java静态代理和动态代理

先看静态代理的代码：

package com.reflect;

public interface HelloWorld {
	public void sayHi();
}

package com.reflect;

public class HelloWorldImpl implements HelloWorld {

	@Override
	public void sayHi() {
		System.out.println("Hi");
	}

}

package com.reflect;

public class HelloWorldStaticProxy implements HelloWorld {
	private HelloWorld helloWorld;

	public HelloWorldStaticProxy(HelloWorld helloWorld) {
		this.helloWorld = helloWorld;
	}

	@Override
	public void sayHi() {
		helloWorld.sayHi();
	}

}

package com.reflect;

public interface Welcome {

	public void welcome();
}

package com.reflect;

public class WelcomeImpl implements Welcome {

	@Override
	public void welcome() {
		System.out.println("welcome");
	}

}

package com.reflect;

public class WelcomeStaticProxy implements Welcome {
	private Welcome welcome;

	public WelcomeStaticProxy(Welcome welcome) {
		this.welcome = welcome;
	}

	@Override
	public void welcome() {
		welcome.welcome();
	}

}

测试代码

package com.reflect;

import junit.framework.TestCase;

public class TestProxy extends TestCase {

	public void testStaticProxy() {
		HelloWorld helloWorld = new HelloWorldStaticProxy(new HelloWorldImpl());
		helloWorld.sayHi();

		Welcome welcomeProxy = new WelcomeStaticProxy(new WelcomeImpl());
		welcomeProxy.welcome();
	}

	public void testDynamicProxy() {
		HelloWorldInvocationHandler handler = new HelloWorldInvocationHandler();
		
		HelloWorld helloWorld = (HelloWorld) handler.bind(new HelloWorldImpl());
		helloWorld.sayHi();

		Welcome welcome = (Welcome) handler.bind(new WelcomeImpl());
		welcome.welcome();
	}
}

测试一下静态代理

运行testStaticProxy，输出：

Hi
welcome

看看代码，发现一个静态代理类对应一个接口，有多少个接口，就需要多少个静态代理类。

现在看动态代理的代码：

package com.reflect;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class HelloWorldInvocationHandler implements InvocationHandler {
	private Object target;

	public Object bind(Object target) {
		this.target = target;
		return Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(), this);
	}

	@Override
	public Object invoke(Object proxy, Method method, Object[] args)
			throws Throwable {
		return method.invoke(target, args);
	}

}

运行testDynamicProxy：

输出

Hi
welcome

看到代码，一个动态代理类，可以对应多个接口，因为参数是Object。这样，多个接口，只要一个代理类就行了。