一.Struts2运行流程图：
二.运行流程分析：
1. 请求发送给StrutsPrepareAndExecuteFilter
2.StrutsPrepareAndExecuteFilter询问ActionMapper：该请求是否是一个Struts2请求（即是否返回一个非空的ActionMapping对象）
3. 若ActionMapper认为该请求是一个Struts2请求，则StrutsPrepareAndExecuteFilter把请求的处理交给ActionProxy
. ActionProxy通过ConfigurationManager 读取框架的配置文件，确定需要调用的Action类及Action方法
. ActionProxy创建一个ActionInvocation的实例，并进行初始化
6. ActionInvocation实例在调用Action的过程前后，涉及到相关拦截器（Intercepter）的调用。
7.Action执行完毕，ActionInvocation负责根据struts.xml中的配置找到对应的返回结果。调用Result的execute方法，渲染结果。在渲染的过程中可以使用Struts2框架中的标签。
8. 执行各个拦截器invocation.invoke()之后的代码
9. 把结果发送到客户端
三、相关API
•ActionMapping：Simpleclass that holds the action mapping information used to invoke a Struts action.The name and namespace arerequired
•ActionMapper：Whengiven anHttpServletRequest, theActionMapper
mayreturn null if no action invocation request matches, or it may return anActionMapping thatdescribes an action invocation for the framework totry
mayreturn null if no action invocation request matches, or it may return anActionMapping thatdescribes an action invocation for the framework totry
•ActionProxy：ActionProxy isan extra layer betweenXWork andthe
action so that different proxies are possible.
action so that different proxies are possible.
•ActionInvocation：AnActionInvocation represents the execution state of an Action. It holds the
Interceptors and the Action instance. By repeated re-entrant execution of the invoke() method,initially by theActionProxy,then by the Interceptors, the Interceptors are all executed, and then
the Action and the Result.
Interceptors and the Action instance. By repeated re-entrant execution of the invoke() method,initially by theActionProxy,then by the Interceptors, the Interceptors are all executed, and then
the Action and the Result.