Compile Maven Module with Different Java Version

Question

My maven project has a few modules: server, web, etc.

I would like to build all but my server module on Java 6. For the server module, I\'d like to compile it with J

Answer 1

This is a very common question, so this answer is based on this article I wrote on my blog.

Maven Toolchains

To use multiple Java versions, you need to use Maven Toolchains, which require you to create a toolchains.xml file in your ~/.m2 Maven folder, containing all Java versions installed on your machine:

  
    jdk
    
      Java13
      13
    
    
      ${env.JAVA_HOME_13}
    
  
  
    jdk
    
      Java9
      9
    
    
      ${env.JAVA_HOME_9}
    
  
  
    jdk
    
      Java8
      8
    
    
      ${env.JAVA_HOME_8}
    
  
  
    jdk
    
      Java7
      7
    
    
      ${env.JAVA_HOME_7}
    
  
  
    jdk
    
      Java6
      6
    
    
      ${env.JAVA_HOME_6}
    
  

The JAVA_HOME_13, JAVA_HOME_9, JAVA_HOME_8, JAVA_HOME_7, JAVA_HOME_6 environment variables are configured so that they reference the path where the associated Java version is installed.

The FlexyPool parent pom.xml configuration file

The parent pom.xml Maven configuration file of the FlexyPool project defines the global Java version settings

    8
    ...

Now, we need to instruct both the compiler and the test plugins to use the configured java version.

    
        
            org.apache.maven.plugins
            maven-toolchains-plugin
            1.1
            
                
                    
                        toolchain
                    
                
            
            
                
                    
                        ${jdk.version}
                    
                
            
        

        
            org.apache.maven.plugins
            maven-compiler-plugin
            ${maven-compiler-plugin.version}
            
                ${jdk.version}
                ${jdk.version}
                true
                true
            
        

        
            org.apache.maven.plugins
            maven-surefire-plugin
            ${maven-surefire-plugin.version}
        
    

The FlexyPool child Maven module pom.xml using a different Java version

The flexy-pool-core-java9 child Maven module that requires a different Java version only needs to override the default jdk.version Maven property:

    9

And that's it, we can now build each module using its own minimum viable Java version.