《Java编程思想》学习笔记6——Java动态代理

代理是一种常用的程序设计模式，如同网络代理一样，代理是介于调用者和真正调用目标对象之间的中间对象，代理在调用真正目标对象时提供一些额外或者不同的操作，真正的对目标对象的操作还是通过代理调用目标对象来完成。

简单的代理例子如下：

[java] view plaincopyprint?

//接口

interface Interface{
void doSomething();
void somethingElse(String arg);
}
//目标对象

class RealObject implement Interface{
public void doSomething(){
System.out.println(“RealObject doSomething”);
}
public void somethingElse(String arg){
System.out.println(“RealObject somethingElse ” + arg);
}
}
//简单代理对象

class SimpleProxy implements Interface(
private Interface proxied;
public SimpleProxy(Interface proxied){
this.proxied = proxied;
}
public void doSomething(){
System.out.println(“SimpleProxy doSomething”);
proxied.doSomething();
}
public void somethingElse(String arg){
System.out.println(“SimpleProxy somethingElse ” + arg);
proxied.somethingElse(arg);
}
)
Class SimpleProxyDemo{
public static void consumer(Interface iface){
iface.doSomething();
iface.somethingElse(“TestProxy”);
}
public static void main(String[] args){
//不是用代理

cosumer(new RealObject());
//使用代理

cosumer(new SimpleProxy(new RealObject()));
}
}

//接口
interface Interface{
void doSomething();
void somethingElse(String arg);
}
//目标对象
class RealObject implement Interface{
public void doSomething(){
System.out.println(“RealObject doSomething”);
}
public void somethingElse(String arg){
System.out.println(“RealObject somethingElse ” + arg);
}
}
//简单代理对象
class SimpleProxy implements Interface(
private Interface proxied;
public SimpleProxy(Interface proxied){
this.proxied = proxied;
}
public void doSomething(){
System.out.println(“SimpleProxy doSomething”);
proxied.doSomething();
}
public void somethingElse(String arg){
System.out.println(“SimpleProxy somethingElse ” + arg);
proxied.somethingElse(arg);
}
)
Class SimpleProxyDemo{
public static void consumer(Interface iface){
iface.doSomething();
iface.somethingElse(“TestProxy”);
}
public static void main(String[] args){
//不是用代理
cosumer(new RealObject());
//使用代理
cosumer(new SimpleProxy(new RealObject()));
}
}

输出结果为：

RealObject doSomething

RealObjectsomethingElse TestProxy

SimpleProxy doSomething

RealObject doSomething

SimpleProxy somethingElse TestProxy

RealObject somethingElse TestProxy

上面例子可以看出代理SimpleProxy在调用目标对象目标方法之前做了一些额外的操作。

Java中的代理是针对接口的动态代理，当然java也可以使用第三方的CGLIB实现针对类的代理，但是JDK中只支持针对接口的动态代理，我们只分析JDK的动态代理。

JDK动态代理的要素：

(1).实现了InvocationHandler的代理处理类，实现其invoke方法，该方法是代理调用目标对象方法以及提供额外操作的方法。

(2).使用Proxy.newProxyInstance(类加载器, 代理接口列表,InvocationHandler对象);方法创建实现了指定接口的动态代理。

JDK的代理例子如下：

[java] view plaincopyprint?

//接口

interface Interface{
void doSomething();
void somethingElse(String arg);
}
//目标对象

class RealObject implement Interface{
public void doSomething(){
System.out.println(“RealObject doSomething”);
}
public void somethingElse(String arg){
System.out.println(“RealObject somethingElse ” + arg);
}
}
//代理处理类

class DynamicProxyHandler implements InvocationHandler{
provate Object proxied;
public DynamicProxyHandler(Object proxied){
this.proxied = proxied;
}
//动态代理调用目标对象的方法

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable{
System.out.println(“Dynamic proxy invoke”);
return method.invoke(proxied, args);
}
}
class SimpleDynamicProxy{
public static void consumer(Interface iface){
iface.doSomething();
iface.somethingElse(“DynamicProxy”);
}
public static void main(String[] args){
RealObject real = new RealObject();
//不是用代理

consumer(real);
//创建动态代理

Interface proxy = (Interface) Proxy.newProxyInstance(
Interface.class.getClassLoader(),
new Class[]{Interface.class},
new DynamicProxyHandler(real)
);
cosumer(proxy);
}
}

//接口
interface Interface{
void doSomething();
void somethingElse(String arg);
}
//目标对象
class RealObject implement Interface{
public void doSomething(){
System.out.println(“RealObject doSomething”);
}
public void somethingElse(String arg){
System.out.println(“RealObject somethingElse ” + arg);
}
}
//代理处理类
class DynamicProxyHandler implements InvocationHandler{
provate Object proxied;
public DynamicProxyHandler(Object proxied){
this.proxied = proxied;
}
//动态代理调用目标对象的方法
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable{
System.out.println(“Dynamic proxy invoke”);
return method.invoke(proxied, args);
}
}
class SimpleDynamicProxy{
public static void consumer(Interface iface){
iface.doSomething();
iface.somethingElse(“DynamicProxy”);
}
public static void main(String[] args){
RealObject real = new RealObject();
//不是用代理
consumer(real);
//创建动态代理
Interface proxy = (Interface) Proxy.newProxyInstance(
Interface.class.getClassLoader(),
new Class[]{Interface.class},
new DynamicProxyHandler(real)
);
cosumer(proxy);
}
}

输出结果为：

RealObject doSomething

RealObject somethingElse DynamicProxy

Dynamic proxy invoke

RealObject doSomething

Dynamic proxyinvoke

RealObject somethingElse DynamicProxy