Why does Groovy compiler apparently produce 1.5 version of Java?

Question

After some problems with differences between JSE versions, I'm trying to log the Java compiler version used to compile (it's Groovy 2.1.9, Grails 2.3.8, Java 1.7.0_60 in fact).

After some rummaging around, I've constructed this piece of code to read the leading bytes of the class - see /http://en.wikipedia.org/wiki/Java_class_file#General_layout

(change the path to the class to match the package name):

class CompilerVersionSupport {

  public static String getVersion() {
    String classAsPath = 'com/my/organisation/CompilerVersionSupport.class';
    InputStream stream = (new CompilerVersionSupport()).getClass().getClassLoader().getResourceAsStream(classAsPath);
    DataInputStream ins = new DataInputStream (stream)

    assert( ins.readUnsignedShort() == 0xcafe )    
    assert( ins.readUnsignedShort() == 0xbabe )
    int minor = ins.readUnsignedShort();
    int major = ins.readUnsignedShort();
    ins.close();
    int javaVersion = major - 44 
    return "1.$javaVersion"
    }     
}

Trouble is, it returns 1.5.

What could be going on?

• Charles

Answer 1

The default Groovy behaviour is not to compile the code with the same bytecode version as the JDK being used. 1.5 is the default for compatibility reasons, IMHO. If you want the compiler to output newer bytecode you need to set that explicitly.

For example if you're using Maven to compile the code, you can use the GMavenPlus plugin. See the description of the targetBytecode parameter.

If you're not using Maven you can use -Dgroovy.target.bytecode=1.7 or research the possibilities for your particular build tool