一个超级简单的struts，Action1中的转向为什么都是"success"呢？

index.jsp<%@ page language="java" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
    
    <title>My JSP 'index.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">  </head>
  
  <body>
    This is my JSP page. <br>
    <form action="yjr.do" method="post">
用户：<input type="text" name="username"><br>
<input type="submit" value="登录">
</form>
  </body>
</html>-----------------------
login_success.jsp<%@ page language="java" pageEncoding="ISO-8859-1"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
 
    <title>login_success.jsp</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">  </head>
  
  <body>
   <table width="80%" border="0">
      <tr>
        <td>Hello <%= request.getAttribute("username") %> !!</td>
      </tr>
    </table>
  </body>
</html>------------------------------
login_error.jsp
<%@ page language="java" pageEncoding="ISO-8859-1"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>  
    <title>login_error.jsp</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">

  </head>
  
  <body>
    error!!! <br>
  </body>
</html>-------------------------ActionForm1.java
import javax.servlet.http.HttpServletRequest;
import org.apache.struts.action.ActionErrors;
import org.apache.struts.action.ActionForm; 
import org.apache.struts.action.ActionMapping;public class ActionForm1 extends ActionForm{ 
private String username=null;public String getUsername() {
return username;
}public void setUsername(String username) {
this.username = username;
}
public void reset(ActionMapping mapping, HttpServletRequest request) {
  this.username = null;
}
}--------------------------------
Aciton1.java
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping; public class Action1 extends Action {
  public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response)
{

// if ("admin".equals(username) && "admin".equals(password)) {
// //转向到登录成功页面
// request.setAttribute("username", username);
// return mapping.findForward("success");
// }else {
// //转向到登录失败页面
// return mapping.findForward("error");
// }
    String target = new String("success");
ActionForm1 yy = (ActionForm1)form;
String username = yy.getUsername();
if ( username == null ) {
      target =new String("false");
    }
    else {
      request.setAttribute("username", username);
    }
return mapping.findForward(target);
}}
-------------------------
struts-config.xml
<?xml version="1.0" encoding="ISO-8859-1" ?><!DOCTYPE struts-config PUBLIC
          "-//Apache Software Foundation//DTD Struts Configuration 1.2//EN"
          "http://jakarta.apache.org/struts/dtds/struts-config_1_2.dtd"><!--
     This is a blank Struts configuration file with an example
     welcome action/page and other commented sample elements.     Tiles and the Struts Validator are configured using the factory defaults
     and are ready-to-use.     NOTE: If you have a generator tool to create the corresponding Java classes
     for you, you could include the details in the "form-bean" declarations.
     Otherwise, you would only define the "form-bean" element itself, with the
     corresponding "name" and "type" attributes, as shown here.
-->
<struts-config>    <form-beans>
      <form-bean name="ActionForm1" type="ActionForm1"/>
    </form-beans>    <action-mappings>
        <action
            path="/yjr"
            type="Action1"
            name="ActionForm1"
            scope="request"
            validate="false"
         >
         <forward name="success" path="/login_success.jsp"/>
         <forward name="false" path="/login_error.jsp"/>
    </action>
    </action-mappings>
    
</struts-config>
-----------------------------------
web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="2.4" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee   http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
  
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
  <servlet>
    <servlet-name>action</servlet-name>
    <servlet-class>org.apache.struts.action.ActionServlet</servlet-class>
    <init-param>
      <param-name>config</param-name>
      <param-value>/WEB-INF/struts-config.xml</param-value>
    </init-param>
    <init-param>
      <param-name>debug</param-name>
      <param-value>2</param-value>
    </init-param>
    <init-param>
      <param-name>detail</param-name>
      <param-value>2</param-value>
    </init-param>
    <load-on-startup>2</load-on-startup>
  </servlet>  <servlet-mapping>
    <servlet-name>action</servlet-name>
    <url-pattern>*.do</url-pattern>
  </servlet-mapping>
</web-app>
-----------------------------------我在文本框中什么也不输入 应该转向 "false" 的 login_error.jsp呀，
可是我文本框为null的时候还是转向了login_success.jsp!!!这是为什么啊，我是初学者，请大家帮我检查下哪儿出了问题？？