java-ajax使用方法（异部请求）_什么叫异部请求-优快云博客

本文链接：https://blog.youkuaiyun.com/qq_36877577/article/details/64442587

本文展示了一个使用JSP技术实现的基本登录页面示例。该示例包括了使用JavaScript进行客户端验证的功能，确保用户输入非空，并通过Ajax检查用户名是否已被注册。此外，还介绍了如何配置JSP页面的基础设置。

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%
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 'index.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">
	-->
	
	<script type="text/javascript" src="<%=basePath + "/js/jquery-1.8.0.js"%>"></script>
	
	<script type="text/javascript">
		function checkLogin()
		{
			var username = $("#username").val();
			var pwd = $(".pwd").val();
			
			if(username == "" || pwd == "")
			{
				alert("用户名和密码不能为空!");
				return false;
			}
			
			return true;
		}
		
		function ajax()
		{
			//todo :发送异步请求，查询账户名是否存在
			var url = "<%=basePath + "login/doQuery.jsp"%>";			//请求地址
			
			//表单参数格式,{p1:"v1", p2:"v2"};
			//$.post(url, params, function(data){});
			$.post(url, {name:$("#username").val()}, 
				function(data)
				{
					if(data==1)
					{
						$("#msg").html("<font color='red'>已存在</font>");
					}
					else
					{
						$("#msg").html("可以注册");
					}
				}
			 );
			
		}
	</script>
	
  </head>
  
  <body>
  		<form action="<%=basePath + "/doLoginServlet"%>" method="post" onsubmit="return checkLogin()">
  			<table border="1">
  				<tr>
  					<td>用户名： </td>
					<td><input type="text" name="username" id="username" value="" onblur="ajax()"/>
					<span id="msg"></span>
					</td>
  				</tr>
  				<tr>
  					<td>密码： </td>
					<td><input type="password" name="pwd" class="pwd"/></td>
  				</tr>
  				
  				<tr>
  					<td colspan="2">
  						<input type="submit" value="登录"/>
  					 </td>
					
  				</tr>
  			</table>
  		
  		</form>
  </body>
</html>