Java 动态代理实现AOP

JDK动态代理

JDK 1.3以后，Java提供了动态代理的技术，允许开发者在运行期创建接口的代理实例。在Sun刚推出动态代理时，还很难想象它有多大的实际用途，现在我们终于发现动态代理是实现AOP的绝好底层技术。

JDK的动态代理主要涉及到java.lang.reflect包中的两个类：Proxy和InvocationHandler。其中InvocationHandler是一个接口，可以通过实现该接口定义横切逻辑，并通过反射机制调用目标类的代码，动态将横切逻辑和业务逻辑编织在一起。

而Proxy利用InvocationHandler动态创建一个符合某一接口的实例，生成目标类的代理对象。这样讲一定很抽象，我们马上着手使用Proxy和InvocationHandler这两个魔法戒

public interface ForumService {
	public void removeTopic(int topicId);
	public void removeForum(int forrumId);
}

public class ForumServiceImpl implements ForumService {
	
	

	public void removeForum(int forumId) {
//		①-1开始对该方法进行性能监视 
//		PerformanceMonitor.begin("removeForum");
		 System.out.println("模拟删除Forum记录:"+forumId);
		try {
			Thread.currentThread().sleep(40);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
		
//		PerformanceMonitor.end();
		
	}

	public void removeTopic(int topicId) {
//		PerformanceMonitor.begin("removeTopic");
		System.out.println("模拟删除Topic记录:"+topicId);
		try {
			Thread.currentThread().sleep(20);
		} catch (InterruptedException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
//		PerformanceMonitor.end();
		
	}

}

public class PerformanceHandler implements InvocationHandler {
	
	private Object target;
	public PerformanceHandler(Object target) {
		this.target = target;
	}

	public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
		PerformanceMonitor.begin(target.getClass().getName()+"."+method.getName());
		Object obj = method.invoke(target, args);
		PerformanceMonitor.end();
		return obj;
	}
}

public class PerformanceMonitor {
//	①通过一个ThreadLocal保存调用线程相关的性能监视信息
	private static ThreadLocal<MethodPerformance> performanceRecord 
	= new ThreadLocal<MethodPerformance>();
	
//	②启动对某一目标方法的性能监视
	public static void begin(String method) {
		System.out.println("begin monitor...");
		MethodPerformance mp = new MethodPerformance(method);
		performanceRecord.set(mp);
	}
	
	public static void end() {
		System.out.println("end monitor...");
		MethodPerformance mp = performanceRecord.get();
		mp.printPerformance();
	}
}

public class MethodPerformance {
	
	private long begin;
	private long end;
	private String serviceMethod;
	
	public MethodPerformance(String serviceMethod) {
		this.serviceMethod = serviceMethod;
		this.begin = System.currentTimeMillis();
	}
	
	public void printPerformance() {
		end = System.currentTimeMillis();
		long elapse = begin - end;
		System.out.println(serviceMethod + " 花费 " + elapse + "毫秒");
	}
}

import java.lang.reflect.Proxy;
public class TestProxyForumService {

	public static void main(String[] args) {
		ForumService target = new ForumServiceImpl();
		
		PerformanceHandler handler = new PerformanceHandler(target);
		
		ForumService proxy = (ForumService)Proxy.newProxyInstance(
				target.getClass().getClassLoader(), 
				target.getClass().getInterfaces(), 
				handler);
		
		proxy.removeForum(10);
		proxy.removeTopic(234);
		
	}

}

输出结果：

begin monitor...
模拟删除Forum记录:10
end monitor...
test.aop.ForumServiceImpl.removeForum 花费 -40毫秒
begin monitor...
模拟删除Topic记录:234
end monitor...
test.aop.ForumServiceImpl.removeTopic 花费 -20毫秒

本文参考：http://www.iteye.com/topic/1123293