Java代理

Java proxy

這只是我研究java proxy寫的小例子，代碼不是那么規范，
代碼應該都能看懂不說明了，
一小例子

public class o {
	 public static void main(String[] args) throws Exception {
		 	face f= (face)Proxy.newProxyInstance(o.class.getClassLoader(), new Class[]{face.class}, new InvocationHandler() {
			
			face f=new imp();
			@Override
			public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
				// TODO Auto-generated method stub
				System.out.println("proxy------------------");

				Object o=method.invoke(f, args[0].toString());
				return o;
			}
		});
		System.out.println(f.a("dddd"));	 	
}

interface face{
	String a(String canshu);
}

class imp implements face{

	@Override
	public String a(String canshu) {
		// TODO Auto-generated method stub
		System.out.println(canshu);
		return "imp";
	}
	
}

接下來研究一下怎么查看生成的的類資訊，
進入Proxy.newProxyInstance（）方法，我們只用關心生成class的方法，其他的不用看，反正我看也看不懂，

        /*
         * Look up or generate the designated proxy class.
         */
        Class<?> cl = getProxyClass0(loader, intfs);

繼續進入呼叫了ProxyClassFactory的 public Class<?> apply(ClassLoader loader, Class<?>[] interfaces) 方法里面主要的是

		   //生成位元組資訊
		    byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
                proxyName, interfaces, accessFlags);
            try {
            	//這是根據位元組生成class實體
                return defineClass0(loader, proxyName,
                                    proxyClassFile, 0, proxyClassFile.length);
            } 

現在找到關鍵的代碼了我們自己調一下就行

		 public static void main(String[] args) throws Exception {
		
		 byte[] proxyClassFile = ProxyGenerator.generateProxyClass(
	                "com.example.demo.proxy1", new Class[]{face.class}, 1);//類路徑，class，1表示public
		 FileOutputStream fo=new FileOutputStream("C:\\Users\\Administrator.DESKTOP-3U5OF5D\\Desktop\\proxy1.class");
		 fo.write(proxyClassFile);
	 }

最后用反編譯工具看一下，我用的是idea自帶的

package com.example.demo;

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

public class proxy1 extends Proxy implements face {
    private static Method m1;
    private static Method m2;
    private static Method m3;
    private static Method m0;

    public proxy1(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 String a(String var1) throws  {
        try {
            return (String)super.h.invoke(this, m3, new Object[]{var1});
        } catch (RuntimeException | Error var3) {
            throw var3;
        } catch (Throwable var4) {
            throw new UndeclaredThrowableException(var4);
        }
    }

    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("com.example.demo.face").getMethod("a", Class.forName("java.lang.String"));
            m0 = Class.forName("java.lang.Object").getMethod("hashCode");
        } catch (NoSuchMethodException var2) {
            throw new NoSuchMethodError(var2.getMessage());
        } catch (ClassNotFoundException var3) {
            throw new NoClassDefFoundError(var3.getMessage());
        }
    }
}

看到生成的類繼承了proxy，所以說java代理是基于介面的因為java是單繼承，（還有一種cglib可以根據位元組碼增強），
生成的類也沒什么說的了，就是構造方法傳入一個我們自己的InvocationHandler，再定義Method屬性代表代理物件擁有的方法，然后呼叫invoke，