Java - creating a subclass dynamically

Question

I\'d like to create a subclass programatically. I guess I have few options - Javassist, CGLib, BCEL, or ASM.

The use case is that one app\'s internals are class-oriented

Answer 1

It's quite easy with Javassist:

import javassist.CannotCompileException;
import javassist.ClassPool;
import javassist.CtClass;
import javassist.NotFoundException;

static Class createClass( String fullName )
        throws NotFoundException, CannotCompileException
{
    ClassPool pool = ClassPool.getDefault();

    // Create the class.
    CtClass subClass = pool.makeClass( fullName );
    final CtClass superClass = pool.get( DefinitionBasedMigrator.class.getName() );
    subClass.setSuperclass( superClass );
    subClass.setModifiers( Modifier.PUBLIC );

    // Add a constructor which will call super( ... );
    CtClass[] params = new CtClass[]{
        pool.get( MigratorDefinition.class.getName() ),
        pool.get( GlobalConfiguration.class.getName()) 
    };
    final CtConstructor ctor = CtNewConstructor.make( params, null, CtNewConstructor.PASS_PARAMS, null, null, subClass );
    subClass.addConstructor( ctor );

    return subClass.toClass();
}

Maven dependency:

    org.javassist
    javassist
    3.22.0-GA