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java 代理的三种实现方式

时间:2016-03-14 18:33:08      阅读:237      评论:0      收藏:0      [点我收藏+]

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Java 代理模式有如下几种实现方式:

  1.静态代理。    

      2.JDK动态代理。

      3.CGLIB动态代理。

 

示例,有一个打招呼的接口。分别有两个实现,说hello,和握手。代码如下。

接口:

public interface Greeting {

    public void doGreet();
}

实现类:

public class SayHello implements Greeting {

    @Override
    public void doGreet() {
        System.out.println("Greeting by say ‘hello‘ .");
    }

}
public class ShakeHands implements Greeting {

    @Override
    public void doGreet() {
        System.out.println("Greeting by shake others‘s hands .");
    }

}
public class KissHello  {

    public void doGreet() {
        System.out.println("Greeting by kiss . ");
    }

}

 

在不改变代码的情况下,想在执行目标方法 前后 做一些其他操作。则可以通过代理方式来实现。

1.静态代理。需要创建代理类。代理类实现了和目标类一样的接口,代理类接收目标类对象,并在实现方法中调用目标类的实现方法前后做手脚。如下:

public class GreetStaticProxy implements Greeting {

    private Greeting hello;//被代理对象
    public GreetStaticProxy(Greeting hello){
        this.hello=hello;
    }
    
    @Override
    public void doGreet() {
        before();//执行其他操作
        this.hello.doGreet();//调用目标方法
        after();//执行其他操作
    }

    public void before(){
        System.out.println("[StaticProxy] Come to someone.");
    }
    public void after(){
        System.out.println("[StaticProxy] Back to his own corner");
    }
}

测试调用:

public class Main {

    public static void main(String[] args) {
        Greeting hello=new SayHello();
        Greeting shakeHands=new ShakeHands();
        
        //静态代理
        GreetStaticProxy staticHelloProxy=new GreetStaticProxy(hello);
        staticHelloProxy.doGreet();
        System.out.println();
        GreetStaticProxy shakeHandsProxy=new GreetStaticProxy(shakeHands);
        shakeHandsProxy.doGreet();
    }    
运行结果:
[StaticProxy] Come to someone. Greeting by say
‘hello‘ . [StaticProxy] Back to his own corner [StaticProxy] Come to someone. Greeting by shake others‘s hands . [StaticProxy] Back to his own corner

这个方式有弊端,如果有N个接口的实现类需要被代理,则需要创建N个代理类。

2.JDK动态代理

创建代理类,如下:

public class JdkProxy implements InvocationHandler {

    private Object target;
    
    public JdkProxy(Object obj){
        this.target=obj;
    }
    
    @Override
    public Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable {
        
        Object result=null;
        before();
        result=method.invoke(target, args);
        after();
        return result;
    }

    
    public void before(){
        System.out.println("[JdkProxy] Come to someone.");
    }
    public void after(){
        System.out.println("[JdkProxy] Back to his own corner");
    }
}

测试调用:

public class Main {

    public static void main(String[] args) {
        Greeting hello=new SayHello();
        Greeting shakeHands=new ShakeHands();
        
       
        //jdk动态代理
        JdkProxy dynamicProxy=new JdkProxy(hello);
        Greeting target=(Greeting) Proxy.newProxyInstance(hello.getClass().getClassLoader(),
                hello.getClass().getInterfaces(), dynamicProxy);
        target.doGreet();
        System.out.println();          
        
    }    
    
}

这种方式和第一种方式相比,虽然不需要创建很多代理类,

但是,他依赖与“被代理的对象需要实现接口” 即:在上面给出的代码示例中,动态代理可以代理SayHello和ShakeHands,却不能代理KissHello。因为KissHello没有实现接口。

3.CGLIB动态代理。

创建代理类:

public class CglibProxy implements MethodInterceptor {

    public static CglibProxy proxy=new CglibProxy();
    private CglibProxy(){}
    
    public static CglibProxy getInstance(){
        return proxy;
    }
    
    public <T> T getProxy(Class<T> cls){
        return (T) Enhancer.create(cls, this);
    }
    
    @Override
    public Object intercept(Object obj, Method method, Object[] arg,
            MethodProxy proxy) throws Throwable {
        Object result=null;
        try {
            before();
            result= proxy.invokeSuper(obj, arg);
            after();
        } catch (Exception e) {
            e.printStackTrace();
        }
        return result;
    }

    public void before(){
        System.out.println("[cglib] Come to someone.");
    }
    public void after(){
        System.out.println("[cglib] Back to his own corner.");
    }
}

调用示例:

public class Main {

    public static void main(String[] args) {
        
        //cglib代理
        Greeting targetProxy=CglibProxy.getInstance().getProxy(SayHello.class);
        targetProxy.doGreet();
        System.out.println();
        
        CglibProxy.getInstance().getInstance().getProxy(KissHello.class).doGreet();
        
               
    }    

}

 

综上,CGLIB动态代理最好,spring框架也用到了CGLIB包。

 

java 代理的三种实现方式

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原文地址:http://www.cnblogs.com/demingblog/p/5276475.html

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