java动态署理- 一

java动态代理- 一

java 动态代理深度学习,

一.相关类及其方法:

java.lang.reflect.Proxy,
Proxy 提供用于创建动态代理类和实例的静态方法.
newProxyInstance()
返回一个指定接口的代理类实例，该接口可以将方法调用指派到指定的调用处理程序
(详见api文档)

java.lang.reflect.InvocationHandler,
InvocationHandler 是代理实例的调用处理程序 实现的接口。
invoke()
在代理实例上处理方法调用并返回结果。在与方法关联的代理实例上调用方法时，将在调用处理程序上调用此方法。
(详见api文档)

二.源代码:

被代理对象的接口及实现类:
package com.ml.test;

public interface Manager {
public void modify();
}

package com.ml.test;

public class ManagerImpl implements Manager {

@Override
public void modify() {
?? System.out.println("*******modify()方法被调用");
}
}

业务代理类:
package com.ml.test;

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

public class BusinessHandler implements InvocationHandler {

private Object object = null;

public BusinessHandler(Object object) {
?? this.object = object;
}

@Override
public Object invoke(Object proxy, Method method, Object[] args)
??? throws Throwable {
?? System.out.println("do something before method");
?? Object ret = method.invoke(this.object, args);
?? System.out.println("do something after method");
?? return ret;

}
}

客户端类:
package com.ml.test;
import java.lang.reflect.Proxy;
public class Client {

public static void main(String[] args) {
?? // 元对象(被代理对象)
?? ManagerImpl managerImpl = new ManagerImpl();

?? // 业务代理类
?? BusinessHandler securityHandler = new BusinessHandler(managerImpl);

?? // 获得代理类($Proxy0 extends Proxy implements Manager)的实例.
?? Manager managerProxy = (Manager) Proxy.newProxyInstance(managerImpl
???? .getClass().getClassLoader(), managerImpl.getClass()
???? .getInterfaces(), securityHandler);

?? managerProxy.modify();
}
}

三.执行结果:
do something before method
*******modify()方法被调用
do something after method

四.机制分析:

Proxy.(ClassLoader loader, Class<?>[] interfaces, InvocationHandler h)做了以下几件事.
(1)根据参数loader和interfaces调用方法 getProxyClass(loader, interfaces)创建代理类$Proxy.
$Proxy0类实现了interfaces的接口,并继承了Proxy类.
(2)实例化$Proxy0并在构造方法中把BusinessHandler传过去,接着$Proxy0调用父类Proxy的构造器,为h赋值,如下:
class Proxy{
?? InvocationHandler h=null;
?? protected Proxy(InvocationHandler h) {
??? this.h = h;
?? }
?? ...
}



下面是本例的$Proxy0类的源码(好不容易才把它提出来):

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 Manager {

private static Method m1;
private static Method m0;
private static Method m3;
private static Method m2;

static {
?? try {
??? m1 = Class.forName("java.lang.Object").getMethod("equals",
????? new Class[] { Class.forName("java.lang.Object") });
??? m0 = Class.forName("java.lang.Object").getMethod("hashCode",
????? new Class[0]);
??? m3 = Class.forName("com.ml.test.Manager").getMethod("modify",
????? new Class[0]);
??? m2 = Class.forName("java.lang.Object").getMethod("toString",
????? new Class[0]);
?? } catch (NoSuchMethodException nosuchmethodexception) {
??? throw new NoSuchMethodError(nosuchmethodexception.getMessage());
?? } catch (ClassNotFoundException classnotfoundexception) {
??? throw new NoClassDefFoundError(classnotfoundexception.getMessage());
?? }
}

public $Proxy0(InvocationHandler invocationhandler) {
?? super(invocationhandler);
}

@Override
public final boolean equals(Object obj) {
?? try {
??? return ((Boolean) super.h.invoke(this, m1, new Object[] { obj }))
????? .booleanValue();
?? } catch (Throwable throwable) {
??? throw new UndeclaredThrowableException(throwable);
?? }
}

@Override
public final int hashCode() {
?? try {
??? return ((Integer) super.h.invoke(this, m0, null)).intValue();
?? } catch (Throwable throwable) {
??? throw new UndeclaredThrowableException(throwable);
?? }
}

public final void modify() {
?? try {
??? super.h.invoke(this, m3, null);
??? return;
?? } catch (Error e) {
?? } catch (Throwable throwable) {
??? throw new UndeclaredThrowableException(throwable);
?? }
}

@Override
public final String toString() {
?? try {
??? return (String) super.h.invoke(this, m2, null);
?? } catch (Throwable throwable) {
??? throw new UndeclaredThrowableException(throwable);
?? }
}
}

接着把得到的$Proxy0实例强制转换成Manager.
当执行managerProxy.modify()方法时,就调用了$Proxy0类中的modify()方法.
在modify方法中,调用父类Proxy中的h的invoke()方法.
即InvocationHandler.invoke();

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