文档说明：（基于jquery-mysql的ajax请求用户名是否存在）​​​​​  新手上路——记录点滴​​
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项目目录：​​
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​jQuery-ajax-用户名异步请求_ajax​

wang.dbutil由高手封装的，借用​​
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整体项目，如链接过期，请关注留言，单独​​发送
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​链接：https://pan.baidu.com/s/1x0lDCoTrHvIuPdpYXel4fg

​密码：hlhm​

以下是jsp及servlet页面​​：
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<%@ page language="java" contentType="text/html; charset=utf-8"
  pageEncoding="utf-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Insert title here</title>
<script
  src="http://cdn.static.runoob.com/libs/jquery/1.10.2/jquery.min.js"></script>
<script type="text/javascript">
  $(function() {
    var name = $("#username").val();
    $("#username").blur(function() {
      //alert(name);
      $.ajax({
        type : "post",
        url : "/ajaxpro1/LoginServlet",

        data : {
          username : $("#username").val(),
        //username:name
        },
        success : function(result) {
          if(result=="true"){$("#spid").css("display","block")}
          if(result=="false"){$("#spid").css("display","none")}

        },
        error : function() {
          alert("请刷新页面 ：）");
        }
      });
    });
  });
</script>
</head>
<body>
  <form action="#">
    user:<input type="text" id=username name="username" value="" /><span id="spid">已存在</span>
     <input type="button" value="submit">
  </form>
  <style>
      #spid{
      display:none;
      text_color=red;
      }
  </style>
</body>
</html>
package wang.servlet;

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

import wang.service.LoginService;

/**
 * Servlet implementation class LoginServlet
 */
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @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());
        String name = request.getParameter("username");
        System.out.println(name+"loginServlet接收的数据！！！！！！");
        LoginService loginService = new LoginService();
        try {
            boolean exist = loginService.getUserName(name);
            System.out.println(exist+"servlet返回的数据");
            //request.getSession().setAttribute("exit", exist);
            
            //request.setAttribute("result", exist);
            //request.getRequestDispatcher("/login.jsp").forward(request, response);
            
            String exist1 = new Boolean(exist).toString();
            System.out.println(exist1+"String型！！！！！！！111");
            response.getWriter().write(exist1);
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }

}