A must-read analysis of Ajax technology components and core principles for beginners

This time I will bring you the analysis of Ajax technology composition and core principles that novices must read. What are the precautions that novices must read about Ajax technology composition and core principle analysis. The following is a practical case, let’s take a look together. take a look.

This article mainly analyzes the composition principles of Ajax technology for your reference. The specific content is as follows

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 technologiesAjax: Asynchronous
Javascript And ##Callback functionProcessing.
JavaScript: Send a request to the server, get the return result, and update the page
XML: Used to encapsulate data
3. Ajax core principle
XMLHttpRequst object: Use this object to send data to the server send request.

It is asynchronous request technology, all modern browsers support (Chrome, IE5+)

1) Create XMLHttpReuest object
Non-

IE browser

(Mozilla /Safari): var xhr=new XMLHttpRequest();IE:xhr=new ActiveXObject("Msxml2.XMLHTTP");Low 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)

b) Attribute:
onreadystatechange: Set when the state changes The callback function is used to obtain server data.
onreadystatechange=function(){　　　

｝

readyState: Server status response

Status code:

0: Not initialized

1: Loading
2: Loading completed 3: Request in progress 4: Request completed

responseText: Data returned by the server (text format)
responseXML: Data returned by the server (XML format)

Summary:

Steps to use XMLHttpRequest:

1) Create an XMLHttpRequest object 2) Set the request method and URL xhr.open("GET/POST ","url",true/false), true indicates an asynchronous request, false indicates a synchronous request
3) Set the callback function when the state changes
xhr.onreadystatechange=function(){}
0: Not Initialization
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 is null.

Judgement
User login
HTML page:

nbsp;html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">


<meta>
<title>登录</title>


  用户名：<input><br>
  密码:<input>
  <a>登录</a>
  <p></p>

<script>
  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==&#39;0&#39;){
           document.getElementById("res").innerHTML="登录成功";
         }else{
           document.getElementById("res").innerHTML="<font color=&#39;red&#39;>登录失败";
         }
         
        }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>

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();
  }
}

I believe you have mastered the method after reading the case in this article, more Please pay attention to other related articles on the php Chinese website!

Recommended reading:

Detailed explanation of the use of Ajax asynchronous loading

Use ajax to verify whether the registered user name exists

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