MyEclipse出现404错误

三个文件都配置好了，但一直出现404错误。按同样的方式配置其他文件能运行，就是不能运行这个配置，请高手指点一下。
web.xml为<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" 
xmlns="http://java.sun.com/xml/ns/javaee" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
    <filter>
        <filter-name>struts2</filter-name>
        <filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
    </filter>    <filter-mapping>
        <filter-name>struts2</filter-name>
        <url-pattern>/*</url-pattern>
    </filter-mapping>
</web-app>
struts2.xml为
<?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>
<!--  
    <constant name="struts.enable.DynamicMethodInvocation" value="false" />
    <constant name="struts.devMode" value="false" />    <include file="example.xml"/>    <package name="default" namespace="/" extends="struts-default">
        <default-action-ref name="index" />
        <action name="index">
            <result type="redirectAction">
                <param name="actionName">HelloWorld</param>
                <param name="namespace">/example</param>
            </result>
        </action>
    </package>
    -->    <!-- Add packages here -->
    <constant name="struts.devMode" value="true" />
        <package name="front" namespace="/" extends="struts-default">
   
        <action name="index" class="struts2.front.action.IndexAction3">
            <result>
            /ActionIntroduction.jsp
            </result>
        </action>
    </package></struts>
IndexAction.java为
package struts2.front.action;import com.opensymphony.xwork2.ActionSupport;public class IndexAction3 extends ActionSupport {


public String execute() {
return "success";
}
}