黑马程序员10_动态代理

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原理图：

1、代理构架图：

2、动态代理的工作原理

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一、

通过Proxy的getProxyClass（）方法得到代理类的Class对象

通过Class对象反射出所有构造函数以及参数

然后通过Class对象反射出所有方法以及参数

import java.lang.reflect.Constructor;import java.lang.reflect.Method;import java.lang.reflect.Proxy;import java.util.Collection;public class Test2 {public static void main(String[] args) {Class proxyClass=Proxy.getProxyClass(Collection.class.getClassLoader(),Collection.class);//System.out.println(proxyClass.getName());//System.out.println(String.class.getName());System.out.println("-----------------构造函数--------------");/*$Proxy0(java.lang.reflect.InvocationHandler)*/Constructor[] constructors = proxyClass.getConstructors();for(Constructor constructor : constructors){String name = constructor.getName();StringBuilder sBuilder = new StringBuilder(name);sBuilder.append('(');Class[] clazzParams = constructor.getParameterTypes();for(Class clazzParam : clazzParams){sBuilder.append(clazzParam.getName()).append(',');}if(clazzParams!=null && clazzParams.length != 0)sBuilder.deleteCharAt(sBuilder.length()-1);sBuilder.append(')');System.out.println(sBuilder.toString());}System.out.println("-----------------方法（参数）--------------");Method[] methods = proxyClass.getMethods();for(Method method : methods){String name = method.getName();StringBuilder sBuilder = new StringBuilder(name);sBuilder.append('(');Class[] clazzParams = method.getParameterTypes();for(Class clazzParam : clazzParams){sBuilder.append(clazzParam.getName()).append(',');}if(clazzParams!=null && clazzParams.length != 0)sBuilder.deleteCharAt(sBuilder.length()-1);sBuilder.append(')');System.out.println(sBuilder.toString());}}}

二、

创建代理类的方式1：

通过Class对象反射出所有构造函数以及参数

编写一个最简单的InvocationHandler类

调用构造方法创建代理类

import java.lang.reflect.Constructor;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;import java.util.Collection;public class Test2 {public static void main(String[] args) throws Exception{Class proxyClass=Proxy.getProxyClass(Collection.class.getClassLoader(),Collection.class);Constructor constructor = proxyClass.getConstructor(InvocationHandler.class);class MyInvocationHander1 implements InvocationHandler{public Object invoke(Object proxy, Method method, Object[] args)throws Throwable {return null;}}Collection proxy1 = (Collection)constructor.newInstance(new MyInvocationHander1());System.out.println(proxy1);proxy1.clear();//clear()的返回类型是void，代理返回个null，不报错//proxy1.size();//size()返回类似是int，代理返回了个null，报空指针异常}}

创建代理类的方式2：

Proxy提供了一个方法 newProxyInstance( ClassLoader loader, Class<?>[]  interfaces, InvocationHandler h)

可以直接将类加载器的Class对象，需要实现的所有接口的Class对象的数组，还有InvocationHandler的实例对象 直接传进去，来创建代理类。

import java.lang.reflect.Constructor;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;import java.util.Collection;public class Test2 {public static void main(String[] args) throws Exception{//ClassLoader loader, Class<?>[] interfaces, InvocationHandler hCollection proxy=(Collection) Proxy.newProxyInstance(Collection.class.getClassLoader(),new Class[]{Collection.class}, new InvocationHandler() {@Overridepublic Object invoke(Object proxy, Method method, Object[] args)throws Throwable {return null;}});System.out.println(proxy);proxy.clear();//clear()的返回类型是void，代理返回个null，不报错//proxy.size();//size()返回类似是int，代理返回了个null，报空指针异常}}

三、

改写InvocationHandler的invoke方法，实现其真正代理功能

import java.lang.reflect.Constructor;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;import java.util.ArrayList;import java.util.Collection;public class Test2 {public static void main(String[] args) throws Exception{Collection proxy=(Collection) Proxy.newProxyInstance(Collection.class.getClassLoader(),new Class[]{Collection.class}, new InvocationHandler() {ArrayList arrayList=new ArrayList();@Overridepublic Object invoke(Object proxy, Method method, Object[] args)throws Throwable {System.out.println("InvocationHandler的             invoke()     被调用了");return method.invoke(arrayList, args);}});proxy.add("hello1");proxy.add("hello1");proxy.add("hello1");System.out.println(proxy.size());//size()返回类似是int，代理返回了个null，报空指针异常}}

注意：

调用代理对象的从Object类继承的hashCode()，equals()或toString()这几个方法是，代理对象将调用请求转发给Invocation对象，而其他的继承自Object的方法则调用代理类本身的方法

运行代码

import java.lang.reflect.Constructor;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;import java.util.ArrayList;import java.util.Collection;public class Test2 {public static void main(String[] args) throws Exception{Collection proxy=(Collection) Proxy.newProxyInstance(Collection.class.getClassLoader(),new Class[]{Collection.class}, new InvocationHandler() {ArrayList arrayList=new ArrayList();@Overridepublic Object invoke(Object proxy, Method method, Object[] args)throws Throwable {System.out.println("InvocationHandler的             invoke()     被调用了");return method.invoke(arrayList, args);}});System.out.println(proxy.toString());System.out.println(proxy.getClass().getName());}}

说明toString最终用到的是目标类的toString方法，而getClass是代理类自己的

四、创建灵活性更强的动态代理类

代码实现

import java.lang.reflect.Constructor;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;import java.util.ArrayList;import java.util.Collection;public class Test2 {public static void main(String[] args) throws Exception{Collection collection= (Collection) new MyProxyManger(new ArrayList(),new MyAdvice()).getProxy();collection.add("xiaozhi");collection.add("xiaozhi");collection.remove("xiaozhi");collection.size();}}class MyProxyManger{private Object target;private Advice advice;public MyProxyManger(Object target, Advice advice) {super();this.target = target;this.advice = advice;}public  Object getProxy() {return  Proxy.newProxyInstance(target.getClass().getClassLoader(),target.getClass().getInterfaces(), new InvocationHandler() {@Overridepublic Object invoke(Object proxy, Method method, Object[] args)throws Throwable {advice.beforeMehotd();System.out.println(method.getName());Object object=method.invoke(target, args);advice.afterMehotd();return object;}});}}

Advice

public interface Advice {public abstract void beforeMehotd();public abstract void afterMehotd();}

MyAdvice

public class MyAdvice implements Advice {@Overridepublic void beforeMehotd() {System.out.println("-----------------我是方法前调用的！-----------------");}@Overridepublic void afterMehotd() {System.out.println("-----------------我是方法后调用的！-----------------");}}

运行结果

五、实现AOP功能的封装与配置

工厂类BeanFactory负责创建目标类或代理类的实例对象，并通过配置文件实现切换。其getBean方法根据参数字符串返回一个相应的实例对象，如果参数字符串在配置文件中对应的类名不是ProxyFactoryBean，则直接返回该类的实例对象，否则，返回ProxyFactoryBean对象的getProxy方法返回的代理类。

AopFrameworkTest.java

package com.xiaozhi.proxy;import java.io.InputStream;import java.util.Collection;public class AopFrameworkTest {public static void main(String[] args) throws Exception {InputStream ips = AopFrameworkTest.class.getResourceAsStream("config.properties");Object bean = new BeanFactory(ips).getBean("xxx");System.out.println(bean.getClass().getName());((Collection)bean).clear();}}

config.properties

#xxx=java.util.ArrayListxxx=com.xiaozhi.proxy.ProxyFactoryBeanxxx.advice=com.xiaozhi.proxy.MyAdvicexxx.target=java.util.ArrayList

BeanFactory.java

package com.xiaozhi.proxy;import java.io.IOException;import java.io.InputStream;import java.util.Properties;public class BeanFactory {Properties props = new Properties();public BeanFactory(InputStream ips){try {props.load(ips);} catch (IOException e) {e.printStackTrace();}}public Object getBean(String name){String className = props.getProperty(name);Object bean = null;try {Class clazz = Class.forName(className);bean = clazz.newInstance();} catch (Exception e) {e.printStackTrace();} if(bean instanceof ProxyFactoryBean){Object proxy = null;ProxyFactoryBean proxyFactoryBean = (ProxyFactoryBean)bean;try {Advice advice = (Advice)Class.forName(props.getProperty(name + ".advice")).newInstance();Object target = Class.forName(props.getProperty(name + ".target")).newInstance();proxyFactoryBean.setAdvice(advice);proxyFactoryBean.setTarget(target);proxy = proxyFactoryBean.getProxy();} catch (Exception e) {e.printStackTrace();}return proxy;}return bean;}}

ProxyFactoryBean.java

package com.xiaozhi.proxy;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;public class ProxyFactoryBean {private Advice advice;private Object target;public Advice getAdvice() {return advice;}public void setAdvice(Advice advice) {this.advice = advice;}public Object getTarget() {return target;}public void setTarget(Object target) {this.target = target;}public  Object getProxy() {return  Proxy.newProxyInstance(target.getClass().getClassLoader(),target.getClass().getInterfaces(), new InvocationHandler() {@Overridepublic Object invoke(Object proxy, Method method, Object[] args)throws Throwable {advice.beforeMehotd();System.out.println(method.getName());Object object=method.invoke(target, args);advice.afterMehotd();return object;}});}}

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