【问题中的配置】
spring相关配置文件root-context.xml mvc-context.xml其中mvc-context.xml被包含于root-context.xml
web.xml的配置为
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>
WEB-INF/spring/root-context.xml
</param-value>
</context-param>
<servlet>
<servlet-name>haha</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/spring/mvc-context.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>haha</servlet-name>
<url-pattern>/</url-pattern>
</servlet-mapping>
添加@Async的类被 <context:component-scan base-package="com.haha.service.impl"></context:component-scan>和
<context:component-scan base-package="com.haha.controller"></context:component-scan>放于mvc-context.xml
【修改后Ok的配置】
将 <context:component-scan base-package="com.haha.service.impl"></context:component-scan>放于root-context.xml
注意不能将controller的也迁移到root-context.xml，否则controller的Bean无法实例化
原因：详见解决要点
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解决要点：
一、In short, the context loaded by the ContextLoaderListener (generally from applicationContext.xml) is the parent of the context loaded by the DispatcherServlet (generally from *-servlet.xml). If you have the bean with the @Async method declared/component-scanned in both contexts, the version from the child context (DispatcherServlet) will override the one in the parent context (ContextLoaderListener). I verified this by excluding that component from component scanning in the *-servlet.xml -- it now works as expected.
要点：注意component-scan里面扫包不要重复扫。
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解决问题参考文献：
http://blog.csdn.net/haiyangzhishen/article/details/46930677
今天用了一下spring的@Async功能，遇到了一些问题。大家用的时候一定要注意：
1、异步方法和调用类不要在同一个类中
2、注解扫描时，要注意过滤，避免重复实例化，因为存在覆盖问题，@Async就失效了
非常感谢下面三篇文章的作者：
http://www.kaifajie.cn/XiangMuKuangJia/s13035.html
http://www.cnblogs.com/youngjoy/p/3817471.html
http://blog.csdn.net/jokes000/article/details/24649173