org.bar.rest");
    }
}

<plugins>
    ...
    <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-war-plugin</artifactId>
        <version>2.3</version>
        <configuration>
            <failOnMissingWebXml>false</failOnMissingWebXml>
        </configuration>
    </plugin>
    ...
</plugins>

<web-app>
    <servlet>
        <servlet-name>org.foo.rest.MyApplication</servlet-name>
    </servlet>
    ...
    <servlet-mapping>
        <servlet-name>org.foo.rest.MyApplication</servlet-name>
        <url-pattern>/resources</url-pattern>
    </servlet-mapping>
    ...
</web-app>

<web-app version="3.0"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

    <!-- Servlet declaration can be omitted in which case
         it would be automatically added by Jersey -->
    <servlet>
        <servlet-name>javax.ws.rs.core.Application</servlet-name>
    </servlet>

    <servlet-mapping>
        <servlet-name>javax.ws.rs.core.Application</servlet-name>
        <url-pattern>/myresources/*</url-pattern>
    </servlet-mapping>
</web-app>

<web-app version="3.0"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

    <!-- Servlet declaration can be omitted in which case
         it would be automatically added by Jersey -->
    <servlet>
        <servlet-name>org.example.MyApplication</servlet-name>
    </servlet>

    <!-- Servlet mapping can be omitted in case the Application subclass
         is annotated with @ApplicationPath annotation; in such case
         the mapping would be automatically added by Jersey -->
    <servlet-mapping>
        <servlet-name>org.example.MyApplication</servlet-name>
        <url-pattern>/myresources/*</url-pattern>
    </servlet-mapping>
</web-app>

<dependency>
    <groupId>org.glassfish.jersey.containers</groupId>
    <artifactId>jersey-container-servlet-core</artifactId>
</dependency>

<dependency>
    <groupId>org.glassfish.jersey.containers</groupId>
    <artifactId>jersey-container-servlet</artifactId>
</dependency>

This section describes, how you can publish Jersey JAX-RS resources as various Java EE platform elements. JAX-RS and Jersey give you wide choice of possibilities and it is up to your taste (and design of your application), what Java EE technology you decide to use for the management of your resources.

@ManagedBean
@Path("/managedbean")
public class ManagedBeanResource {

    public static class MyInterceptor {
        @AroundInvoke
        public String around(InvocationContext ctx) throws Exception {
            System.out.println("around() called");
            return (String) ctx.proceed();
        }
    }

    @GET
    @Produces("text/plain")
    @Interceptors(MyInterceptor.class)
    public String getIt() {
        return "Hi managed bean!";
    }
}

@Path("/cdibean")
public class CdiBeanResource {
    @Inject MyOtherCdiBean bean;  // CDI injected bean

    @GET
    @Produces("text/plain")
    public String getIt() {
        return bean.getIt();
    }
}

@Local
public interface LocalEjb {
    @GET
    @Produces("text/plain")
   public String getIt();
}

@Stateless
@Path("/stateless")
public class StatelessEjbResource implements LocalEjb {
    @Override
    public String getIt() {
        return "Hi Stateless!";
    }
}

OSGi support has been added to the Jersey version 1.2. Since then, you should be able to utilize standard OSGi means to run Jersey based web applications in OSGi runtime as described in the OSGi Service Platform Enterprise Specification. Jersey is currently compatible with OSGi 4.2.0, the specification could be downloaded from the OSGi 4.2.0 Download Site.

The two supported ways of running an OSGi web application are:

WAB is in fact just an OSGified WAR archive. HTTP Service feature allows you to publish Java EE Servlets in the OSGi runtime.

Two examples were added to the Jersey distribution to depict the above mentioned features and show how to use them with Jersey:

Both examples are multi-module maven projects and both consist of an application OSGi bundle module and a test module. The tests are based on the PAX Exam framework. Both OSGi examples also include a readme file containing instructions how to manually run the example applications using Apache Felix framework.

The rest of the chapter describes how to run the above mentioned examples on GlassFish 4 application server.

~/glassfish/bin$ ./asadmin
Use "exit" to exit and "help" for online help.
asadmin>

asadmin>  list-jvm-options
...
-Dglassfish.osgi.start.level.final=2
...

asadmin>  create-jvm-options --target server -Dglassfish.osgi.start.level.final=3

# Final start level of OSGi framework. This is used by GlassFish launcher code
# to set the start level of the OSGi framework once server is up and running so that
# optional services can start. The initial start level of framework is controlled using
# the standard framework property called org.osgi.framework.startlevel.beginning
glassfish.osgi.start.level.final=3

asadmin> osgi lb
... list of bundles ...

asadmin> osgi-shell
Use "exit" to exit and "help" for online help.
gogo$

gogo$ lb
... list of bundles ...

Web-ContextPath: helloworld
Webapp-Context: helloworld
Bundle-ClassPath: WEB-INF/classese

examples$ cd osgi-http-service/bundle
bundle$ mvn clean package

gogo$ install file:///path/to/file/bundle.jar
Bundle ID: 303

gogo$ install http://central.maven.org/maven2/org/glassfish/jersey/examples/osgi-http-service/bundle/<version>/bundle-<version>.jar
Bundle ID: 303

gogo$ lb
...
303 | Installed  |    1| jersey-examples-osgi-http-service-bundle (2.5.0.SNAPSHOT)
gogo$ start 303

org.osgi.framework.BundleException: Unresolved constraint in bundle
org.glassfish.jersey.examples.osgi-http-service.bundle [303]: Unable to resolve 308.0: missing requirement
[303.0] osgi.wiring.package; (&(osgi.wiring.package=org.glassfish.jersey.servlet)
(version>=2.5.0)(!(version>=3.0.0)))

gogo$

gogo$ start 303

The uniform interface constraint bounds the architecture of RESTful Web services so that a client, such as a browser, can utilize the same interface to communicate with any service. This is a very powerful concept in software engineering that makes Web-based search engines and service mash-ups possible. It induces properties such as:

Further constraints are required:

The above process repeated over and again should be familiar to anyone who has used a browser to fill in HTML forms and follow links. That same process is applicable to non-browser based clients.

Many existing Java-based client APIs, such as the Apache HTTP client API or HttpUrlConnection supplied with the JDK place too much focus on the Client-Server constraint for the exchanges of request and responses rather than a resource, identified by a URI, and the use of a fixed set of HTTP methods.

A resource in the JAX-RS client API is an instance of the Java class WebTarget. and encapsulates an URI. The fixed set of HTTP methods can be invoked based on the WebTarget. The representations are Java types, instances of which, may contain links that new instances of WebTarget may be created from.

Since a JAX-RS component is represented as an annotated Java type, it makes it easy to configure, pass around and inject in ways that are not so intuitive or possible with other client-side APIs. The Jersey Client API reuses many aspects of the JAX-RS and the Jersey implementation such as:

Some APIs, like the Apache HTTP Client or HttpURLConnection can be rather hard to use and/or require too much code to do something relatively simple, especially when the client needs to understand different payload representations. This is why the Jersey implementation of JAX-RS Client API provides support for wrapping HttpUrlConnection and the Apache HTTP client. Thus it is possible to get the benefits of the established JAX-RS implementations and features while getting the ease of use benefit of the simple design of the JAX-RS client API. For example, with a low-level HTTP client library, sending a POST request with a bunch of typed HTML form parameters and receiving a response de-serialized into a JAXB bean is not straightforward at all. With the new JAX-RS Client API supported by Jersey this task is very easy:

Client client = ClientBuilder.newClient();
WebTarget target = client.target("http://localhost:9998").path("resource");

Form form = new Form();
form.param("x", "foo");
form.param("y", "bar");

MyJAXBBean bean =
target.request(MediaType.APPLICATION_JSON_TYPE)
    .post(Entity.entity(form,MediaType.APPLICATION_FORM_URLENCODED_TYPE),
        MyJAXBBean.class);

In the Example 5.1, “POST request with form parameters” a new WebTarget instance is created using a new Client instance first, next a Form instance is created with two form parameters. Once ready, the Form instance is POSTed to the target resource. First, the acceptable media type is specified in the request(...) method. Then in the post(...) method, a call to a static method on JAX-RS Entity is made to construct the request entity instance and attach the proper content media type to the form entity that is being sent. The second parameter in the post(...) method specifies the Java type of the response entity that should be returned from the method in case of a successful response. In this case an instance of JAXB bean is requested to be returned on success. The Jersey client API takes care of selecting the proper MessageBodyWriter<T> for the serialization of the Form instance, invoking the POST request and producing and de-serialization of the response message payload into an instance of a JAXB bean using a proper MessageBodyReader<T>.

If the code above had to be written using HttpUrlConnection, the developer would have to write custom code to serialize the form data that are sent within the POST request and de-serialize the response input stream into a JAXB bean. Additionally, more code would have to be written to make it easy to reuse the logic when communicating with the same resource “http://localhost:8080/resource” that is represented by the JAX-RS WebTarget instance in our example.

All the Java types and representations supported by default on the Jersey server side for requests and responses are also supported on the client side. For example, to process a response entity (or representation) as a stream of bytes use InputStream as follows:

InputStream in = response.readEntity(InputStream.class);

... // Read from the stream

in.close();
            

Note that it is important to close the stream after processing so that resources are freed up.

To POST a file use a File instance as follows:

File f = ...

...

webTarget.request().post(Entity.entity(f, MediaType.TEXT_PLAIN_TYPE));
            

By default, the transport layer in Jersey is provided by HttpUrlConnection. This transport is implemented in Jersey via HttpUrlConnectorProvider that implements Jersey-specific Connector SPI. You can implement and/or register your own Connector instance to the Jersey Client implementation, that will replace the default HttpUrlConnection-based transport layer. Jersey provides several alternative client transport connector implementations that are ready-to-use.

                            Client client = ClientBuilder.newClient();
                            System.setProperty("sun.net.http.allowRestrictedHeaders", "true");

                            Response response = client.target(yourUri).path(yourPath).request().
                            header("Origin", "http://example.com").
                            header("Access-Control-Request-Method", "POST").
                            get();
                        

As indicated earlier, Connector and ConnectorProvider contracts are Jersey-specific extension APIs that would only work with Jersey and as such are not part of JAX-RS. Following example shows how to setup the custom Grizzly Asynchronous HTTP Client based ConnectorProvider in a Jersey client instance:

ClientConfig clientConfig = new ClientConfig();
clientConfig.connectorProvider(new GrizzlyConnectorProvider());
Client client = ClientBuilder.newClient(clientConfig);

Client accepts as a constructor argument a Configurable instance. Jersey implementation of the Configurable provider for the client is ClientConfig. By using the Jersey ClientConfig you can configure the custom ConnectorProvider into the ClientConfig. The GrizzlyConnectorProvider is used as a custom connector provider in the example above. Please note that the connector provider cannot be registered as a provider using Configurable.register(...). Also, please note that in this API has changed in Jersey 2.5, where the ConnectorProvider SPI has been introduced in order to decouple client initialization from the connector instantiation. Starting with Jersey 2.5 it is therefore not possible to directly register Connector instances in the Jersey ClientConfig. The new ConnectorProvider SPI must be used instead to configure a custom client-side transport connector.

                        org.apache.http.client.CredentialsProvider credentialsProvider = new org.apache.http.impl.client.BasicCredentialsProvider();
                        credentialsProvider.setCredentials(
                            org.apache.http.auth.AuthScope.ANY,
                            new org.apache.http.auth.UsernamePasswordCredentials("name", "password")
                        );
                        ApacheHttpClientBuilderConfigurator apacheHttpClientBuilderConfigurator = (httpClientBuilder) -> {
                            return httpClientBuilder.setDefaultCredentialsProvider(credentialsProvider);
                        };

                        ClientConfig cc = new ClientConfig();
                        cc.register(apacheHttpClientBuilderConfigurator);
                        cc.connectorProvider(new ApacheConnectorProvider());
                        Client client = ClientBuilder.newClient(cc);
                        ...
                    

                        org.apache.hc.client5.http.auth.CredentialsStore credentialsProvider = new org.apache.hc.client5.http.impl.auth.BasicCredentialsProvider();
                        credentialsProvider.setCredentials(
                            new org.apache.hc.client5.http.auth.AuthScope("localhost", getPort()),
                            new org.apache.hc.client5.http.auth.UsernamePasswordCredentials("name", "password".toCharArray())
                        );
                        Apache5HttpClientBuilderConfigurator apache5HttpClientBuilderConfigurator = (httpClientBuilder) -> {
                            return httpClientBuilder.setDefaultCredentialsProvider(credentialsProvider);
                        };

                        ClientConfig cc = new ClientConfig();
                        cc.register(apache5HttpClientBuilderConfigurator);
                        cc.connectorProvider(new Apache5ConnectorProvider());
                        Client client = ClientBuilder.newClient(cc);
                        ...
                    

                        HttpClient httpClient = new HttpClient(...);
                        ClientConfig clientConfig = new ClientConfig()
                            .connectorProvider(new JettyConnectorProvider())
                            .register(new JettyHttpClientSupplier(httpClient));
                        Client client = ClientBuilder.newClient(clientConfig);
                        ...
                    

Filtering requests and responses can provide useful lower-level concept focused on a certain independent aspect or domain that is decoupled from the application layer of building and sending requests, and processing responses. Filters can read/modify the request URI, headers and entity or read/modify the response status, headers and entity.

Jersey contains the following useful client-side filters (and features registering filters) that you may want to use in your applications:

Note that these features are provided by Jersey, but since they use and implement JAX-RS API, the features should be portable and run in any JAX-RS implementation, not just Jersey. See Chapter 10, Filters and Interceptors chapter for more information on filters and interceptors.

The underlying connections are opened for each request and closed after the response is received and entity is processed (entity is read). See the following example:

final WebTarget target = ... some web target
Response response = target.path("resource").request().get();
System.out.println("Connection is still open.");
System.out.println("string response: " + response.readEntity(String.class));
System.out.println("Now the connection is closed.");

If you don't read the entity, then you need to close the response manually by response.close(). Also if the entity is read into an InputStream (by response.readEntity(InputStream.class)), the connection stays open until you finish reading from the InputStream. In that case, the InputStream or the Response should be closed manually at the end of reading from InputStream.

In some cases you might need to inject some custom types into your client provider instance. JAX-RS types do not need to be injected as they are passed as arguments into API methods. Injections into client providers (filters, interceptor) are possible as long as the provider is registered as a class. If the provider is registered as an instance then runtime will not inject the provider. The reason is that this provider instance might be registered into multiple client configurations. For example one instance of ClientRequestFilter can be registered to two Clients.

To solve injection of a custom type into a client provider instance use InjectionManagerClientProvider to extract ServiceLocator which can return the required injection. The following example shows how to utilize InjectionManagerClientProvider:

public static class MyRequestFilter implements ClientRequestFilter {
    // this injection does not work as filter is registered as an instance:
    // @Inject
    // private MyInjectedService service;

    @Override
    public void filter(ClientRequestContext requestContext) throws IOException {
        // use InjectionManagerClientProvider to extract InjectionManager from request
        final InjectionManager injectionManager = InjectionManagerClientProvider.getInjectionManager(requestContext);

        // and ask for MyInjectedService:
        final MyInjectedService service = injectionManager.getInstance(MyInjectedService.class);

        final String name = service.getName();
        ...
    }
}

For more information see javadoc of InjectionManagerClientProvider (and javadoc of InjectionManagerProvider which supports common JAX-RS components).

This section describes how to setup SSL configuration on Jersey client (using JAX-RS API). The SSL configuration is setup in ClientBuilder. The client builder contains methods for definition of KeyStore, TrustStore or entire SslContext. See the following example:

SSLContext ssl = ... your configured SSL context;
Client client = ClientBuilder.newBuilder().sslContext(ssl).build();
Response response = client.target("https://example.com/resource").request().get();

The example above shows how to setup a custom SslContext to the ClientBuilder. Creating a SslContext can be more difficult as you might need to init instance properly with the protocol, KeyStore, TrustStore, etc. Jersey offers a utility SslConfigurator class that can be used to setup the SslContext. The SslConfigurator can be configured based on standardized system properties for SSL configuration, so for example you can configure the KeyStore file name using a environment variable javax.net.ssl.keyStore and SslConfigurator will use such a variable to setup the SslContext. See javadoc of SslConfigurator for more details. The following code shows how a SslConfigurator can be used to create a custom SSL context.

SslConfigurator sslConfig = SslConfigurator.newInstance()
        .trustStoreFile("./truststore_client")
        .trustStorePassword("secret-password-for-truststore")
        .keyStoreFile("./keystore_client")
        .keyPassword("secret-password-for-keystore");

SSLContext sslContext = sslConfig.createSSLContext();
Client client = ClientBuilder.newBuilder().sslContext(sslContext).build();

Note that you can also setup KeyStore and TrustStore directly on a ClientBuilder instance without wrapping them into the SslContext. However, if you setup a SslContext it will override any previously defined KeyStore and TrustStore settings. ClientBuilder also offers a method for defining a custom HostnameVerifier implementation. HostnameVerifier implementations are invoked when default host URL verification fails.

Currently the default connector provider HttpUrlConnectorProvider provides connectors based on HttpUrlConnection which implement support for SSL defined by JAX-RS configuration discussed in this example.

HttpAuthenticationFeature feature = HttpAuthenticationFeature.basic("user", "superSecretPassword");

HttpAuthenticationFeature feature = HttpAuthenticationFeature.basicBuilder()
    .nonPreemptive().credentials("user", "superSecretPassword").build();

HttpAuthenticationFeature feature = HttpAuthenticationFeature.basicBuilder().build();

Response response = client.target("http://localhost:8080/rest/homer/contact").request()
    .property(HTTP_AUTHENTICATION_BASIC_USERNAME, "homer")
    .property(HTTP_AUTHENTICATION_BASIC_PASSWORD, "p1swd745").get();

Suppose a case that the start of the request is to be logged and even measured. This can be done by ClientRequestFilter, which is usually invoked before the request is wired on the network. However, the filter may be called as a last of the filters in the chain. Sure, it can have the highest priority, but the other filters can have the very same priority! Some long-running operations can be performed before the measuring can actually start. Even worse, the filter may even be skipped from the chain by the previous #abortWith!

                /**
                * The method invoked before the request starts.
                * @param requestContext the request context shared with
                * ClientRequestFilter.
                */
                void beforeRequest(ClientRequestContext requestContext);
            

                /**
                * The method is invoked after a request when no
                * is thrown, or the Throwables are resolved
                * by previous PostInvocationInterceptor.
                *
                * @param requestContext the request context.
                * @param responseContext the response context
                * of the original Response or response context
                * defined by the new resolving Response.
                */
                void afterRequest(ClientRequestContext requestContext, ClientResponseContext responseContext);

                /**
                * The method is invoked after a Throwable is caught
                * during the client request chain processing.
                *
                * @param requestContext the request context.
                * @param exceptionContext the context available to handle the
                * caught Throwables.
                */
                void onException(ClientRequestContext requestContext, ExceptionContext exceptionContext);
            

                String response = ClientBuilder.newClient().target("path")
                    .register(new PreInvocationInterceptor() {
                        @Override
                        public void beforeRequest(ClientRequestContext requestContext) {
                            startTime = System.currentTimeMillis();
                        }
                    })
                    .register(new PostInvocationInterceptor() {
                        @Override
                        public void afterRequest(ClientRequestContext requestContext, ClientResponseContext responseContext) {
                            logDuration(System.currentTimeMillis() - startTime);
                        }
                        @Override
                        public void onException(ClientRequestContext requestContext, ExceptionContext exceptionContext) {
                            logDuration(System.currentTimeMillis() - startTime);
                        }
                    })
                    .request().get().readEntity(String.class);
            

InvocationBuilderListener is an interface that is inspired by Microprofile REST Client RestClientBuilderListener and it contains a single method:

            /**
            * Whenever an Invocation.Builder is created, (i.e. when
            * WebTarget#request() is called, this method would be invoked.
            *
            * @param context the updated InvocationBuilderContext.
            */
            void onNewBuilder(InvocationBuilderContext context);
        

InvocationBuilderContext a subset of methods of the Invocation.Builder. It can be used to call the default values of the Invocation.Builder. Since it is invoked at the time Invocation.Builder is instantiated, any consequent calls of the Invocation.Builder‘s methods will replace the defaults set by the InvocationBuilderListener. For instance, if all the HTTP requests should contain a custom HTTP header, there can be created a feature that would be registered on the client:

            public static class MyFeature implements Feature {
                @Override
                public boolean configure(FeatureContext context) {
                    context.register(
                        (InvocationBuilderListener)(l)->
                        l.getHeaders().add("MY_HEADER", "MY_VALUE")
                    );
                    return true;
                }
            }
        

This section describes support of Expect:100-continue in Jersey client using Expect100Continue feature. Jersey client supports given header for default JDK HTTP connector only.

Jersey client Expect100Continue feature

Since Jersey 2.32 it is possible to send Expect:100-continue header from Jersey client. Feature shall be registered in client using (for example)

                target(RESOURCE_PATH).register(Expect100ContinueFeature.basic());
            

Note that registration can be done in several ways: with basic settings, and with custom settings:

                target(RESOURCE_PATH).register(Expect100ContinueFeature.withCustomThreshold(100L));
            

Basic registration means that default sending threshold will be used. Value of the default threshold is

                DEFAULT_EXPECT_100_CONTINUE_THRESHOLD_SIZE = 65536L;
            

Threshold is used to determine allowed size of request after which 100-continue header shall be sent before sending request itself.

Environment properties configuration

Previous paragraph described programmatic way of configuration. However the Expect100Continue feature can be configured using environment variables as well.

Since Jersey client can be influenced through environment variables, there are two variables which come since Jersey 2.32:

                -Djersey.config.client.request.expect.100.continue.processing=true/false
                -Djersey.config.client.request.expect.100.continue.threshold.size=12345
            

First variable can be used to forbid the Expect (100-continue) header be sent at all even though it is registered as described in the previous paragraph. If this property is not provided (or true) and the Expect100Continue feature is registered, sending of the Expect header is enabled.

The second property defines (or modifies) threshold size. So, if the Expect100Continue feature is registered using basic (default threshold size) parameters, value of the threshold can be modified using this property. This is valid for custom threshold as well - when the Expect100Continue feature is registered using withCustomThreshold method its value can be modified anyway by the environment property jersey.config.client.request.expect.100.continue.threshold.size.

Reactive Client API is part of the JAX-RS specification since version 2.1.

When you compare synchronous invocation of HTTP calls ( Example 6.4, “Synchronous invocation of HTTP requests”)

Response response = ClientBuilder.newClient()
        .target("http://example.com/resource")
        .request()
        .get();

with asynchronous invocation (Example 6.5, “Asynchronous invocation of HTTP requests”)

Future<Response> response = ClientBuilder.newClient()
        .target("http://example.com/resource")
        .request()
        .async()
        .get();

it is apparent how to pretty conveniently modify the way how a request is invoked (from sync to async) only by calling async method on an Invocation.Builder.

Naturally, it'd be nice to copy the same pattern to allow invoking requests in a reactive way. Just instead of async you'd call rx on an extension of Invocation.Builder, like in Example 6.6, “Reactive invocation of HTTP requests”.

CompletionStage<Response> response = ClientBuilder.newClient()
        .target("http://example.com/resource")
        .request()
        .rx()
        .get();

The first reactive interface in the invocation chain is RxInvoker which is very similar to SyncInvoker and AsyncInvoker. It contains all methods present in the two latter JAX-RS interfaces but the RxInvoker interface is more generic, so that it can be extended and used in particular implementations taking advantage of various reactive libraries. Extending this new interface in a particular implementation also preserves type safety which means that you're not loosing type information when a HTTP method call returns an object that you want to process further.

The method "rx()" in the example above is perfect example of that principle. It returns CompletionStageRxInvoker, which extends RxInvoker.

As a user of the Reactive Client API you only need to keep in mind that you won't be working with RxInvoker directly. You'd rather be working with an extension of this interface created for a particular implementation and you don't need to be bothered much with why are things designed the way they are.

The important thing to notice here is that an extension of RxInvoker holds the type information and the Reactive Client needs to know about this type to properly propagate it among the method calls you'll be making. This is the reason why other interfaces (described bellow) are parametrized with this type.

In order to extend the API to be used with other reactive frameworks, RxInvokerProvider needs to be registered into the Client runtime:

Client client = ClientBuilder.newClient();
client.register(RxFlowableInvokerProvider.class);

Flowable<String> responseFlowable =
        client.target("http://jersey.java.net")
              .request()
              .rx(RxFlowableInvoker.class)
              .get(String.class);

String responseString = responseFlowable.blockingFirst();

There are already some available reactive (or reactive-like) libraries out there and Jersey brings support for some of them out of the box. Jersey currently supports:

// New Client
Client client = ClientBuilder.newClient();
client.register(RxObservableInvokerProvider.class);

Observable<Response> observable = RxObservable.newClient()
                                                    .target("http://example.com/resource")
                                                    .request()
                                                    .rx(RxObservableInvoker.class)
                                                    .get();

<dependency>
    <groupId>org.glassfish.jersey.ext.rx</groupId>
    <artifactId>jersey-rx-client-rxjava</artifactId>
    <version>2.38-SNAPSHOT</version>
</dependency>

// New Client
Client client = ClientBuilder.newClient();
client.register(RxFlowableInvokerProvider.class);

Flowable<Response> observable = RxObservable.newClient()
                            .target("http://example.com/resource")
                            .request()
                            .rx(RxFlowableInvoker.class)
                            .get();
                        

<dependency>
    <groupId>org.glassfish.jersey.ext.rx</groupId>
    <artifactId>jersey-rx-client-rxjava2</artifactId>
    <version>2.38-SNAPSHOT</version>
</dependency>

// New Client
Client client = ClientBuilder.newClient();
client.register(RxListenableFutureInvokerProvider.class);

ListenableFuture<Response> response = client.target("http://jersey.java.net")
                                            .request()
                                            .rx(RxListenableFutureInvoker.class)
                                            .get();

<dependency>
    <groupId>org.glassfish.jersey.ext.rx</groupId>
    <artifactId>jersey-rx-client-guava</artifactId>
    <version>2.38-SNAPSHOT</version>
</dependency>

In case you want to bring support for some other library providing Reactive Programming Model into your application you can extend functionality of Reactive JAX-RS Client by implementing RxInvokerProvider, registering that implementation into the client runtime and then using rx(Class<T>) in your code.

public interface CompletionStageRxInvoker extends RxInvoker<CompletionStage> {
    @Override
    public CompletionStage<Response> get();

    @Override
    public <T> CompletionStage<T> get(Class<T> responseType);

    // ...
}

public static class CompletionStageRxInvokerProvider implements RxInvokerProvider<CompletionStageRxInvoker> {
    @Override
    public boolean isProviderFor(Class<?%gt; clazz) {
        return CompletionStage.class.equals(clazz);
    }

    @Override
    public CompletionStageRxInvoker getRxInvoker(SyncInvoker syncInvoker, ExecutorService executorService) {
        return new CompletionStageRxInvoker() {
            // ...
        };
    }
}

Client client = ClientBuilder.newClient();
// register custom RxInvokerProvider
client.register(CompletionStageRxInvokerProvider.class);

CompletionStage<Response> response =
        client.target("http://jersey.java.net")
              .request()
              .rx(CompletionStageRxInvoker.class)
              // Now we have an instance of CompletionStageRxInvoker returned from our registered RxInvokerProvider,
              // which is CompletionStageRxInvokerProvider in this particular scenario.
              .get();

Previous sections on @Produces and @Consumes annotations referred to media type of an entity representation. Examples above depicted resource methods that could consume and/or produce String Java type for a number of different media types. This approach is easy to understand and relatively straightforward when applied to simple use cases.

To cover also other cases, handling non-textual data for example or handling data stored in the file system, etc., JAX-RS implementations are required to support also other kinds of media type conversions where additional, non-String, Java types are being utilized. Following is a short listing of the Java types that are supported out of the box with respect to supported media type:

Unlike method parameters that are associated with the extraction of request parameters, the method parameter associated with the representation being consumed does not require annotating. In other words the representation (entity) parameter does not require a specific 'entity' annotation. A method parameter without an annotation is an entity. A maximum of one such unannotated method parameter may exist since there may only be a maximum of one such representation sent in a request.

The representation being produced corresponds to what is returned by the resource method. For example JAX-RS makes it simple to produce images that are instance of File as follows:

@GET
@Path("/images/{image}")
@Produces("image/*")
public Response getImage(@PathParam("image") String image) {
  File f = new File(image);

  if (!f.exists()) {
    throw new WebApplicationException(404);
  }

  String mt = new MimetypesFileTypeMap().getContentType(f);
  return Response.ok(f, mt).build();
}

The File type can also be used when consuming a representation (request entity). In that case a temporary file will be created from the incoming request entity and passed as a parameter to the resource method.

The Content-Type response header (if not set programmatically as described in the next section) will be automatically set based on the media types declared by @Produces annotation. Given the following method, the most acceptable media type is used when multiple output media types are allowed:

@GET
@Produces({"application/xml", "application/json"})
public String doGetAsXmlOrJson() {
  ...
}

If application/xml is the most acceptable media type defined by the request (e.g. by header Accept: application/xml), then the Content-Type response header will be set to application/xml.

Sometimes it is necessary to return additional information in response to a HTTP request. Such information may be built and returned using Response and Response.ResponseBuilder. For example, a common RESTful pattern for the creation of a new resource is to support a POST request that returns a 201 (Created) status code and a Location header whose value is the URI to the newly created resource. This may be achieved as follows:

@POST
@Consumes("application/xml")
public Response post(String content) {
  URI createdUri = ...
  create(content);
  return Response.created(createdUri).build();
}

In the above no representation produced is returned, this can be achieved by building an entity as part of the response as follows:

@POST
@Consumes("application/xml")
public Response post(String content) {
  URI createdUri = ...
  String createdContent = create(content);
  return Response.created(createdUri).entity(Entity.text(createdContent)).build();
}

Response building provides other functionality such as setting the entity tag and last modified date of the representation.

Previous section shows how to return HTTP responses, that are built up programmatically. It is possible to use the very same mechanism to return HTTP errors directly, e.g. when handling exceptions in a try-catch block. However, to better align with the Java programming model, JAX-RS allows to define direct mapping of Java exceptions to HTTP error responses.

The following example shows throwing CustomNotFoundException from a resource method in order to return an error HTTP response to the client:

@Path("items/{itemid}/")
public Item getItem(@PathParam("itemid") String itemid) {
  Item i = getItems().get(itemid);
  if (i == null) {
    throw new CustomNotFoundException("Item, " + itemid + ", is not found");
  }

  return i;
}

This exception is an application specific exception that extends WebApplicationException and builds a HTTP response with the 404 status code and an optional message as the body of the response:

public class CustomNotFoundException extends WebApplicationException {

  /**
  * Create a HTTP 404 (Not Found) exception.
  */
  public CustomNotFoundException() {
    super(Responses.notFound().build());
  }

  /**
  * Create a HTTP 404 (Not Found) exception.
  * @param message the String that is the entity of the 404 response.
  */
  public CustomNotFoundException(String message) {
    super(Response.status(Responses.NOT_FOUND).
    entity(message).type("text/plain").build());
  }
}

In other cases it may not be appropriate to throw instances of WebApplicationException, or classes that extend WebApplicationException, and instead it may be preferable to map an existing exception to a response. For such cases it is possible to use a custom exception mapping provider. The provider must implement the ExceptionMapper<E extends Throwable> interface. For example, the following maps the EntityNotFoundException to a HTTP 404 (Not Found) response:

@Provider
public class EntityNotFoundMapper implements ExceptionMapper<javax.persistence.EntityNotFoundException> {
  public Response toResponse(javax.persistence.EntityNotFoundException ex) {
    return Response.status(404).
      entity(ex.getMessage()).
      type("text/plain").
      build();
  }
}

The above class is annotated with @Provider, this declares that the class is of interest to the JAX-RS runtime. Such a class may be added to the set of classes of the Application instance that is configured. When an application throws an EntityNotFoundException the toResponse method of the EntityNotFoundMapper instance will be invoked.

Jersey supports extension of the exception mappers. These extended mappers must implement the org.glassfish.jersey.spi.ExtendedExceptionMapper interface. This interface additionally defines method isMappable(Throwable) which will be invoked by the Jersey runtime when exception is thrown and this provider is considered as mappable based on the exception type. Using this method the provider can reject mapping of the exception before the method toResponse is invoked. The provider can for example check the exception parameters and based on them return false and let other provider to be chosen for the exception mapping.

Conditional GETs are a great way to reduce bandwidth, and potentially improve on the server-side performance, depending on how the information used to determine conditions is calculated. A well-designed web site may for example return 304 (Not Modified) responses for many of static images it serves.

JAX-RS provides support for conditional GETs using the contextual interface Request.

The following example shows conditional GET support:

public SparklinesResource(
  @QueryParam("d") IntegerList data,
  @DefaultValue("0,100") @QueryParam("limits") Interval limits,
  @Context Request request,
  @Context UriInfo ui) {
  if (data == null) {
    throw new WebApplicationException(400);
  }

  this.data = data;
  this.limits = limits;

  if (!limits.contains(data)) {
    throw new WebApplicationException(400);
  }

  this.tag = computeEntityTag(ui.getRequestUri());

  if (request.getMethod().equals("GET")) {
    Response.ResponseBuilder rb = request.evaluatePreconditions(tag);
    if (rb != null) {
      throw new WebApplicationException(rb.build());
    }
  }
}

The constructor of the SparklinesResource root resource class computes an entity tag from the request URI and then calls the request.evaluatePreconditions with that entity tag. If a client request contains an If-None-Match header with a value that contains the same entity tag that was calculated then the evaluatePreconditions returns a pre-filled out response, with the 304 status code and entity tag set, that may be built and returned. Otherwise, evaluatePreconditions returns null and the normal response can be returned.

Notice that in this example the constructor of a resource class is used to perform actions that may otherwise have to be duplicated to be invoked for each resource method. The life cycle of resource classes is per-request which means that the resource instance is created for each request and therefore can work with request parameters and for example make changes to the request processing by throwing an exception as it is shown in this example.

Entity payload, if present in an received HTTP message, is passed to Jersey from an I/O container as an input stream. The stream may, for example, contain data represented as a plain text, XML or JSON document. However, in many JAX-RS components that process these inbound data, such as resource methods or client responses, the JAX-RS API user can access the inbound entity as an arbitrary Java object that is created from the content of the input stream based on the representation type information. For example, an entity created from an input stream that contains data represented as a XML document, can be converted to a custom JAXB bean. Similar concept is supported for the outbound entities. An entity returned from the resource method in the form of an arbitrary Java object can be serialized by Jersey into a container output stream as a specified representation. Of course, while JAX-RS implementations do provide default support for most common combinations of Java type and it's respective on-the-wire representation formats, JAX-RS implementations do not support the conversion described above for any arbitrary Java type and any arbitrary representation format by default. Instead, a generic extension concept is exposed in JAX-RS API to allow application-level customizations of this JAX-RS runtime to support for entity conversions. The JAX-RS extension API components that provide the user-level extensibility are typically referred to by several terms with the same meaning, such as entity providers, message body providers, message body workers or message body readers and writers. You may find all these terms used interchangeably throughout the user guide and they all refer to the same concept.

In JAX-RS extension API (or SPI - service provider interface, if you like) the concept is captured in 2 interfaces. One for handling inbound entity representation-to-Java de-serialization - MessageBodyReader<T> and the other one for handling the outbound entity Java-to-representation serialization - MessageBodyWriter<T>. A MessageBodyReader<T>, as the name suggests, is an extension that supports reading the message body representation from an input stream and converting the data into an instance of a specific Java type. A MessageBodyWriter<T> is then responsible for converting a message payload from an instance of a specific Java type into a specific representation format that is sent over the wire to the other party as part of an HTTP message exchange. Both of these providers can be used to provide message payload serialization and de-serialization support on the server as well as the client side. A message body reader or writer is always used whenever a HTTP request or response contains an entity and the entity is either requested by the application code (e.g. injected as a parameter of JAX-RS resource method or a response entity read on the client from a Response) or has to be serialized and sent to the other party (e.g. an instance returned from a JAX-RS resource method or a request entity sent by a JAX-RS client).

A best way how to learn about entity providers is to walk through an example of writing one. Therefore we will describe here the process of implementing a custom MessageBodyWriter<T> and MessageBodyReader<T> using a practical example. Let's first setup the stage by defining a JAX-RS resource class for the server side story of our application.

@Path("resource")
public class MyResource {
    @GET
    @Produces("application/xml")
    public MyBean getMyBean() {
        return new MyBean("Hello World!", 42);
    }

    @POST
    @Consumes("application/xml")
    public String postMyBean(MyBean myBean) {
        return myBean.anyString;
    }
}

The resource class defines GET and POST resource methods. Both methods work with an entity that is an instance of MyBean.

The MyBean class is defined in the next example:

@XmlRootElement
public class MyBean {
    @XmlElement
    public String anyString;
    @XmlElement
    public int anyNumber;

    public MyBean(String anyString, int anyNumber) {
        this.anyString = anyString;
        this.anyNumber = anyNumber;
    }

    // empty constructor needed for deserialization by JAXB
    public MyBean() {
    }

    @Override
    public String toString() {
        return "MyBean{" +
            "anyString='" + anyString + '\'' +
            ", anyNumber=" + anyNumber +
            '}';
    }
}

@Produces("application/xml")
public class MyBeanMessageBodyWriter implements MessageBodyWriter<MyBean> {

    @Override
    public boolean isWriteable(Class<?> type, Type genericType,
                               Annotation[] annotations, MediaType mediaType) {
        return type == MyBean.class;
    }

    @Override
    public long getSize(MyBean myBean, Class<?> type, Type genericType,
                        Annotation[] annotations, MediaType mediaType) {
        // deprecated by JAX-RS 2.0 and ignored by Jersey runtime
        return -1;
    }

    @Override
    public void writeTo(MyBean myBean,
                        Class<?> type,
                        Type genericType,
                        Annotation[] annotations,
                        MediaType mediaType,
                        MultivaluedMap<String, Object> httpHeaders,
                        OutputStream entityStream)
                        throws IOException, WebApplicationException {

        try {
            JAXBContext jaxbContext = JAXBContext.newInstance(MyBean.class);

            // serialize the entity myBean to the entity output stream
            jaxbContext.createMarshaller().marshal(myBean, entityStream);
        } catch (JAXBException jaxbException) {
            throw new ProcessingException(
                "Error serializing a MyBean to the output stream", jaxbException);
        }
    }
}

@Path("resource")
public static class AnnotatedResource {

    @GET
    public Response get() {
        Annotation annotation = AnnotatedResource.class
                            .getAnnotation(Path.class);
        return Response.ok()
                .entity("Entity", new Annotation[] {annotation}).build();
    }
}

WebTarget webTarget = // initialize web target to the context root
            // of example application
Response response = webTarget.path("resource")
                        .request(MediaType.APPLICATION_XML).get();
System.out.println(response.getStatus());
String myBeanXml = response.readEntity(String.class);
System.out.println(myBeanXml);

200
<?xml version="1.0" encoding="UTF-8" standalone="yes"?><myBean>
<anyString>Hello World!</anyString><anyNumber>42</anyNumber></myBean>

public static class MyBeanMessageBodyReader
        implements MessageBodyReader<MyBean> {

@Override
public boolean isReadable(Class<?> type, Type genericType,
    Annotation[] annotations, MediaType mediaType) {
    return type == MyBean.class;
}

@Override
public MyBean readFrom(Class<MyBean> type,
    Type genericType,
    Annotation[] annotations, MediaType mediaType,
    MultivaluedMap<String, String> httpHeaders,
    InputStream entityStream)
        throws IOException, WebApplicationException {

    try {
        JAXBContext jaxbContext = JAXBContext.newInstance(MyBean.class);
        MyBean myBean = (MyBean) jaxbContext.createUnmarshaller()
            .unmarshal(entityStream);
        return myBean;
    } catch (JAXBException jaxbException) {
        throw new ProcessingException("Error deserializing a MyBean.",
            jaxbException);
    }
}
}

final MyBean myBean = new MyBean("posted MyBean", 11);
Response response = webTarget.path("resource").request("application/xml")
        .post(Entity.entity(myBean, "application/xml"));

System.out.println(response.getStatus());
final String responseEntity = response.readEntity(String.class);
System.out.println(responseEntity);

200
posted MyBean

Client client = ClientBuilder.newBuilder()
    .register(MyBeanMessageBodyReader.class).build();

Response response = client.target("http://example/comm/resource")
    .request(MediaType.APPLICATION_XML).get();
System.out.println(response.getStatus());
MyBean myBean = response.readEntity(MyBean.class);
System.out.println(myBean);

200
MyBean{anyString='Hello World!', anyNumber=42}

Usually there are many entity providers registered on the server or client side (be default there must be at least providers mandated by the JAX-RS specification, such as providers for primitive types, byte array, JAXB beans, etc.). JAX-RS defines an algorithm for selecting the most suitable provider for entity processing. This algorithm works with information such as entity Java type and on-the-wire media type representation of entity, and searches for the most suitable entity provider from the list of available providers based on the supported media type declared on each provider (defined by @Produces or @Consumes on the provider class) as well as based on the generic type declaration of the available providers. When a list of suitable candidate entity providers is selected and sorted based on the rules defined in JAX-RS specification, a JAX-RS runtime then it invokes isReadable or isWriteable method respectively on each provider in the list until a first provider is found that returns true. This provider is then used to process the entity.

The following steps describe the algorithm for selecting a MessageBodyWriter<T> (extracted from JAX-RS with little modifications). The steps refer to the previously discussed example application. The MessageBodyWriter<T> is searched for purpose of deserialization of MyBean entity returned from the method getMyBean. So, type is MyBean and media type "application/xml". Let's assume the runtime contains also registered providers, namely:

The algorithm executed by a JAX-RS runtime to select a proper MessageBodyWriter<T> implementation is illustrated in Procedure 8.1, “MessageBodyWriter<T> Selection Algorithm”.

jersey.config.workers.legacyOrdering=true

The algorithm for selection of MessageBodyReader<T> is similar, including the incompatibility between JAX-RS 2.0 and JAX-RS 1.x and the property to workaround it. The algorithm is defined as follows:

In case you need to directly work with JAX-RS entity providers, for example to serialize an entity in your resource method, filter or in a composite entity provider, you would need to perform quite a lot of steps. You would need to choose the appropriate MessageBodyWriter<T> based on the type, media type and other parameters. Then you would need to instantiate it, check it by isWriteable method and basically perform all the steps that are normally performed by Jersey (see Procedure 8.2, “MessageBodyReader<T> Selection Algorithm”).

To remove this burden from developers, Jersey exposes a proprietary public API that simplifies the manipulation of entity providers. The API is defined by MessageBodyWorkers interface and Jersey provides an implementation that can be injected using the @Context injection annotation. The interface declares methods for selection of most appropriate MessageBodyReader<T> and MessageBodyWriter<T> based on the rules defined in JAX-RS spec, methods for writing and reading entity that ensure proper and timely invocation of interceptors and other useful methods.

See the following example of usage of MessageBodyWorkers.

@Path("workers")
public static class WorkersResource {

    @Context
    private MessageBodyWorkers workers;

    @GET
    @Produces("application/xml")
    public String getMyBeanAsString() {

        final MyBean myBean = new MyBean("Hello World!", 42);

        // buffer into which myBean will be serialized
        ByteArrayOutputStream baos = new ByteArrayOutputStream();

        // get most appropriate MBW
        final MessageBodyWriter<MyBean> messageBodyWriter =
                workers.getMessageBodyWriter(MyBean.class, MyBean.class,
                        new Annotation[]{}, MediaType.APPLICATION_XML_TYPE);

        try {
            // use the MBW to serialize myBean into baos
            messageBodyWriter.writeTo(myBean,
                MyBean.class, MyBean.class, new Annotation[] {},
                MediaType.APPLICATION_XML_TYPE, new MultivaluedHashMap<String, Object>(),
                baos);
        } catch (IOException e) {
            throw new RuntimeException(
                "Error while serializing MyBean.", e);
        }

        final String stringXmlOutput = baos.toString();
        // stringXmlOutput now contains XML representation:
        // "<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
        // <myBean><anyString>Hello World!</anyString>
        // <anyNumber>42</anyNumber></myBean>"

        return stringXmlOutput;
    }
}

In the example a resource injects MessageBodyWorkers and uses it for selection of the most appropriate MessageBodyWriter<T>. Then the writer is utilized to serialize the entity into the buffer as XML document. The String content of the buffer is then returned. This will cause that Jersey will not use MyBeanMessageBodyWriter to serialize the entity as it is already in the String type (MyBeanMessageBodyWriter does not support String). Instead, a simple String-based MessageBodyWriter<T> will be chosen and it will only serialize the String with XML to the output entity stream by writing out the bytes of the String.

Of course, the code in the example does not bring any benefit as the entity could have been serialized by MyBeanMessageBodyWriter by Jersey as in previous examples; the purpose of the example was to show how to use MessageBodyWorkers in a resource method.

Jersey internally contains entity providers for these types with combination of media types (in brackets):

For other media type supported in jersey please see the Chapter 9, Support for Common Media Type Representations which describes additional Jersey entity provider extensions for serialization to JSON, XML, serialization of collections, Multi Part and others.

Jersey JSON support comes as a set of extension modules where each of these modules contains an implementation of a Feature that needs to be registered into your Configurable instance (client/server). There are multiple frameworks that provide support for JSON processing and/or JSON-to-Java binding. The modules listed below provide support for JSON representations by integrating the individual JSON frameworks into Jersey. At present, Jersey integrates with the following modules to provide JSON support:

@XmlRootElement
public class MyJaxbBean {
    public String name;
    public int age;

    public MyJaxbBean() {} // JAXB needs this

    public MyJaxbBean(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

@GET
@Produces("application/json")
public MyJaxbBean getMyBean() {
    return new MyJaxbBean("Agamemnon", 32);
}

{"name":"Agamemnon", "age":"32"}

@XmlRootElement
public class MyJaxbBean {

    @XmlElement(name="king")
    public String name;

    @XmlTransient
    public int age;

    // several lines removed
}

MyJaxbBean myBean = new MyJaxbBean("Agamemnon", 32);

JsonObject myObject = Json.createObjectBuilder()
        .add("name", "Agamemnon")
        .add("age", 32)
        .build();

JSONObject myObject = new JSONObject();
try {
    myObject.put("name", "Agamemnon");
    myObject.put("age", 32);
} catch (JSONException ex) {
    LOGGER.log(Level.SEVERE, "Error ...", ex);
}

<dependency>
    <groupId>org.glassfish.jersey.media</groupId>
    <artifactId>jersey-media-moxy</artifactId>
    <version>2.38-SNAPSHOT</version>
</dependency>

final Map<String, String> namespacePrefixMapper = new HashMap<String, String>();
namespacePrefixMapper.put("http://www.w3.org/2001/XMLSchema-instance", "xsi");

final MoxyJsonConfig configuration = new MoxyJsonConfig()
        .setNamespacePrefixMapper(namespacePrefixMapper)
        .setNamespaceSeparator(':');
                        

final Map<String, String> namespacePrefixMapper = new HashMap<String, String>();
namespacePrefixMapper.put("http://www.w3.org/2001/XMLSchema-instance", "xsi");

final MoxyJsonConfig moxyJsonConfig = MoxyJsonConfig()
            .setNamespacePrefixMapper(namespacePrefixMapper)
            .setNamespaceSeparator(':');

final ContextResolver<MoxyJsonConfig> jsonConfigResolver = moxyJsonConfig.resolver();

new ResourceConfig()
                            .property(MarshallerProperties.JSON_NAMESPACE_SEPARATOR, ".")
                            // further configuration

final Client client = ClientBuilder.newBuilder()
        // The line below that registers MOXy feature can be
        // omitted if FEATURE_AUTO_DISCOVERY_DISABLE is
        // not disabled.
        .register(MoxyJsonFeature.class)
        .register(jsonConfigResolver)
        .build();

// Create JAX-RS application.
final Application application = new ResourceConfig()
        .packages("org.glassfish.jersey.examples.jsonmoxy")
        // The line below that registers MOXy feature can be
        // omitted if FEATURE_AUTO_DISCOVERY_DISABLE is
        // not disabled.
        .register(MoxyJsonFeature.class)
        .register(jsonConfigResolver);

<dependency>
    <groupId>org.glassfish.jersey.media</groupId>
    <artifactId>jersey-media-json-processing</artifactId>
    <version>2.38-SNAPSHOT</version>
</dependency>

ClientBuilder.newClient(new ClientConfig()
        // The line below that registers JSON-Processing feature can be
        // omitted if FEATURE_AUTO_DISCOVERY_DISABLE is not disabled.
        .register(JsonProcessingFeature.class)
        .property(JsonGenerator.PRETTY_PRINTING, true)
);

// Create JAX-RS application.
final Application application = new ResourceConfig()
        // The line below that registers JSON-Processing feature can be
        // omitted if FEATURE_AUTO_DISCOVERY_DISABLE is not disabled.
        .register(JsonProcessingFeature.class)
        .packages("org.glassfish.jersey.examples.jsonp")
        .property(JsonGenerator.PRETTY_PRINTING, true);

<dependency>
    <groupId>org.glassfish.jersey.media</groupId>
    <artifactId>jersey-media-json-jackson</artifactId>
    <version>2.38-SNAPSHOT</version>
</dependency>

<dependency>
    <groupId>org.glassfish.jersey.media</groupId>
    <artifactId>jersey-media-json-jackson1</artifactId>
    <version>2.38-SNAPSHOT</version>
</dependency>

@Provider
public class MyObjectMapperProvider implements ContextResolver<ObjectMapper> {

    final ObjectMapper defaultObjectMapper;

    public MyObjectMapperProvider() {
        defaultObjectMapper = createDefaultMapper();
    }

    @Override
    public ObjectMapper getContext(Class<?> type) {
            return defaultObjectMapper;
        }
    }

    private static ObjectMapper createDefaultMapper() {
        final ObjectMapper result = new ObjectMapper();
        result.configure(Feature.INDENT_OUTPUT, true);

        return result;
    }

    // ...
}

final Client client = ClientBuilder.newBuilder()
        .register(MyObjectMapperProvider.class)  // No need to register this provider if no special configuration is required.
        .register(JacksonFeature.class)
        .build();

// Create JAX-RS application.
final Application application = new ResourceConfig()
        .packages("org.glassfish.jersey.examples.jackson")
        .register(MyObjectMapperProvider.class)  // No need to register this provider if no special configuration is required.
        .register(JacksonFeature.class);

<dependency>
    <groupId>org.glassfish.jersey.media</groupId>
    <artifactId>jersey-media-json-jettison</artifactId>
    <version>2.38-SNAPSHOT</version>
</dependency>

@XmlRootElement
public class Address {
    public String street;
    public String town;

    public Address(){}

    public Address(String street, String town) {
        this.street = street;
        this.town = town;
    }
}

@XmlRootElement
public class Contact {

    public int id;
    public String name;
    public List<Address> addresses;

    public Contact() {};

    public Contact(int id, String name, List<Address> addresses) {
        this.name = name;
        this.id = id;
        this.addresses =
            (addresses != null) ? new LinkedList<Address>(addresses) : null;
    }
}

Address[] addresses = {new Address("Long Street 1", "Short Village")};
Contact contact = new Contact(2, "Bob", Arrays.asList(addresses));

...
@XmlElement(namespace="http://example.com")
public int id;
...

Map<String,String> ns2json = new HashMap<String, String>();
ns2json.put("http://example.com", "example");
context = new JettisonJaxbContext(
    JettisonConfig.mappedJettison().xml2JsonNs(ns2json).build(),
    types);

{
   "contact":{
      "example.id":2,
      "name":"Bob",
      "addresses":{
         "street":"Long Street 1",
         "town":"Short Village"
      }
   }
}

context = new JettisonJaxbContext(
    JettisonConfig.mappedJettison().serializeAsArray("name").build(),
    types);

{
   "contact":{
      ...
      "name":["Bob"],
      ...
   }
}

JettisonConfig.badgerFish().build()

{
   "contact":{
      "id":{
         "$":"2"
      },
      "name":{
         "$":"Bob"
      },
      "addresses":{
         "street":{
            "$":"Long Street 1"
         },
         "town":{
            "$":"Short Village"
         }
      }
   }
}

@Provider
public class JaxbContextResolver implements ContextResolver<JAXBContext> {

    private final JAXBContext context;
    private final Set<Class<?>> types;
    private final Class<?>[] cTypes = {Flights.class, FlightType.class, AircraftType.class};

    public JaxbContextResolver() throws Exception {
        this.types = new HashSet<Class<?>>(Arrays.asList(cTypes));
        this.context = new JettisonJaxbContext(JettisonConfig.DEFAULT, cTypes);
    }

    @Override
    public JAXBContext getContext(Class<?> objectType) {
        return (types.contains(objectType)) ? context : null;
    }
}

final Client client = ClientBuilder.newBuilder()
        .register(JaxbContextResolver.class)  // No need to register this provider if no special configuration is required.
        .register(JettisonFeature.class)
        .build();

// Create JAX-RS application.
final Application application = new ResourceConfig()
        .packages("org.glassfish.jersey.examples.jettison")
        .register(JaxbContextResolver.class)  // No need to register this provider if no special configuration is required.
        .register(JettisonFeature.class);

@GET
@JSONP
@Produces({"application/json", "application/javascript"})
public JaxbBean getSimpleJSONP() {
    return new JaxbBean("jsonp");
}

@XmlRootElement
public class JaxbBean {

    private String value;

    public JaxbBean() {}

    public JaxbBean(final String value) {
        this.value = value;
    }

    public String getValue() {
        return value;
    }

    public void setValue(final String value) {
        this.value = value;
    }
}

callback({
    "value" : "jsonp",
})

@GET
@Produces({"application/json", "application/javascript"})
@JSONP(callback = "eval", queryParam = "jsonpCallback")
public JaxbBean getSimpleJSONP() {
    return new JaxbBean("jsonp");
}

curl -X GET http://localhost:8080/jsonp

eval({
    "value" : "jsonp",
})

curl -X GET http://localhost:8080/jsonp?jsonpCallback=alert

alert({
    "value" : "jsonp",
})

<dependency>
    <groupId>org.glassfish.jersey.media</groupId>
    <artifactId>jersey-media-json-binding</artifactId>
    <version>2.38-SNAPSHOT</version>
</dependency>