struts获取web页面时，request为null

struts获取web页面时，request为null。

错误信息如下：

java.lang.NullPointerException

    com.yy.action.loginAction1.execute(loginAction1.java:41)    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)    java.lang.reflect.Method.invoke(Method.java:606)

action代码如下：

loginAction1.Java

package com.yy.action;import java.util.Map;import org.apache.log4j.Logger;import com.opensymphony.xwork2.ActionContext;import com.opensymphony.xwork2.ActionSupport;public class loginAction1 extends ActionSupport{/* *  * */private static final long serialVersionUID = 1L;private static final Logger logger = Logger.getLogger("studyStruts2");private Map request;private Map session;private Map application;public loginAction1() {logger.info(new Throwable().getStackTrace()[0]);request = (Map)ActionContext.getContext().get("request");session = ActionContext.getContext().getSession();application = ActionContext.getContext().getApplication();}public String execute(){logger.info(new Throwable().getStackTrace()[0]);logger.info("a"+request);request.put("r1", "r2");application.put("a1", "a2");session.put("s1", "s2");return SUCCESS;}}

一直找不到原因。看马士兵讲的视频时，说是web.xml中struts过滤器原因。果不其然，2.0的配置会使得获取的request为null，而2.1的配置正常。

web.xml中struts配置如下（红色为正确配置）：<filter>
    <filter-name>struts2</filter-name>
<!--     <filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>  --> <!-- 2.0的配置会导致loginAction1中request为null  -->
<filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class> <!--2.1的配置正常运行 --> 
  </filter>
  <filter-mapping>
    <filter-name>struts2</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>