How to set a specific Java version in Maven?

Setting Java version via JAVA_HOME

Maven uses the JAVA_HOME environment variable to determine which Java version to employ. By setting this variable, you control which JDK Maven picks up. Here's how you do it:

export JAVA_HOME=/usr/lib/jvm/java-11-oracle  # On Unix systems
set JAVA_HOME=C:\Program Files\Java\jdk-11.0.1 # On Windows
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Don't forget to revert JAVA_HOME once done or James Gosling might come to your dreams ~ holding a cup of Java.

Customizing the Maven script

You can directly edit the mvn, mvn.bat, or mvn.cmd scripts, specifically setting the JAVA_HOME right there. It's like ordering a coffee directly from the counter, skipping the queue.

Using the magic toolchains.xml

Maven has a toolchains.xml configuration mechanism, handy for specifying different JDKs for individual projects. This is an especially useful feature from Maven 2.0.9 onwards. Maven docs have got you covered on the setup.

Create aliases for quick switching

On Unix systems, you can configure aliases in your .bashrc or .zshrc file to quickly switch Java versions:

alias mvn11='JAVA_HOME=/usr/lib/jvm/java-11-oracle mvn'
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This command creates an alias mvn11 that runs Maven with Java 11. It's like having a fast travel point at your favorite tavern in an RPG!

Use modern Maven features

The <release> property in the compiler plugin, available from Java 9, is another way to tell Maven about the Java version:

<properties>
  <maven.compiler.release>11</maven.compiler.release>
</properties>
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No more time travel: Maven ensures you're using features available in that specific Java release.

Specific Scenarios: Maven & Java versions

Building with the previous JDK

Let's assume your project still uses Java 1.7 in a Java 1.8 landscape. You configure JDK 1.7 by setting:

<properties>
  <maven.compiler.source>1.7</maven.compiler.source>
  <maven.compiler.target>1.7</maven.compiler.target>
</properties>
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Verify the Java version used by Maven

To check which Java version Maven is using, fire this command:

mvn -version
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Look out for the Java version in the output. Hope it matches your expectations, unlike the final season of your favorite show.

Using .mavenrc for individual preferences

To set JAVA_HOME for a single user and not meddle with the system-wide settings, create a ~/.mavenrc file. It's like having your own personalized settings for the TV remote.

export JAVA_HOME=/opt/jdk/java-11-oracle
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Consistent builds with Maven Wrapper

For consistent build environments across developers and CI servers, commit a Maven wrapper (mvnw) into your source control. Now everybody is synchronised, just like a perfectly executed group dance routine.