如题,Java中动态代理有点迷惑,在网上看到的代码都是如下这类:
//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??
//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.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;
}
}
[color=#f0000]动态代理的主要作用就是:实现了日志和业务的分开,也就是某个类只是要提供了某些业务,比如银行取款业务。
这个类实现了取款业务的同时也需要实现日志功能,如果不用动态代理的话,那么由此一来该类代码里面已经额外地添加了自己不该添加的日志功能能代码。所以我们就得使用动态代理把它的业务代码和日志功能代码分开。所以用到了动态代理概念,spring里面的AOP就是一个很好的例子。[/color]希望对你 有帮助!!!
动态代理的主要作用就是:实现了日志和业务的分开,也就是某个类只是要提供了某些业务,比如银行取款业务。
这个类实现了取款业务的同时也需要实现日志功能,如果不用动态代理的话,那么由此一来该类代码里面已经额外地添加了自己不该添加的日志功能能代码。所以我们就得使用动态代理把它的业务代码和日志功能代码分开。所以用到了动态代理概念,spring里面的AOP就是一个很好的例子。 希望对你 有帮助!!!