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Refer to Environment Variables in POM

· 2 min read
Jack

Environment Variables​

To refer to environment variables from the pom.xml, we can use the ${env.VARIABLE_NAME} syntax.

For instance, let's use it to externalize the Java version in the build process:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.1</version>
            <configuration>
                <source>${env.JAVA_VERSION}</source>
                <target>${env.JAVA_VERSION}</target>
            </configuration>
        </plugin>
    </plugins>
</build>

We should remember to pass the Java version information via environment variables. If we fail to do so, then we won't be able to build the project.

To run the Maven goals or phases against such a build file, we should first export the environment variable. For instance

export JAVA_VERSION=17
mvn clean package

In order to provide a default when the JAVA_VERSION environment variable is missing we can use a Maven profile:

<profiles>
    <profile>
        <id>default-java</id>
        <activation>
            <property>
                <name>!env.JAVA_VERSION</name>
            </property>
        </activation>
        <build>
            <plugins>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <version>3.8.1</version>
                    <configuration>
                        <source>1.8</source>
                        <target>1.8</target>
                    </configuration>
                </plugin>
            </plugins>
        </build>
    </profile>
</profiles>

As shown above, we're creating a profile and making it active only if the JAVA_VERSION environment variable is missing (!env.JAVA_VERSION part). If that happens, then this new plugin definition will override the existing one.