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

Posted 2022-12-16 谙忆

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】

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】