Struts2中EL表达式的取值范围问题

在Struts2中对request进行了装饰，增强了getAttribute()方法，改变了EL该方法的查找范围，具体为，查找request域，不存在，查找值栈，不存在，查找ContextMap，还是不存在，则返回null。

因为${对象名}，会使用findAttribute的查找，其顺序是page域->request域->session域->application域原理如下：

public class PageContext{//在page域中根据name获取valuepublic Object getAttribute(String name){return "找到了返回对象" | "没找到返回null";}//从四个域中逐个搜索，只要在其中一个找到，就不再继续寻找public Object findAttribute(String name){Object value = null;//搜page域value = this.getAttribute(name);if(value != null){return value;}//搜request域value = this.getRequest().getAttribute(name);if(value != null){return value;}//搜session域value = this.getSession().getAttribute(name);if(value != null){return value;}//搜application域value = this.getServletContext().getAttribute(name);if(value != null){return value;}return value;}
}

public class ServletConfigInterceptor extends AbstractInterceptor implements StrutsStatics {private static final long serialVersionUID = 605261777858676638L;public String intercept(ActionInvocation invocation) throws Exception {final Object action = invocation.getAction();final ActionContext context = invocation.getInvocationContext();if (action instanceof ServletRequestAware) {HttpServletRequest request = (HttpServletRequest) context.get(HTTP_REQUEST);((ServletRequestAware) action).setServletRequest(request);}if (action instanceof ServletResponseAware) {HttpServletResponse response = (HttpServletResponse) context.get(HTTP_RESPONSE);((ServletResponseAware) action).setServletResponse(response);}if (action instanceof ParameterAware) {((ParameterAware) action).setParameters((Map)context.getParameters());}if (action instanceof ApplicationAware) {((ApplicationAware) action).setApplication(context.getApplication());}if (action instanceof SessionAware) {((SessionAware) action).setSession(context.getSession());}if (action instanceof RequestAware) {((RequestAware) action).setRequest((Map) context.get("request"));}if (action instanceof PrincipalAware) {HttpServletRequest request = (HttpServletRequest) context.get(HTTP_REQUEST);if(request != null) {// We are in servtlet environment, so principal information resides in HttpServletRequest((PrincipalAware) action).setPrincipalProxy(new ServletPrincipalProxy(request));}}if (action instanceof ServletContextAware) {ServletContext servletContext = (ServletContext) context.get(SERVLET_CONTEXT);((ServletContextAware) action).setServletContext(servletContext);}return invocation.invoke();}
}