Java Agent with BCEL

package com.agent.instrumentation;

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.lang.instrument.Instrumentation;
import java.security.ProtectionDomain;


import org.apache.bcel.classfile.*;



public class SimpleInstrumentation implements ClassFileTransformer {

    /** This is where the counts will be printed to **/
    @SuppressWarnings("unused")
    private static java.io.PrintStream output = System.err;


    public static void premain(String options, Instrumentation ins) {
        if (options != null)
            try {
                SimpleInstrumentation.output = new java.io.PrintStream(new java.io.FileOutputStream(options));
            }
            catch (java.io.FileNotFoundException e) {
                System.err.println(options + " - file not found");
            }

        ins.addTransformer(new SimpleInstrumentation());

        Class<?> classes[] = ins.getAllLoadedClasses();
        System.out.println("$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$");
        for (Class<?> c : classes)
            if (!c.getName().startsWith("java") && !c.getName().startsWith("sun") && !c.getName().startsWith("[Ljava"))
                System.out.println("CLASS LOADED: " + c.toString());
        System.out.println("$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$");
    }

    public byte[] transform(ClassLoader loader, String className,  Class<?> cBR, ProtectionDomain pD, byte[] classfileBuffer) throws IllegalClassFormatException {
        if (isSystemClass(className))
            return null;

        try {
            ClassParser cp = new ClassParser(new java.io.ByteArrayInputStream(classfileBuffer), className + ".java");
            JavaClass jc = cp.parse();
            Method methods[] = jc.getMethods();
            Field fields[] = jc.getFields();

            /*
             * Get all methods from the className
             */
            System.out.println("CLASS " + className + " has MATHODS:");
            for (Method m : methods)
                System.out.println("\t" + m.toString());
            /*
             * Get all attributes from the className
             */
            System.out.println("CLASS " + className + " has FIELDS:");
            for (Field f : fields)
                System.out.println("\t" + f.toString() + " ===> Current Value: " + f.getConstantValue());

            System.out.println("################################\n################################");
        }
        catch (Throwable exc) {
            System.err.println(exc);
        }

        return null;
    }

  /** Return true if this is a class we don't want to instrument **/
    private boolean isSystemClass(String className) {
        return ((className.startsWith("java/")) || (className.startsWith("javax/")) || (className.startsWith("sun/")));
    }





}