public interface HelloWorld {
    void sayHelloWorld() ;
}

public class HelloWorldImpl implements HelloWorld {
    @Override
    public void sayHelloWorld() {
        System.out.println("Hello World!");
    }
}

public class HelloWorldHandler implements InvocationHandler {
	// original object
	private Object oriObject;
	/**
	 * constructor 　　
	 * @param Object original　　
	 */
	public HelloWorldHandler(Object obj) {
		this.oriObject = obj;
	}
	public Object invoke(Object proxy, Method method, Object[] args)
			throws Throwable {
		Object result;
		// before invoke
		doBefore();
		// invoke original method
		result = method.invoke(this.oriObject, args);
		// after invoke
		doAfter();
		return result;
	}
	private void doBefore() {
		System.out.println("before method invoke");
	}
	private void doAfter() {
		System.out.println("after method invoke");
	}
	public static void main(String[] args) {

		HelloWorld hw = new HelloWorldImpl();
		InvocationHandler handler = new HelloWorldHandler(hw);
		HelloWorld proxy = (HelloWorld) Proxy.newProxyInstance(hw.getClass().getClassLoader(),hw.getClass().getInterfaces(),handler);
		proxy.sayHelloWorld();
	}
}