java之动态代理

/**
 * 主题接口或者说目标类接口
 * @author zhu
 *
 */
public interface Subject {


void doSomething();

// void doOtherthing();
}

public class Target implements Subject {


@Override
public void doSomething() {
System.out.println("目标类方法");
}


}

public class Proxy implements Subject {
private Target target = new Target();


@Override
public void doSomething() {
System.out.println("系统功能：执行前！");
target.doSomething();
System.out.println("系统功能：执行后！");
}
}

public class Client {

public static void main(String[] args) {
Subject subject = new Proxy();
subject.doSomething();
}


}

 Class clazzProxy1 = Proxy.getProxyClass(Collection.class.getClassLoader(), Collection.class);// 第一步：获取Class字节码对象
                 Constructor constructor = clazzProxy1.getConstructor(InvocationHandler.class);// 第二步：通过Class得到构造器
                 class MyInvocationHander1 implements InvocationHandler{


        public Object invoke(Object proxy, Method method, Object[] args)
          throws Throwable {
          return null;
        }

}
Collection proxy = (Collection)constructor.newInstance(new MyInvocationHander1());// 第三步：获取Collection的代理类

final ArrayList target = new ArrayList();
Collection proxy = (Collection)Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(), new InvocationHandler(){


public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {
return null;
}

});

public interface Advice {
void beforeMethod(Method method);
void afterMethod(Method method);
}

public class MyAdvice implements Advice {
long beginTime = 0;
public void afterMethod(Method method) {
// TODO Auto-generated method stub
System.out.println("从传智播客毕业上班啦！");
long endTime = System.currentTimeMillis();
System.out.println(method.getName() + " running time of " + (endTime - beginTime));

}


public void beforeMethod(Method method) {
// TODO Auto-generated method stub
System.out.println("到传智播客来学习啦！");
beginTime = System.currentTimeMillis();
}


}

private static Object getProxy(final Object target,final Advice advice) {
Object proxy3 = Proxy.newProxyInstance(
target.getClass().getClassLoader(),
/*new Class[]{Collection.class},*/
target.getClass().getInterfaces(),
new InvocationHandler(){

public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {


/*long beginTime = System.currentTimeMillis();
Object retVal = method.invoke(target, args);
long endTime = System.currentTimeMillis();
System.out.println(method.getName() + " running time of " + (endTime - beginTime));
return retVal;*/



advice.beforeMethod(method);
Object retVal = method.invoke(target, args);
advice.afterMethod(method);
return retVal;

}
}
);
return proxy3;
}

  final ArrayList target = new ArrayList();
  Collection proxy = (Collection)getProxy(target,new MyAdvice());
  proxy.add("zxx");

xxx.advice=cn.itcast.MyAdvice

public class BeanFactory {
Properties props = new Properties();
public BeanFactory(InputStream ips){
try {
props.load(ips);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

public Object getBean(String name){
String className = props.getProperty(name);
Object bean = null;
try {
Class clazz = Class.forName(className);
bean = clazz.newInstance();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
} 
if(bean instanceof ProxyFactoryBean){
Object proxy = null;
ProxyFactoryBean proxyFactoryBean = (ProxyFactoryBean)bean;
try {
Advice advice = (Advice)Class.forName(props.getProperty(name + ".advice")).newInstance();
Object target = Class.forName(props.getProperty(name + ".target")).newInstance();
proxyFactoryBean.setAdvice(advice);
proxyFactoryBean.setTarget(target);
proxy = proxyFactoryBean.getProxy();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return proxy;
}
return bean;
}
}

public class ProxyFactoryBean {


private Advice advice;
private Object target;

public Advice getAdvice() {
return advice;
}


public void setAdvice(Advice advice) {
this.advice = advice;
}


public Object getTarget() {
return target;
}


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


public Object getProxy() {
// TODO Auto-generated method stub
Object proxy3 = Proxy.newProxyInstance(
target.getClass().getClassLoader(),
/*new Class[]{Collection.class},*/
target.getClass().getInterfaces(),
new InvocationHandler(){

public Object invoke(Object proxy, Method method, Object[] args)
throws Throwable {


/*long beginTime = System.currentTimeMillis();
Object retVal = method.invoke(target, args);
long endTime = System.currentTimeMillis();
System.out.println(method.getName() + " running time of " + (endTime - beginTime));
return retVal;*/



advice.beforeMethod(method);
Object retVal = method.invoke(target, args);
advice.afterMethod(method);
return retVal;

}
}
);
return proxy3;
}

}

public class AopFrameworkTest {// 通过配置文件获取目标对象和通告对象


/**
* 1、拿到配置文件
* 2、通过类名称得到类的实例对象
*/
public static void main(String[] args) throws Exception {
// TODO Auto-generated method stub
InputStream ips = AopFrameworkTest.class.getResourceAsStream("config.properties");
Object bean = new BeanFactory(ips).getBean("xxx");
System.out.println(bean.getClass().getName());
// ((Collection)bean).clear();

}
}

2、代理与jdbc

  动态代理一个典型应用就是实现数据库的连接池。由于使用JDBC的程序员习惯在使用完数据库的Connection对象后调用该对象的close方法关闭连接，这样连接池就失去作用了。这个问题我们可以使用动态代理技术来解决，当程序员调用Connection的close方法时，我们将其拦截下来，将其归还到连接池中，而不是直接关闭物理连接。

java之动态代理

原文：http://blog.csdn.net/u010213127/article/details/44835915