javaassist insert some code before method

gistfile1.java

package com.zavakid.javassist.test;
public class Hello {	
	public void say(){
		System.out.println("Hello world.");
	}
}

//======================

package com.zavakid.javassist.test;

import javassist.ClassPool;
import javassist.CtClass;
import javassist.CtMethod;

public class Test {
	public static void main(String[] args) throws Exception {
		ClassPool classPool = ClassPool.getDefault();
		CtClass clazz = classPool.get("com.zavakid.javassist.test.Hello");
		CtMethod method = clazz.getDeclaredMethod("say");
		method.insertBefore("{System.out.println(\"Hello.say()\");}");
		
		Hello newH = new Hello(); // this will load the original Hello.class
		newH.say();
		
		Class c = clazz.toClass();
		Hello h = (Hello) c.newInstance(); // this will throw LinkError
		h.say();				
	}
}