struts2 使用sitemesh web.xml配置ActionContextCleanUp的作用

 延长action中属性的生命周期，包括自定义属性，以便在jsp页面中进行访问，让actionContextcleanup过滤器来清除属性，不让action自己清除。

    为了使用WebWork,我们只需要在web.xml配置FilterDispatcher一个过滤器即可,阅读一下FilterDispatcher的JavaDoc和源码,我们可以看到它调用了:

 finally
 {
            ActionContextCleanUp.cleanUp(req);
 } 

在ActionContextCleanUp中,有这样的代码:

req.setAttribute(CLEANUP_PRESENT, Boolean.TRUE); 

如果FilterDispatcher检测到这个属性,就不会清除ActionContext中的内容了,而由ActionContextCleanUp后续的代码来清除,保证了一系列的Filter访问正确的ActionContext.

文档中提到,如果用到SiteMesh的Filter或者其他类似Filter,那么设置顺序是:

 ActionContextCleanUp filter
 SiteMesh filter
 FilterDispatcher
 所以最后我们的web.xml应该类似这样:

    <filter>
        <filter-name>ActionContextCleanUp</filter-name>
        <filter-class>com.opensymphony.webwork.dispatcher.ActionContextCleanUp</filter-class>
    </filter>

    <filter>
        <filter-name>sitemesh</filter-name>
        <filter-class>com.opensymphony.webwork.sitemesh.FreeMarkerPageFilter</filter-class>
    </filter>

    <filter>
        <filter-name>webwork</filter-name>
        <filter-class>com.opensymphony.webwork.dispatcher.FilterDispatcher</filter-class>
    </filter>

    <filter-mapping>
        <filter-name>ActionContextCleanUp</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

    <filter-mapping>
        <filter-name>sitemesh</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>

    <filter-mapping>
        <filter-name>webwork</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>