Java Proxy Design Pattern

IHello.java

package org.springsource.proxy;

/**
 * @author billzhang
 *
 */
public interface IHello {
	void sayHello(String name);
}

HelloImpl.java

package org.springsource.proxy;

/**
 * @author billzhang
 *
 */
public class HelloImpl implements IHello {

	public void sayHello(String name) {
		System.out.println("Hello "+name);
	}

}

Static Proxy:
StaticProxy.java

package org.springsource.proxy.stac;

import org.springsource.proxy.IHello;

/**
 * @author billzhang
 *
 */
public class StaticProxy implements IHello{
	private IHello hello;
	
	
	public StaticProxy(IHello hello) {
		super();
		this.hello = hello;
	}
	
	public void sayHello(String name){
		System.out.println("Start........");
		hello.sayHello(name);
		System.out.println("End..........");
	}
 
}

从上面我们看到代理对象的一个接口只服务于一种类型的对象，如果您要代理的方法很多，势必要为每个方法进行代理，static proxy 在程式规模稍大时就必定无法胜任。
Java在JDK 1.3之后加入协助开发Dynamic Proxy功能的类别，我们不必为特定对象与方法编写特定的代理，使用Dynamic Proxy，可以使得一个handler服务于各个对象，首先，一个handler必须实现 java.lang.reflect.InvocationHandler：

DynamicProxy.java

package org.springsource.proxy.dynamic;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
/**
 * @author billzhang
 *
 */
public class DynamicProxy implements InvocationHandler{
	
	private Object delegate;
	public Object bind(Object delegate) {
		this.delegate = delegate;
		return Proxy.newProxyInstance(delegate.getClass().getClassLoader(), delegate.getClass().getInterfaces(), this);
	}
	@Override
	public Object invoke(Object proxy, Method method, Object[] args)
			throws Throwable {
		Object result = null;
		try {
			System.out.println("Start "+method.getName()+"()");
			result = method.invoke(delegate, args);
			System.out.println("End "+method.getName()+"()");
		} catch (Exception e) {
			e.printStackTrace();
		}
		return result;
	}

}

package org.springsource.proxy.main;

import org.springsource.proxy.HelloImpl;
import org.springsource.proxy.IHello;
import org.springsource.proxy.dynamic.DynamicProxy;

/**
 * @author billzhang
 *
 */
public class Main {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		//static proxy
		/*IHello hello = new StaticProxy(new HelloImpl());
		hello.sayHello("Bill");*/
		
		//dynamic proxy
		DynamicProxy dp = new DynamicProxy();
		IHello hello = (IHello) dp.bind(new HelloImpl());
		hello.sayHello("Bill");
	}

}