How do I build a Maven Project with JDK 8?

Jenkins dropped official support for JDK 8 Maven builds. To still build projects using this Java version, you can either use our custom Maven plugin to select a JDK Toolchain based on your maven-compiler-plugin settings, or cross-compile with a newer JDK Version.

Toolchain Plugin

Our custom Maven Plugin can select a toolchain (e.g. JDK 8) during the build process. For this, the following workaround is required:

1. Set the JDK version to JDK 11.
2. Add the following maven goal to the command line:
   io.codemc.maven.plugins.toolchain:codemc-toolchain-selector:0.0.2-SNAPSHOT:select

Cross-Compiling

Cross-compiling is the process of targeting a different platform than the compiler itself.
In this case, it allows to use any JDK beyond Java 8 to generate a build that is still compatible with the older version.

You can achieve this by using source and target in the maven-compiler-plugin configuration. However, the usage of release is recommended in order to verify that you don't use any Java API methods introduced in later Java versions:

<plugins>
  <plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <version>3.10.1</version> <!-- Make sure to update when necessary -->
    <configuration>
      <release>8</release>
    </configuration>
  </plugin>
</plugins>