struts2.x dependency injection invalidity of

package com.loginCheck;
  
  import com.opensymphony.xwork2.ActionSupport;
  
  public class LoginAction extends ActionSupport {
  	private String userName=null;
  	private String userPassword=null;
  	
  	
  	@Override
  	public String execute(){
  		if(userName != null) {
  			if(userName.equals("wuyanxue")) {
  				
  				return SUCCESS;	
  			}
  		}
  		System.out.println(userName+" "+userPassword);
  		return ERROR;
  	}
  
  	public void setUserName(String userName) {
  		this.userName = userName;
  	}
  
  	public String getUserName() {
  		return userName;
  	}
  
  	public void setUserPassword(String userPassword) {
  		this.userPassword = userPassword;
  	}
  
  	public String getUserPassword() {
  		return userPassword;
  	}
  
  }

This is the Action class

----------------------------------------

This is a form jsp page







----------------------------------------


This is struts.xml configuration

<struts>
  	 
  	<constant name="struts.devMode" value="true" />
  	<constant name="struts.custom.i18n.resources" value="myResources"></constant>
  	
  	
  	<package name="example" namespace="" extends="struts-default">
  		<global-exception-mappings>
  			<exception-mapping result="Exception" exception="java.lang.Exception">
  			</exception-mapping>
  		</global-exception-mappings>
  		<action name="login" class="com.loginCheck.LoginAction">
              <interceptor-ref name="logger" />
              <interceptor-ref name="timer" />
          	<exception-mapping result="SQLException" exception="java.sql.SQLException"></exception-mapping>
              <result name="success">
              	/loginSuccess.jsp
              </result>
              <result name="error">
              	/loginFail.jsp
              </result>
          </action>
  	
      </package>
  
  </struts>

--------------------------

Problem Description: When I was in jsp page form, enter the account "wuyanxue" any password when console output null null

This shows struts2.x with jsp form values ​​are not instantiated LoginAction


exactly is the problem in any place where there is a problem with my code do ?


------ Solution ------------------------------------ --------
also need to add :

   <interceptor-ref name="defaultStack">  
                  <param name="exception.logEnabled">true</param>  
                  <param name="exception.logLevel">ERROR</param>  
              </interceptor-ref> 
  

http://www.iteye.com/problems/89992
------ For reference only --------------------- ------------------
seeking a big god help
------ For reference only ------------ ---------------------------
thanks for the answer