原生的ajax
<%@ 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 'ajax.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">
-->
</head>
<body>
<input type="text" name="userName" onblur="validate();"><div></div>
<script type="text/javascript" src="js/jquery-1.12.4.js"></script>
<script type="text/javascript">
//输入框失去焦点 触发的事件
function validate(){
//获取用户的输入
var $name=$("[name='userName']").val();
//非空验证
if($name==null || $name==""){
$("[name='userName']").next().html("<span style='color:red'>用户名不能为空！！！</span>");
}else{
//1.创建XMLHttpReauest创建对象
var xhr=createXMLHttpReauest();
//2.设置回调回调函数 没有返回值
xhr.onreadystatechange=callBack;
//3.初始化参数组件
//xhr.open("GET","LoginServlet?name="+$name,true);
xhr.open("POST","LoginServlet",true);
var data="name="+$name;
//4.设置
xhr.setRequestHeader("Content-type","application/x-www-form-urlencoded");
xhr.send(data);
function callBack(){
if(xhr.readyState==4 && xhr.status==200){
var flag=xhr.responseText;
if(flag=="true"){
$("[name='userName']").next().html("<span style='color:red'>用户名已存在！！！</span>");
}else{
$("[name='userName']").next().html("<span style='color:green'>用户名可以使用！！！</span>");
}
}else{
}
}
}
}
function createXMLHttpReauest(){
if(window.XMLHttpRequest){//高版本的浏览器
return new XMLHttpRequest();
}else{//低版本浏览器
return new activeXObject("Microsoft.XMLHTTP");
}
}
</script>
</body>
</html>
package cn.bdqn.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet("/LoginServlet")
public class LoginServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
// TODO Auto-generated method stub
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
String name = req.getParameter("name");
boolean flag = false;
if ("admin".equals(name)) {
flag = true;
}
writer.print(flag);
writer.flush();
writer.close();
}
public static void main(String[] args) {
int a = 128;
int b = 128;
System.out.println(a == b);//true
Integer a1 = 127;
Integer a2 = 127;
Integer a3 = 128;
Integer a4 = 128;
System.out.println(a1 == a2);//true
System.out.println(a3 == a4);//false
Integer b1 = new Integer(127);
Integer b2 = new Integer(127);
System.out.println(b1 == b2);//false
Integer c1 = Integer.valueOf(127);
Integer c2 = Integer.valueOf(127);
System.out.println(c1 == c2);//true
}
}
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