Struts2 中ActionContextCleanUp分析

 延長action中屬性的生命周期，包括自定義屬性，以便在jsp頁面中進行訪問，讓actionContextcleanup過濾器來清除屬性，不讓action自己清除。

    為了使用WebWork,我們只需要在web.xml配置FilterDispatcher一個過濾器即可,閱讀一下FilterDispatcher的JavaDoc和源碼,我們可以看到它調用了:

 finally
 {
            ActionContextCleanUp.cleanUp(req);
 } 

在ActionContextCleanUp中,有這樣的代碼:

req.setAttribute(CLEANUP_PRESENT, Boolean.TRUE); 

如果FilterDispatcher檢測到這個屬性,就不會清除ActionContext中的內容了,而由ActionContextCleanUp后續的代碼來清除,保證了一系列的Filter訪問正確的ActionContext.

文檔中提到,如果用到SiteMesh的Filter或者其他類似Filter,那么設置順序是:

 ActionContextCleanUp filter
 SiteMesh filter
 FilterDispatcher
 所以最后我們的web.xml應該類似這樣:

    <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>