这篇博客讲了AOP代理-通知的3种方式：
1、MethodBeforeAdvice-前置通知
2、AfterReturningAdvice-正常返回后通知
3、MethodInterceptor-环绕通知
【框架】[Spring]纯Java的方式实现AOP切面(拦截)技术
现在本篇博客再详细讲解一下ThrowsAdvice-异常通知。
顾明思议，就是被代理的原型对象出异常了，就会运行到实现此接口中的一个方法。
这个和AfterReturningAdvice互补哦。
被代理的类：
package cn.hncu.javaImpl; public class Person { public void run(){ System.out.println("我在run..."); } public void run(int i){ System.out.println("我在run"+i+"..."); throw new IllegalArgumentException(); } public void say(){ System.out.println("我在say..."); } }
实现ThrowsAdvice的方法：
package cn.hncu.javaImpl; import org.springframework.aop.ThrowsAdvice; public class ThrowException implements ThrowsAdvice{ public void afterThrowing(Exception e) throws Throwable{ System.out.println("出异常了..."+e); } }
运行的方法：
@Test public void demo3(){ ProxyFactoryBean factory = new ProxyFactoryBean(); factory.setTarget(new Person());//给代理工厂一个原型对象 //切面 = 切点 + 通知 //切点 JdkRegexpMethodPointcut cut = new JdkRegexpMethodPointcut(); cut.setPatterns(new String[]{".*run.*",".*say.*"});//可以配置多个正则表达式 Advice throwsAdvice = new ThrowException(); //切面 = 切点 + 通知 Advisor throwsAdviceAdvisor = new DefaultPointcutAdvisor(cut, throwsAdvice); factory.addAdvisors(throwsAdviceAdvisor); Person p2 = (Person) factory.getObject();//从代理工厂中获取一个代理后的对象 p2.run(); p2.run(2222); }
运行结果:
有几个需要注意的地方：
1、就是原型对象的异常不能抓！一旦抓取就无法运行afterThrowing。
也就是只有出异常了，且没被抓，才会运行这个方法。
2、不能在运行的方法中直接new ThrowsAdvice然后实现afterThrowing方法，这样因为出异常，线程挂了，也会无法运行这个afterThrowing方法。
也就是不能在测试的方法中直接：
Advice throwsAdvice = new ThrowsAdvice() { public void afterThrowing(Exception e) throws Throwable{ System.out.println("出异常了..."+e); } };
这样也无法实现原型对象处异常拦截。
ThrowsAdvice源代码分析：
直接看ThrowsAdvice接口的源代码：
/* * Copyright 2002-2008 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.aop; /** * Tag interface for throws advice. * * <p>There are not any methods on this interface, as methods are invoked by * reflection. Implementing classes must implement methods of the form: * * <pre class="code">void afterThrowing([Method, args, target], ThrowableSubclass);</pre> * * <p>Some examples of valid methods would be: * * <pre class="code">public void afterThrowing(Exception ex)</pre> * <pre class="code">public void afterThrowing(RemoteException)</pre> * <pre class="code">public void afterThrowing(Method method, Object[] args, Object target, Exception ex)</pre> * <pre class="code">public void afterThrowing(Method method, Object[] args, Object target, ServletException ex)</pre> * * The first three arguments are optional, and only useful if we want further * information about the joinpoint, as in AspectJ <b>after-throwing</b> advice. * * <p><b>Note:</b> If a throws-advice method throws an exception itself, it will * override the original exception (i.e. change the exception thrown to the user). * The overriding exception will typically be a RuntimeException; this is compatible * with any method signature. However, if a throws-advice method throws a checked * exception, it will have to match the declared exceptions of the target method * and is hence to some degree coupled to specific target method signatures. * <b>Do not throw an undeclared checked exception that is incompatible with * the target method's signature!</b> * * @author Rod Johnson * @author Juergen Hoeller * @see AfterReturningAdvice * @see MethodBeforeAdvice */ public interface ThrowsAdvice extends AfterAdvice { }
你会发现里面并没有一个抽象方法！也行会有小伙伴迷茫，那为什么我们要实现那个方法啊。
没办法，因为我们是用Spring的框架，Spring内部用类反射来匹配了的，实现这个接口必须要实现这4个方法中的一个：
public void afterThrowing(Exception ex) public void afterThrowing(RemoteException) public void afterThrowing(Method method, Object[] args, Object target, Exception ex) public void afterThrowing(Method method, Object[] args, Object target, ServletException ex)
它的源代码有解释的，英文好一点就能看懂啦。
至于为什么不直接在这个接口中写这4个抽象类，可能怕代码太冗余吧。
毕竟，我们实现这个接口，我们用到的方法只会有一个，而如果都被声明成抽象方法了，那么，用户实现接口也必须实现这4个方法，显得冗余了。
所以估计Spring就干脆定义成标识接口了吧。
