【框架】[Spring]纯Java方式实现AOP拦截-详解ThrowsAdvice异常通知

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本文源自【大学之旅_谙忆的博客】

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。

本文章由[谙忆]编写， 所有权利保留。

转载请注明出处：http://blog.csdn.net/qq_26525215

本文源自【大学之旅_谙忆的博客】