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設計模式-代理模式

時間：2021-07-27 17:38:48 阅读：0 評論：0 收藏：0 [點我收藏+]

標簽：love 系統代理類 oca 解決效率問題 instance byte

7、代理模式
代理模式是指爲其他對象提供一種代理，以控制對這個對象的訪問，屬于結構型模式。在某些情況下，一個對象不適合或者不能直接引用另一個對象，而代理對象可以在客戶端和目標對象之間起到中介的作用。
代理模式一般包含三種角色：
抽象主題角色(Subject):抽象主題類的主要職責是聲明真實主題與代理的共同接口方法，該類可以是接口也可以是抽象方法。
真实主题角色（RealSubject):该类也被称为被代理類，该类定义了代理所表示的真实对象，是负责执行系統真正的业务逻辑对象。
代理主题角色Proxy：也被称为代理類，其内部有RealSubjuct的引用，因此具备完全的对RealSubject的代理权。客户端调用代理对象的方法，但是会在代理对象前后增加一些处理代码。

代理模式的通用寫法：

package com.jdwa.nomalproxy;

public interface ISubject {
    void request();
}

package com.jdwa.nomalproxy;

public class RealSubject implements ISubject{
    @Override
    public void request() {
        System.out.println("real service is called ");
    }
}

package com.jdwa.nomalproxy;

public class Proxy implements ISubject {

    private ISubject subject;

    public Proxy(ISubject subject){
        this.subject = subject;
    }


    @Override
    public void request() {
        before();
        subject.request();
        after();
    }

    private void before(){
        System.out.println("called before real service ...");
    }

    private void after(){
        System.out.println("called after real service ...");
    }

}

package com.jdwa.nomalproxy;

public class Client {
    public static void main(String[] args) {
        ISubject subject = new RealSubject();
        Proxy proxy = new Proxy(subject);
        proxy.request();
    }

}

從靜態代理帶動態代理：

package com.jdwa.staticproxy;

public interface IPerson {
    void findLove();
}

package com.jdwa.staticproxy;

public class Tom implements IPerson {
    @Override
    public void findLove() {
        System.out.println("must be a beautiful girl");
    }
}

package com.jdwa.staticproxy;

public class TomFather implements IPerson {

    private IPerson tom;

    public TomFather(IPerson tom){
        this.tom = tom;
    }
    @Override
    public void findLove() {
        before();
        tom.findLove();
        after();
    }

    private void before(){
        System.out.println("find a suitable girl ...");
    }

    private void after(){
        System.out.println("Get ready to be together ...");
    }
}

package com.jdwa.staticproxy;

public class Client {
    public static void main(String[] args) {
        IPerson tom = new Tom();
        IPerson tomFather = new TomFather(tom);
        tomFather.findLove();
    }
}

動態代理

package com.jdwa.staticproxy;

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

public class MatchMarker implements InvocationHandler {

    private IPerson target;

    public IPerson getInstance(IPerson target){
        this.target = target;
        Class<?> clazz = target.getClass();
        return (IPerson) Proxy.newProxyInstance(clazz.getClassLoader(),clazz.getInterfaces(),this);
    }

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

    private void before(){
        System.out.println("I‘m matchmarker,I hava already collect your infomation ,start to look for");
    }

    private void after(){
        System.out.println("They are very satisfied with each other");
    }
}

測試

package com.jdwa.staticproxy;

public class Client {
    public static void main(String[] args) {
//        IPerson tom = new Tom();
//        IPerson tomFather = new TomFather(tom);
//        tomFather.findLove();

        MatchMarker matchMarker = new MatchMarker();
        IPerson tom = matchMarker.getInstance(new Tom());
        tom.findLove();
    }
}

这就是JDK自带的動態代理实现。
我们都知道jdk動態代理采用字节重组，重新生成对象来代替原始对象，以达到動態代理的目的。jdk動態代理生成对象的步骤如下：
a、獲取被代理對象的引用，並獲取他的所有接口，反射獲取。
b、jdk動態代理類重新生成一个新的类，同时新的类要实现被代理類实现的所有接口
c、動態生成Java代碼新加的業務邏輯方法由一定的邏輯代碼調用
d、編譯新生成的Java代碼，得到class
e、重新加載到JVM中運行

我們通過將內存中的對象字節碼輸出，然後反編譯，可以查看代理對象的源代碼。

package com.jdwa.staticproxy;

import sun.misc.ProxyGenerator;

import java.io.FileOutputStream;

public class Client {
    public static void main(String[] args) throws Exception{
//        IPerson tom = new Tom();
//        IPerson tomFather = new TomFather(tom);
//        tomFather.findLove();

//        MatchMarker matchMarker = new MatchMarker();
//        IPerson tom = matchMarker.getInstance(new Tom());
//        tom.findLove();
        
        IPerson person = new MatchMarker().getInstance(new Tom());
        person.findLove();
        byte[] bytes = ProxyGenerator.generateProxyClass("$Proxy0",new Class[]{IPerson.class});
        FileOutputStream fos = new FileOutputStream("E://$Proxy0.class");
        fos.write(bytes);
        fos.close();
    }
}

通过源代码我们可以发现$Proxy0类继承了Proxy类，同时还实现了IPerson接口，重写了findLove方法。在静态块中用反射查找了目标对象的所有方法，而且保存了所有方法的引用，重写的方法用反射调用目标对象的方法。这些代码，都是jdk帮我们自动生成的。

CGLIB實現

package com.jdwa.staticproxy;


import org.springframework.cglib.proxy.Enhancer;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;

import java.lang.reflect.Method;

public class CGLibMatchMarker implements MethodInterceptor {

    public Object getInstance(Class<?> clazz) throws Exception{
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(clazz);
        enhancer.setCallback(this);

        return enhancer.create();
    }

    @Override
    public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
        before();
        Object obj = methodProxy.invokeSuper(o,objects);
        after();
        return obj;
    }

    private void before(){
        System.out.println("cglib ----I‘m matchmarker,I hava already collect your infomation ,start to look for");
    }

    private void after(){
        System.out.println("cglib ----They are very satisfied with each other");
    }
}

package com.jdwa.staticproxy;

import sun.misc.ProxyGenerator;

import java.io.FileOutputStream;

public class Client {
    public static void main(String[] args) throws Exception{
//        IPerson tom = new Tom();
//        IPerson tomFather = new TomFather(tom);
//        tomFather.findLove();

//        MatchMarker matchMarker = new MatchMarker();
//        IPerson tom = matchMarker.getInstance(new Tom());
//        tom.findLove();

//        IPerson person = new MatchMarker().getInstance(new Tom());
//        person.findLove();
//        byte[] bytes = ProxyGenerator.generateProxyClass("$Proxy0",new Class[]{IPerson.class});
//        FileOutputStream fos = new FileOutputStream("E://$Proxy0.class");
//        fos.write(bytes);
//        fos.close();

        Tom tom = (Tom) new CGLibMatchMarker().getInstance(Tom.class);
        tom.findLove();

    }
}

cglib的执行效率要高于jdk的，就是因为CGLib采用了FastClass机制，他的原理简单来说就是：为代理類和被代理類各生成一个类，这个类会为代理類和被代理類的方法分配一个INDEX（int类型）；这个INDEX当作一个入参，FastClass就可以直接定位要调用的方法并直接进行调用，省去了反射调用，所以调用效率比JDK代理通过反射调用高。

欢迎大家留言，以便于后面的人更快解決問題！另外亦欢迎大家可以关注我的微信公众号，方便利用零碎时间互相交流。共勉！

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設計模式-代理模式

標簽：love 系統代理類 oca 解決效率問題 instance byte

原文地址：https://www.cnblogs.com/caozz/p/proxy.html

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