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 blocke.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 blocke.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);}}