jQuery常用的ajax-api-$.ajax()方法

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$.ajax({//这里是以键值对的形式，key的值不能乱写type : "POST",url  : "${pageContext.request.contextPath}/servlet/UserServlet",data : {"username":username},//必须是以json格式的数据success:function(backData){$("span").text(backData);}});

这里以检查注册用户名是否存在为例

jsp

<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html>  <head>    <title>检查注册用户名是否存在</title>  <script type="text/javascript" src="js/jquery-1.8.2.min.js"></script></head>  <body>  <!-- 在异步提交的方式下，form标签的action和method属性没有意义 -->  <form>  用户名:<input id="usernameID" type="text" name="username">  <input type="button" value="检查">  </form>  <span></span>  <script type="text/javascript">  $(":button").click(function(){  var username = $("#usernameID").val();$.ajax({//这里是以键值对的形式，key的值不能乱写type : "POST",url  : "${pageContext.request.contextPath}/servlet/UserServlet",data : {"username":username},//必须是以json格式的数据success:function(backData){$("span").text(backData);}});  });  </script>  </body></html>

servlet

public class UserServlet extends HttpServlet {public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {doPost(request, response);}public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {request.setCharacterEncoding("UTF-8");String username = request.getParameter("username");String tip = "";if("哈哈".equals(username)){tip = "已存在";}else{tip = "可用";}response.setContentType("text/html;charset=UTF-8");PrintWriter pw = response.getWriter();pw.write(tip);pw.flush();pw.close();}}

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