java中实现代理及委托代理模式
InvocationHandler 用于实现代理。
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如果不用InvocationHandler接口实现代理的话，我们写代码是这样的：
定义一个接口：
Java code
interface Greet
{
??? void sayHello(String name);
??? void goodBye();
}
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实现这个接口：
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Java code
class GreetImpl implements Greet
{
??? public void sayHello(String name)
??? {
??????? System.out.println("Hello " + name);
??? }
??? public void goodBye()
??? {
??????? System.out.println("Good bye.");
??? }
}
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实现一个代理类
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Java code
public class SimpleProxy implements Greet
{
??? private Greet greet = null;
??? SimpleProxy(Greet greet)
??? {
??????? this.greet = greet;
??? }
??? public void sayHello(String name)
??? {
??????? System.out.println("--before method sayHello");
??????? greet.sayHello(name);
??????? System.out.println("--after method sayHello");
??? }
??? public void goodBye()
??? {
??????? System.out.println("--before method goodBye");
??????? greet.goodBye();
??????? System.out.println("--after method goodBye");
??? }
??? /**
???? * @param args
???? */
??? public static void main(String[] args)
??? {??????? Greet tmp = new GreetImpl();??????? //生成代理
??????? Greet greet = new SimpleProxy(tmp);
???? greet.sayHello("walter");
??????? greet.goodBye();
??? }
}
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===============================================================================
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代理其实没什么的，再看看如果实现了InvocationHandler接口，
我们怎样实现代理。
还是要实现原来的Greet接口。
接口的实现还是GreetImpl。
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Java code
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
public class DebugProxy implements java.lang.reflect.InvocationHandler
{
??? private Object obj;
??? public static Object newInstance(Object obj)
??? {
??????? return java.lang.reflect.Proxy.newProxyInstance(obj.getClass().getClassLoader(),
??????????????? obj.getClass().getInterfaces(), new DebugProxy(obj));
??? }
??? private DebugProxy(Object obj)
??? {
??????? //Greet接口的：GreetImpl
??????? this.obj = obj;
??? }
???? //Method m：用的方法
?? //Object[] args：方法要入的???? //invoke实现对GreetImpl中方法的调用，同时也可以在这里加入自己想要实现的操作，??? //虽然调用原GreetImpl中的方法重要，但我想这里更看重的是通过自定义处理实现GreetImpl中没有的功能
??? public Object invoke(Object proxy, Method m, Object[] args) throws Throwable
??? {
??????? Object result;
??????? try
??????? {
??????????? //自定的理
??????????? System.out.println("--before method " + m.getName());
??????????? //用GreetImpl中方法
??????????? result = m.invoke(obj, args);
??????? }catch(InvocationTargetException e)
??????? {
??????????? throw e.getTargetException();
??????? }catch(Exception e)
??????? {
??????????? throw new RuntimeException("unexpected invocation exception: " + e.getMessage());
??????? }finally
??????? {
??????????? System.out.println("--after method " + m.getName());
??????? }
??????? return result;
??? }
??? /**
???? * @param args
???? */
??? public static void main(String[] args)
??? {
??????? Greet tmp = new GreetImpl();
???????
??????? Greet greet = (Greet) DebugProxy.newInstance(tmp);
?????????? //生成的greet和tmp有相同的hashCode
?????????? //通过DebugProxy构造的greet比原temp拥有更多功能
?????? greet.sayHello("walter");
?????????? greet.goodBye();
??? }
}