SSH项目中，jQuery AJAX响应速度超慢，SiteMesh filter惹的祸

解决方案：
    避免用不到SiteMesh的AJAX请求被SiteMesh拦截，具体如下
   （1）给Struts2配两个后缀，如.do,.ajax
    （2）SiteMesh中只拦截后缀为.do的请求
    （3）不用SiteMesh的AJAX action请求以.ajax结尾
--------------------------------
配置文件改动：
（1）struts.xml

    <constant name="struts.action.extension" value="do,ajax"></constant>

（2）web.xml

	<!-- SiteMesh -->
	<filter>
		<filter-name>sitemesh</filter-name>
		<filter-class>com.opensymphony.module.sitemesh.filter.PageFilter</filter-class>
	</filter>
	<filter-mapping>
		<filter-name>sitemesh</filter-name>
		<url-pattern>*.do</url-pattern>
	</filter-mapping>

	<!-- Struts2 -->
	<filter>
		<filter-name>struts2</filter-name>
		<filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
	</filter>

	<filter-mapping>
		<filter-name>struts2</filter-name>
		<url-pattern>*.do</url-pattern>
	</filter-mapping>

	<filter-mapping>
		<filter-name>struts2</filter-name>
		<url-pattern>*.ajax</url-pattern>
	</filter-mapping>