description The requested resource (/struts2/hello.action) is not available.

能访问index.jsp文件，但是提交时却出现上述错误，都检查好几天了，都没有解决这个问题，希望各位大虾们能帮帮我这个菜鸟啊~~，感激不尽啊
源代码如下：
struts.xml
  <?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE struts PUBLIC
    "-//Apache Software Foundation//DTD Struts Configuration 2.0//EN"
    "http://struts.apache.org/dtds/struts-2.0.dtd">
<struts>
<package name="mldn" namespace="/" extends="struts-default">
       <action name="hello" class="org.lxh.struts2.demo.HelloAction">
           <result name="success">
              /hello.jsp
           </result>
           <result name="error">
             /error.jsp
           </result>
       </action>
</package>
</struts>
web.xml
<?xml version="1.0" encoding="UTF-8"?><web-app id="WebApp_ID" version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">    <filter>        <filter-name>struts2</filter-name>        <filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>    </filter>    <filter-mapping>        <filter-name>struts2</filter-name>        <url-pattern>/*</url-pattern>    </filter-mapping><welcome-file-list>
        <welcome-file>hello.jsp</welcome-file>
 </welcome-file-list></web-app>
helloworld.java
package org.lxh.struts2.demo;import com.opensymphony.xwork2.ActionSupport;public class HelloAction extends ActionSupport {
    private String msg="Hello World" ;
public String getMsg() {
return ActionSupport.SUCCESS ;
}
public void setMsg(String msg) {
System.out.println("**********************");
this.msg = msg;
}
@Override
public String execute() throws Exception {
if("mldnlxh".equalsIgnoreCase(this.msg)){
return ActionSupport.SUCCESS;
}else{
return ActionSupport.ERROR;
}
}
}
hello.jsp
<%@ page language="java" import="java.util.*" pageEncoding="GBK"%>
<%@ taglib prefix="s" uri="/struts-tags" %>
<html>
  <head>
    <title>My JSP 'hello.jsp' starting page</title>
  </head>
  <body>
     <s:property value="msg"/>
  </body>
</html>
index.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<html>
  <head>
    <title>My JSP 'index.jsp' starting page</title>
  </head>
  <body>
     <form action="hello.action" method="post">
            请输入内容：<input type="text" name="msg">
               <input type="submit" value="提交">
     </form>
  </body>
</html>
errors.jsp
<%@ page language="java" import="java.util.*" pageEncoding="ISO-8859-1"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    <base href="<%=basePath%>">
    
    <title>My JSP 'errors.jsp' starting page</title>
    
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="cache-control" content="no-cache">
<meta http-equiv="expires" content="0">    
<meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
<meta http-equiv="description" content="This is my page">
<!--
<link rel="stylesheet" type="text/css" href="styles.css">
-->  </head>
  
  <body>
    This is my JSP page. <br>
  </body>
</html>