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Ajax technical composition and core principles explained
- 小云云Original
- 2018-01-12 16:19:251601browse
This article mainly introduces function throttling (throttle) and function debounce (debounce) of JavaScript performance optimization. Interested friends can refer to it. I hope it can help everyone.
1. Ajax
Features: Partial refresh, improve user experience, data is loaded from the server provider
2. The technical composition of AJax
is not a new technology, but the integration of previous technologies
Ajax: Asynchronous Javascript And Xml; (asynchronous JavaScript and XML)
Included technologies : JavaScript, XML, CSS, XMLHttpRequest
Asynchronous: After sending the request, it will be processed by the callback function without waiting for the result.
JavaScript: Send a request to the server, obtain the return result, and update the page
XML: Used to encapsulate data
##3. Ajax core principle
XMLHttpRequst object : Send a request to the server through this object. It is an asynchronous request technology, supported by all modern browsers (Chrome, IE5+)
1) Create XMLHttpReuest object
Non-IE browsers (Mozilla/Safari) ：var xhr=new XMLHttpRequest();IE:xhr=new ActiveXObject("Msxml2.XMLHTTP");
Lower version IE:xhr=new ActiveXObject("Microsfot.XMLHTTP");
2) Properties and methods of XMLHttpRequest object
a) Method: open("GET/POST", URL, true/false): used to establish a connection to the server There are three parameters:
Parameter 1: Submission method, post or get
Parameter 2: Requested URL
Parameter 3: Indicates synchronous or asynchronous request, true: indicates asynchronous request
false: Indicates synchronous request
send(data) :Send request
Parameters: Submitted content.
POST method: data is the submitted parameter, send(username=root&password=abc123);
GET method: send(null)
onreadystatechange: setting The callback function when the status changes. The callback function is used to obtain server data.
onreadystatechange=function(){
｝
Status code:
0: Not initialized 1: Loading
2: Loading completed
3: Request in progress
4: Request completed
responseXML: Data returned by the server (XML format)
Summary: Steps to use XMLHttpRequest:
1) Create XMLHttpRequest object
2) Set the request method and URL
xhr. open("GET/POST","url",true/false), true represents an asynchronous request, false represents a synchronous request
3) Set the callback function when the state changes
xhr.onreadystatechange=function(){}
0: Not initialized
1: Loading
2: Loading completed
3: Request in progress
4: Request completed
4) Send request
xhr.send( data),
If submitted for post, data is the submitted data. If submitted for get, the parameter can be null.
##
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>登录</title>
</head>
<body>
用户名：<input type="text" name="username" id="username"><br>
密码:<input type="password" name="password" id="password">
<a href="javascript:chkUser();">登录</a>
<p id="res"></p>
</body>
<script type="text/javascript">
var xhr;
/**
* 创建XMLHttpRequest对象
*/
function createXMLHttpRequest(){
//1、创建XMLHttpRequest对象
if(window.XMLHttpRequest){
//非IE内核浏览器
xhr=new XMLHttpRequest();
}else{
//IE浏览器
try{
xhr=new ActiveXObject("Msxml2.XMLHTTP");
}catch(e){
//IE低版本
xhr=new ActiveXObject("Microsoft.XMLHTTP");
}
}
}
/**
* 发送请求，用来检查用户名、密码是否正确
*/
function chkUser(){
//1、创建XMLHttpRequest
createXMLHttpRequest();
//2、获得用户名、密码
var username=document.getElementById("username").value;
var password=document.getElementById("password").value;
//3、与服务器建立连接：open
var url="login?username="+username+"&password="+password;
//方式1：get提交
//xhr.open("GET",url,true);
//方式2：post提交
var url2="login";
xhr.open("POST",url2,true);
//4、设置回调函数，获得服务器响应的数据
xhr.onreadystatechange=function(){
/*
readyState状态码：
0：未初始化
1：正在加载
2：加载完成
3：请求进行中
4：请求完成
*/
if(xhr.readyState==4){
//status,200表示响应正常
if(xhr.status==200){
//alert("从服务器返回的值为："+xhr.responseText);
var res=xhr.responseText;
if(res=='0'){
document.getElementById("res").innerHTML="登录成功";
}else{
document.getElementById("res").innerHTML="<font color='red'>登录失败</font>";
}
}else{
alert("出现在了异常:"+xhr.response.Text);
}
}
}
//5、发送请求
//方式1：get方式
//xhr.send(null);
//方式2:post方式：
//Post提交需要设置http请求头
xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
xhr.send("username="+username+"&password="+password);
}
</script>
</html>Server code:
package com.newer.login.web;
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 com.newer.login.bean.User;
import com.newer.login.service.UserService;
/**
* Servlet implementation class LoginServlet
*/
public class LoginServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
UserService userService = new UserService();
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
doPost(request,response);
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
// 1、获得页面参数
String username = request.getParameter("username");
String password = request.getParameter("password");
System.out.println("获得请求的参数username:"+username);
System.out.println("获得请求的参数password:"+password);
// 2、封装User对象
User user = new User();
user.setUsername(username);
user.setPassword(password);
// 3、调用服务类，完成用户名、密码的校验
User u = userService.login(user);
/*
* 传统方式 if(u!=null){ //表示登录成功 request.setAttribute("user", user);
* //跳转至首页... }else{ //登录失败，跳转登录页面
*
* }
*/
// ajax响应
PrintWriter out = response.getWriter();
if (u != null) {
//0成功，1失败
out.print(0);
}else{
out.print(1);
}
out.close();
}
}Related recommendations: One of php’s closest friends ajax technologyHow jquery implements ajax technology 3: $. get()Recommend 5 AJAX introductory tutorials to easily learn to use ajax technology
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