compilation failure for spring boot application with java 9 and maven

Question

I am trying to build spring-boot application that uses java-9 and would be deployed to heroku. As a build tool I use maven

Answer 1

Rightly pointed out by @Robert you need to update your maven-compiler-plugin. To add to it, also as stated in the Maven/Jigsaw+9 over the maven plugins. The minimum compatible version of maven-compiler-plugin with current jdk-9+181 is 3.6.2 which can be used as :

    org.apache.maven.plugins
    maven-compiler-plugin
    3.6.2
    
        
            9
        
    

---

And to quote from one of the examples of maven-compiler-plugin with module-info.java here:

For projects that want to be compatible with older versions of Java (i.e 1.8 or below), but also want to provide a module-info.java for Java 9 projects must be aware that they need to call javac twice: the module-info.java must be compiled with release=9, while the rest of the sources must be compiled with a lower version of source/target.

which can be achieved using (JAVA_HOME set as 1.8.x) :

    org.apache.maven.plugins
    maven-compiler-plugin
    3.6.2
    
      
        default-compile
        
          
          
          
            9
          
          9
        
      
      
        base-compile
        
          compile
        
        
        
          
            module-info.java
          
        
      
    
    
    
      
      
        [1.5,9)
      
      1.5
      1.5
    

Few things to note there though are:

... you will need at least Maven 3.3.1 to specify a custom jdkToolchain in your plugin configuration

---

Or you can also configure the JAVA_HOME as /jdk9/Contents/Home/bin and use the following configuration:

    org.apache.maven.plugins
    maven-compiler-plugin
    3.6.2
    
      
        default-compile
        
          
          9
        
      
      
        base-compile
        
          compile
        
        
        
          
            module-info.java
          
        
      
    
    
    
      
      
        9
      
      6