jQuery异步请求大家都很熟悉，这里不再解释。直接上代码
jsp页面：
<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%> <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%> <% String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <base href="<%=basePath%>"> <title>My JSP 'ajax_form.jsp' starting page</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page"> <!-- <link rel="stylesheet" type="text/css" href="styles.css"> --> <!-- 引入jquery --> <script type="text/javascript" src="${pageContext.request.contextPath }/js/jquery-1.9.1.js"></script> <script type="text/javascript"> $(function(){ //alert($('#p').html());弹出具体的内容：hello }); function lost(){ //alert('失去焦点'); //alert($('#name')[0].value); 获取输入框的值，首先需要的到这个元素，这个元素是jquery对象，需要转为dom对象，使用数组下标的方法 $.ajax({ url: "FromServlet", type:"post", data:"name="+$('#name')[0].value+"&password=123",//向后台传送的数据格式 dataType:"json", success: function(data, textStatus){ //alert(data.password); //alert(data.name); //alert(textStatus); $("#td").after("<font color='red' fontsize='5'>"+data.name+"用户名已经存在！</font>"); }, error:function(XMLHttpRequest, textStatus, errorThrown){ alert(textStatus); } }); } </script> </head> <body> <p id="p">hello</p> <form action=""> <table> <tr> <td>用户名：</td> <td id="td"><input type="text" name="name" onblur="lost()" id="name"/></td> <tr> <td>密 码</td> <td><input type="password" name="password"/></td> </tr> <tr> <td><input type="submit" value="提交"/></td> <td><input type="reset" value="重置"/></td> </tr> </table> </form> </body> </html>
servlet后台代码;
package ajaxServlet; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import net.sf.json.JSONObject; public class FromServlet extends HttpServlet { /** * Constructor of the object. */ public FromServlet() { super(); } /** * Destruction of the servlet. <br> */ public void destroy() { super.destroy(); // Just puts "destroy" string in log // Put your code here } /** * The doGet method of the servlet. <br> * * This method is called when a form has its tag value method equals to get. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html"); PrintWriter out = response.getWriter(); } /** * The doPost method of the servlet. <br> * * This method is called when a form has its tag value method equals to post. * * @param request the request send by the client to the server * @param response the response send by the server to the client * @throws ServletException if an error occurred * @throws IOException if an error occurred */ public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //response.setContentType("text/html"); response.setCharacterEncoding("utf-8"); String name = request.getParameter("name"); String password = request.getParameter("password"); System.out.println("你输入的是="+name); System.out.println("你输入的密码是="+password); PrintWriter out = response.getWriter(); //String json = "{"success":"你好","type":"succ"}"; //out.println(json); //JSON对象 使用这种方法不用拼装json格式就可以自动转为json数据，不过要导入相应的jar文件，共六个 JSONObject jsonObject = new JSONObject(); jsonObject.accumulate("password", password).accumulate("name", name); response.setContentType("application/json"); response.getWriter().write(jsonObject.toString()); } /** * Initialization of the servlet. <br> * * @throws ServletException if an error occurs */ public void init() throws ServletException { // Put your code here } }