用servlet验证密码2

 function createXMLHttpRequest() {
            var XMLHttpRequest1;
            if (window.XMLHttpRequest) {
              XMLHttpRequest_test = new XMLHttpRequest();
            } else if (window.ActiveXObject) {
              try {
                XMLHttpRequest_test = new ActiveXObject("Msxml2.XMLHTTP");
              } catch (e) {
                XMLHttpRequest_test = new ActiveXObject("Microsoft.XMLHTTP");
              }
            }
            return XMLHttpRequest_test;
          }

          function ajax() {
            var un=document.getElementById("username").value;
            var pw=document.getElementById("password").value;
            var XMLHttpRequest_test = createXMLHttpRequest();
            //指明相应页面
            var url = "LoginServlet";
            XMLHttpRequest_test.open("POST", url, true);
            //请求头，保证不乱码
            XMLHttpRequest_test.setRequestHeader("Content-Type",
                "application/x-www-form-urlencoded");
            //将两个参数传到servlet
            XMLHttpRequest_test.send("userName=" +un+ "&passWord=" + pw);

            //处理从servlet返回的结果
            XMLHttpRequest_test.onreadystatechange = function() {
              //这个4代表已经发送完毕之后
              if (XMLHttpRequest_test.readyState == 4) {
                //200代表正确收到了返回结果
                if (XMLHttpRequest_test.status == 200) {
                  //弹出返回结果
                  //alert(XMLHttpRequest_test.responseText);
                  var result=XMLHttpRequest_test.responseText;
                  if(result=="1"){
                      //登陆成功
                      alert("登陆成功!您好:"+un+"您的密码为:"+pw);

                  }else if(result=="2"){
                      //更换class
                    var hh = document.getElementById("hd");
                      hh.className="msg";
                      hh.innerText = "用户名或密码不能为空";

                  }else{
                      //更换class
                    var hh = document.getElementById("hd");
                      hh.className="msg";
                      hh.innerText = "用户名或密码错误";
                  }
                } else {
                  //如果不能正常接受结果，你肯定是断网，或者我的服务器关掉了。
                  alert("网络连接中断！");
                }
              }
            }
                return false;//阻止提交，也就是防止原页面刷新导致修改的界面一闪而过
          }

package com.swpu;

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.Statement;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Servlet implementation class LoginServlet
 */
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    private String User;
    private String Password;

    String sql=null;
    Connection conn=null;
    Statement stmt=null;
    ResultSet rs=null;

    boolean isLoing=false;

    /**
     * @see HttpServlet#HttpServlet()
     */
    public LoginServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.getWriter().append("Served at: ").append(request.getContextPath());
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.setContentType("text/html;charset=UTF-8");
        response.setCharacterEncoding("utf-8");
        PrintWriter out=response.getWriter();
        //获取参数
        User=request.getParameter("userName");
        Password=request.getParameter("passWord");

        //连接数据库检测用户名和密码
        try {
            //连接数据库
            DriverManager.registerDriver(new com.mysql.jdbc.Driver());
            conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/homework?useUnicode=true&characterEncoding=UTF-8","root","root");
            stmt=conn.createStatement();
            sql="select password from login_tb where user='"+User+"'";
            rs=stmt.executeQuery(sql);

            if(rs.next()) {
                //获取输入用户名的密码进行检验，若与输入的一致则isLogin置为true，反之置false
                String pw=rs.getString("password");
                if (pw.equals(Password)) {
                    isLoing=true;
                }else {
                    isLoing=false;
                }
            }else {
                //若未查询到用户的存在也置为false
                isLoing=false;
            }

        } catch (Exception e) {
            // TODO: handle exception
            e.printStackTrace();
        }finally {
            try {
                if(rs!=null)
                    rs.close();
                if(stmt!=null)
                    stmt.close();
                if(conn!=null)
                    conn.close();
            } catch (Exception e2) {
                // TODO: handle exception
                e2.printStackTrace();
            }
        }

        if(isLoing) {
            //这个字符串将会在js中被接收
            //1代表登录成功
            //2代表用户名或密码为空
            //3代表用户名或密码错误
            out.write("1");
        }else if(User==""||Password==""){
            out.write("2");
        }else {
            out.write("3");
        }
            out.close();
    }

}