| Ajax登录案例，供大家参考，具体内容如下 
Msg package com.lbl.msg;public class Msg { String msg; int code; public Msg() { } public Msg(String msg, int code) { this.msg = msg; this.code = code; } public String getMsg() { return msg; } public void setMsg(String msg) { this.msg = msg; } public int getCode() { return code; } public void setCode(int code) { this.code = code; }}RegisterServlet package com.lbl.servlet;import com.fasterxml.jackson.databind.ObjectMapper;import com.lbl.msg.Msg;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 java.io.IOException;@WebServlet("/register")public class RegisterServlet extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //1:获取请求发送的数据 String username = request.getParameter("username"); response.setContentType("text/html;charset=UTF-8"); //2:判断用户名是否注册 if("abc123".equals(username)){ Msg msg = new Msg("用户名已经注册",0); //用户名已经注册 {"flag":false,"info":"用户名已经注册"};// String jsonStr = "{/"flag/":false,/"info/":/"用户名已经注册/"}"; //响应回浏览器 response.getWriter().write(new ObjectMapper().writeValueAsString(msg)); }else{ Msg msg = new Msg("可以注册",1); //用户名没有注册// String jsonStr = "{/"flag/":true,/"info/":/"可以注册/"}"; //响应回浏览器 response.getWriter().write(new ObjectMapper().writeValueAsString(msg)); } }}json_register.html <!DOCTYPE html><html lang="en"><head> <meta charset="UTF-8"> <title>Title</title> <script src="js/jquery-3.3.1.js"></script> <script type="application/javascript"> $(function () { //1: 给用户名输入框绑定失去焦点事件(onfocus onblur) $("#username").on("blur",function () { //获取用户名输入框数据 var username = $("#username").val(); //2:向服务器发出异步请求，让服务器去查询用户名是否存在 $.post( "register", //表示服务器的servlet路径 "username="+username, //表示向服务器发送的数据 function (data) { // msg:用户名已经注册 code:0 if(data.code==0){ // alert(data.info); $("#spanId").html(data.msg).css("color","green"); }else { $("#spanId").html(data.msg).css("color","red"); } }, "json" ); }); }); </script></head><body><div> <font>会员注册</font>USER REGISTER <form class="form-horizontal" style="margin-top: 5px;"> <table> <tr> <td>用户名</td> <td> <input type="text" id="username" name="username" placeholder="请输入用户名"> <span id="spanId"></span> </td> </tr> <tr> <td>密码</td> <td> <input type="password" placeholder="请输入密码"> </td> </tr> </table> <input type="submit" value="注册"/> </form></div></body></html>运行效果： 
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