struts2中控制器中if语句判断前端传来值总是结果失败问题

struts2的控制器的代码：

 package cn.web.action;

import com.opensymphony.xwork2.ActionSupport;

import cn.web.daoimp.UserDaoImp;
import cn.web.service.Users;

public class UserAction extends ActionSupport {
  private  String username;
  private  String password;

  public UserAction(){}

  public UserAction(String username,String password){

      this.username=username;
      this.password=password;
  }



  public String getUsername() {
        return username;
    }
    public void setUsername(String username) {
        this.username = username;
    }
    public String getPassword() {
        return password;
    }
    public void setPassword(String password) {
        this.password = password;
    }

    @Override
    public String execute() throws Exception{
        UserDaoImp userimp = new UserDaoImp();
//      User user=new User();
        Users u =new Users(1,username,password);
//      users.setId(1);
//      users.setUsername(username);
//      users.setPassword(password);

        System.out.println(username);
        System.out.println(password);
        if ("a".equals(username)&&"a".equals(password)){
             return "error";

            }
        else {
            return "success";
        }

    }


    /*
     * 有一段代码
     * 
     */




}

execute（）方法中的数据当用户名和密码都是a的时候应该跳转到error.jsp

但是无论输入什么值跳转的都是else语句中的success.jsp
这到底是怎么回事

http://blog.csdn.net/smcfy/article/details/5693407