动态代理

//定义接口
public interface Foo
{
void doAction();
}
//实现一
public class FooImpl implements Foo
{
public FooImpl()
{
}

public void doAction()
{
System.out.println("in FooImp1.doAction()");
}
}
//实现二
public class FooImpl2 implements Foo
{
public FooImpl2()
{
}
public void doAction()
{
System.out.println("in FooImp2.doAction()");
}

}
//代理类
public class DynamicSubject implements InvocationHandler
{
private Object sub;

public DynamicSubject()
{
}

public DynamicSubject(Object obj)
{
sub = obj;
}

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable
{
System.out.println("before calling " + method);

method.invoke(sub, args);

System.out.println("after calling " + method);

return null;
}

}
//测试
public class Demo
{
public static void main(String[] args)
{

// 1.通用的动态代理实现

CommonInvocationHandler handler = new CommonInvocationHandler();

Foo f;

// 2.接口实现1

handler.setTarget(new FooImpl());

f = (Foo) Proxy.newProxyInstance(Foo.class.getClassLoader(),

new Class[] { Foo.class },

handler);

f.doAction();

// 3.接口实现2

handler.setTarget(new FooImpl2());

f = (Foo) Proxy.newProxyInstance(Foo.class.getClassLoader(),

new Class[] { Foo.class },

handler);

f.doAction();
}
}
----------->>也就是面向接口编程，完全可以写一个工厂类实现的，为什么要采用这个方式，如：

class Factory{
Foo fo ;
public Factory(Foo fo){
this.fo = fo;
}
public Foo getInstence(){
return fo;
}
}
然后创建Factory对象
=============》》 有什么差别么？？

import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class AopTest {

public static void main(String[] args) {

Before before = new Before() {
public void before() {
System.out.println("...before...");
}
};

After after = new After() {
public void after() {
System.out.println("...after...");
}
};

Hello hello = null;

// 普通方法执行
System.out.println("-------------普通执行-------------");
hello = new HelloEnglish();
hello.sayHello("bao110908");
hello.sayHi("bao110908");
System.out.println();

// 切入方法执行前（前置增强）
System.out.println("-------------前置增强-------------");
hello = HelloAopManager.getHelloProxy(new HelloEnglish(), before);
hello.sayHello("bao110908");
hello.sayHi("bao110908"); // sayHi 方法没有标注 @Enhancement 所以不会进行代码切入
System.out.println();

// 切入方法执行后（后置增强）
System.out.println("-------------后置增强-------------");
hello = HelloAopManager.getHelloProxy(new HelloEnglish(), after);
hello.sayHello("bao110908");
hello.sayHi("bao110908");
System.out.println();

// 切入方法执行前和执行后（环绕增强）
System.out.println("-------------环绕增强-------------");
hello = HelloAopManager.getHelloProxy(new HelloEnglish(), before, after);
hello.sayHello("bao110908");
hello.sayHi("bao110908");
System.out.println();
}
}



@Retention(RetentionPolicy.RUNTIME)
@interface Enhancement {
}

interface Hello {
@Enhancement
public void sayHello(String name);
public void sayHi(String name);
}

class HelloChinese implements Hello {
public void sayHello(String name) {
System.out.println(name + "，您好");
}
public void sayHi(String name) {
System.out.println("哈啰，" + name);
}
}

class HelloEnglish implements Hello {
public void sayHello(String name) {
System.out.println("Hello, " + name);
}
public void sayHi(String name) {
System.out.println("hi, " + name);
}
}

class HelloAopManager {
private HelloAopManager(){
}

public static Hello getHelloProxy(Hello hello, Before before) {
return getHelloProxy(hello, before, null);
}

public static Hello getHelloProxy(Hello hello, After after) {
return getHelloProxy(hello, null, after);
}

public static Hello getHelloProxy(Hello hello, Before before, After after) {
HelloHandler handler = new HelloHandler();
if(before != null) {
handler.setBefore(before);
}
if(after != null) {
handler.setAfter(after);
}
return handler.bind(hello);
}
}

/**
* 前置增强接口
*/
interface Before {
public void before();
}

/**
* 后置增强接口
*/
interface After {
public void after();
}

class HelloHandler implements InvocationHandler {

/**
* 需要进行代理的实例
*/
private Hello hello = null;

/**
* 前置增强
*/
private Before before = null;

/**
* 后置增强
*/
private After after = null;

/**
* InvocationHandler 接口的实现方法，进行动态代理
*/
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
// 看看接口中方法是否标注了需要 Enhancement
boolean b = method.isAnnotationPresent(Enhancement.class);
if(!b){
// 没有标注的话，按原方法执行
return method.invoke(hello, args);
}
// 有标注的话，进行方法的前置和后置增强
if(before != null) {
before.before();
}
Object obj = method.invoke(hello, args);
if(after != null) {
after.after();
}
return obj;
}

/**
* 将传入的 Hello 与 InvocationHandler 进行绑定，以获得代理类的实例
* @param hello
* @return
*/
public Hello bind(Hello hello) {
this.hello = hello;
Hello helloProxy = (Hello)Proxy.newProxyInstance(
hello.getClass().getClassLoader(),
hello.getClass().getInterfaces(),
this
);
return helloProxy;
}

public void setAfter(After after) {
this.after = after;
}

public void setBefore(Before before) {
this.before = before;
}
}