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2.Struts执行流程
2.1 web.xml中 StrutsPrepareAndExecuteFilter类

2.2 找到doFilter方法
体现出一种设计模式
解释了Struts2中 request 并不是HttpServletRequest
request = prepare.wrap（包装）Request(request);

***：ActionMapping mapping = prepare.findActionMapping(request, response, true);

findActionMapping方法：
public ActionMapping findActionMapping() {
//先看内存中有没有映射结果！
ActionMapping mapping = (ActionMapping) request.getAttribute(STRUTS_ACTION_MAPPING_KEY);

//没有，找到ActionMapper构建
if (mapping == null || forceLookup) {

mapping = dispatcher.getContainer().getInstance(ActionMapper.class).
}

return mapping;
}

2.3 上面代码已经保证mapping不是null
if (mapping == null) {

} else {
//code execute
execute.executeAction(request, response, mapping);
}

executeAction方法原型如下：
public void executeAction() throws ServletException {
dispatcher.serviceAction(request, response, mapping);
}

*serviceAction原型
public void serviceAction(）{

ActionProxy proxy = getContainer().getInstance(ActionProxyFactory.class).createActionProxy(
namespace, name, method, extraContext, true, false);

}

*：寻找ActionInvocation

if (mapping.getResult() != null) {
Result result = mapping.getResult();
result.execute(proxy.getInvocation()：返回值类型是ActionInvocation);
} else {
proxy.execute();
}

Struts2执行过程