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Relational Persistence for Java

There is a newer version: 3.6.0.Beta2

package org.hibernate.bytecode.javassist;

import javassist.ClassPool;
import javassist.NotFoundException;
import javassist.CtClass;
import javassist.CannotCompileException;
import org.hibernate.HibernateException;

import java.io.IOException;
import java.util.ArrayList;

/**
 * @author Steve Ebersole
 */
public class TransformingClassLoader extends ClassLoader {
	private ClassLoader parent;
	private ClassPool classPool;

	/*package*/ TransformingClassLoader(ClassLoader parent, String[] classpath) {
		this.parent = parent;
		classPool = new ClassPool( true );
		for ( int i = 0; i < classpath.length; i++ ) {
			try {
				classPool.appendClassPath( classpath[i] );
			}
			catch ( NotFoundException e ) {
				throw new HibernateException(
						"Unable to resolve requested classpath for transformation [" +
						classpath[i] + "] : " + e.getMessage()
				);
			}
		}
	}

	protected Class findClass(String name) throws ClassNotFoundException {
        try {
            CtClass cc = classPool.get( name );
	        // todo : modify the class definition if not already transformed...
            byte[] b = cc.toBytecode();
            return defineClass( name, b, 0, b.length );
        }
        catch ( NotFoundException e ) {
            throw new ClassNotFoundException();
        }
        catch ( IOException e ) {
            throw new ClassNotFoundException();
        }
        catch ( CannotCompileException e ) {
            throw new ClassNotFoundException();
        }
    }

	public void release() {
		classPool = null;
		parent = null;
	}
}