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绪论

java中的代理分为静态代理和动态代理，静态代理使用于同一类型的群体的代理，而动态代理适用于不同群体之间的代理，静态代理在编译器就已经存在了，并且编译成class文件，在我看来代理可以用来增强功能。

静态代理

举个例子说明，一看就知道什么是静态代理了

package a.h;

public interface Person {
    void eat();
}
package a.h;

public class Adult implements Person{
    @Override
    public void eat() {
        System.out.println("吃西虹市炒鸡蛋");
    }
}
package a.h;

public class Baby implements Person{
    @Override
    public void eat() {
        System.out.println("吃辅食");
    }
}
package a.h;

public class StaticPersonProxy implements Person{
    private Person p;

    public StaticPersonProxy(Person p){
        this.p=p;
    }

    @Override
    public void eat() {
        System.out.println("把饭盛碗里");
        System.out.println("坐在凳子上");
        p.eat();
        System.out.println("洗碗");
    }
}
package a.h;

public class StaticPersonTest {
    public static void main(String[] args) {
        Person adult = new Adult();
        StaticPersonProxy adultProxy = new StaticPersonProxy(adult);
        adultProxy.eat();

        System.out.println("---------------------");

        Person baby =new Baby();
        StaticPersonProxy babyProxy = new StaticPersonProxy(baby);
        babyProxy.eat();

    }
}

运行结果：

把饭盛碗里
坐在凳子上
吃西虹市炒鸡蛋
洗碗
---------------------
把饭盛碗里
坐在凳子上
吃辅食
洗碗

上面的例子可以看出这个代理类只能代理Person群体，如果想代理佳通工具或者水果等需要在定义自己的代理类。

动态代理

package a.i;

public interface HouseInterface {
    void bed();
}
package a.i;

public class Home implements HouseInterface{
    public void bed(){
        System.out.println("家里的床");
    }
}

package a.i;

public interface TrafficInteface {
    void hardBed();
}
package a.i;

public class Train implements TrafficInteface{
    public void hardBed(){
        System.out.println("火车硬卧");
    }
}

package a.i;

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

public class DynProxy implements InvocationHandler {
    private Object o;

    public DynProxy(Object o){
        this.o=o;
    }
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("脱了鞋");
        System.out.print("躺在");
        method.invoke(o,args);
        System.out.println("--------------");
        return null;
    }
}
package a.i;

import java.lang.reflect.Field;
import java.lang.reflect.Proxy;
import java.util.Properties;

public class DynProxyTest {
    public static void main(String[] args) {
        try {
            generatedProxyFiles();


            HouseInterface house = new Home();
            DynProxy dynProxy = new DynProxy(house);
            HouseInterface h = (HouseInterface) Proxy.newProxyInstance(house.getClass().getClassLoader(), house.getClass().getInterfaces(), dynProxy);
            h.bed();

            TrafficInteface train = new Train();
            DynProxy trainHandler = new DynProxy(train);
            TrafficInteface trainProxy = (TrafficInteface) Proxy.newProxyInstance(train.getClass().getClassLoader(), train.getClass().getInterfaces(), trainHandler);
            trainProxy.hardBed();
        } catch (Exception e) {
            e.printStackTrace();
        }


    }

    public static void generatedProxyFiles() throws Exception {
        Field field = System.class.getDeclaredField("props");
        field.setAccessible(true);
        Properties props = (Properties) field.get(null);
        props.put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
    }
}

运行结果：

脱了鞋
躺在家里的床
--------------
脱了鞋
躺在火车硬卧
--------------

上面的例子我们可以看到动态代理不仅代理了HouseInterface还代理了TrafficInteface。

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package com.sun.proxy;

import a.i.HouseInterface;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;

public final class $Proxy0 extends Proxy implements HouseInterface {
    private static Method m1;
    private static Method m2;
    private static Method m3;
    private static Method m0;

    public $Proxy0(InvocationHandler var1) throws  {
        super(var1);
    }

    public final boolean equals(Object var1) throws  {
        try {
            return (Boolean)super.h.invoke(this, m1, new Object[]{var1});
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

    public final String toString() throws  {
        try {
            return (String)super.h.invoke(this, m2, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final void bed() throws  {
        try {
            super.h.invoke(this, m3, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    public final int hashCode() throws  {
        try {
            return (Integer)super.h.invoke(this, m0, (Object[])null);
        } catch (RuntimeException | Error var2) {
            throw var2;
        } catch (Throwable var3) {
            throw new UndeclaredThrowableException(var3);
        }
    }

    static {
        try {
            m1 = Class.forName("java.lang.Object").getMethod("equals", Class.forName("java.lang.Object"));
            m2 = Class.forName("java.lang.Object").getMethod("toString");
            m3 = Class.forName("a.i.HouseInterface").getMethod("bed");
            m0 = Class.forName("java.lang.Object").getMethod("hashCode");
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

在生成的代理类中我们可以看到暴露了4个方法，有三个是Object的方法，有一个是我们定义的方法。所以我们通过invoke可以调用这些方法。