First, Introduction
1, Ajax: The technique of exchanging data with the server and updating some Web pages without reloading the Web page, but it is not a new technology in itself
2, Core: XMLHttpRequest object. Ajax technology is mainly done through this object.
When creating this object, be sure to consider the browser's problem
Creation of XMLHttpRequest objects
XMLHttpRequest Object Properties
Where there are five types of readystate values
XMLHttpRequest Object Methods
3, simple example: use Ajax to complete the local refresh function: Local refresh, import content.html content in <span>
content.html Content
Flush.html
Xmlhttp.onreadystatechange=showmsgcallback: The Showmsgcallback () method is called when XmlHttp's request state changes, in fact, when the Xmlhttp.send () When the request is sent to the response, ReadyState will experience "2" (Request Processing), "3" (Request processed), "4" (response complete) three changes, and if the callback function is set before Xmlhttp.send (), it will call three times Showmsgcallback () Method. We do this when we set up readystate=4 because the response is complete and the server populates the response with the xmlhttp.response*** property
Clicking "Invoke Ajax Display" will dynamically generate "get data" in <span>
Second, Ajax asynchronous authentication: When the new user registration information, enter the ID, the asynchronous authentication ID is available
Login.html
Note how address rewriting is used here
Checkservlet
Packagecom.chen.ying;ImportJava.io.PrintWriter;Importjava.sql.Connection;ImportJava.sql.DriverManager;Importjava.sql.PreparedStatement;ImportJava.sql.ResultSet;ImportJavax.servlet.http.HttpServlet;Importjavax.servlet.http.HttpServletRequest;ImportJavax.servlet.http.HttpServletResponse; Public classCheckidextendsHttpServlet {FinalString dbdivre= "Com.mysql.jdbc.Driver"; FinalString url= "Jdbc:mysql://localhost:3306/test"; FinalString user= "Root"; FinalString password= "1995228"; Connection Conn=NULL; PreparedStatement pstmt=NULL; ResultSet RS=NULL; Public voiddoget (httpservletrequest req,httpservletresponse res) {intUserid=integer.parseint (Req.getparameter ("userid")); Try{System.out.println (userid); PrintWriter out=res.getwriter ();//the output stream that gets the responseClass.forName (Dbdivre); Conn=drivermanager.getconnection (Url,user,password); String SQL= "Select UserID from the person where userid=?"; Pstmt=conn.preparestatement (SQL); Pstmt.setint (1, UserID); RS=Pstmt.executequery (); if(Rs.next ()) {System.out.println ("Duplicate User ID"); Out.print ("True"); } Else{System.out.println ("ID Available"); Out.print ("False"); } }Catch(Exception e) {System.out.println (e); } } Public voiddoPost (httpservletrequest req,httpservletresponse res) { This. Doget (req, res); }}
Effect
When the user enters the ID, the cursor leaves the output box and, using AJAX technology, asynchronously verifies that the input ID is duplicated
Third, return XML data
1, requirements
14.javaweb Ajax Technical Details