java中反射讲解

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我是靠谱客的博主魁梧机器猫，最近开发中收集的这篇文章主要介绍java中反射讲解，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

1.问题描述：
在采用动态代理时，我采用接口接受变量
final T service = (T) Class.forName(implName).newInstance();

T proxy = (T)Proxy.newProxyInstance(service.getClass().getClassLoader(), new Class[]{clazz}, new InvocationHandler() {
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
Annotation ann = method.getAnnotation(Trans.class);
}
});

在上面Annotation ann = method.getAnnotation(Trans.class);会报错。原因method是其接口中的方法。
要想获取其实现类的方法对象 Method m = service.getClass().getMethod(method.getName,method.getParamterType());
这里获取的一定是实现类中的方法。

//动态代理
package cn.itcast.test;

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class DynamicProxyTest {
interface IHello {
void sayHello();
}

static class Hello implements IHello {

@Override
public void sayHello() {
System.out.println("hello word");

}

}

static class DynamicProxy implements InvocationHandler {
private Object target;

public void setTarget(Object target) {
this.target = target;
}

public Object getProxy(){
return Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(), this);
}

@Override
public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
// TODO Auto-generated method stub
System.out.println("nice");
return method.invoke(target, args);
}

}

public static void main(String[] args){
System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles","true");
DynamicProxy dynamicProxy = new DynamicProxy();
dynamicProxy.setTarget(new Hello());
IHello hello = (IHello)dynamicProxy.getProxy();
hello.sayHello();

}
}

反编译的结构是：
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;

final class $Proxy0 extends Proxy
implements DynamicProxyTest.IHello
{
private static Method m1;
private static Method m3;
private static Method m2;
private static Method m0;

static
{
try
{
m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
m3 = Class.forName("cn.itcast.test.DynamicProxyTest$IHello").getMethod("sayHello", new Class[0]);
m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
return;
}
catch (Exception localNoSuchMethodException)
{
throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
}

}

public $Proxy0(InvocationHandler paramInvocationHandler)
throws
{
super(paramInvocationHandler);
}

public final boolean equals(Object paramObject)
throws
{
try
{
return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue();
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}

public final void sayHello()
throws
{
try
{
this.h.invoke(this, m3, null);
return;
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}

public final String toString()
throws
{
try
{
return (String)this.h.invoke(this, m2, null);
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}

public final int hashCode()
throws
{
try
{
return ((Integer)this.h.invoke(this, m0, null)).intValue();
}
catch (Error|RuntimeException localError)
{
throw localError;
}
catch (Throwable localThrowable)
{
throw new UndeclaredThrowableException(localThrowable);
}
}

}