Ajax Simple User Registration verification

The core of Ajax is the XMLHttpRequest object
All modern browsers support XMLHttpRequest objects (IE5 and IE6 use ActiveXObject).
XMLHttpRequest is used to exchange data with the server in the background. This means that you can do this without reloading the entire Web page.
Update a section of the Web page.

Example: Simple verification of user name availability via asynchronous refresh of Ajax

Front-end JSP page code:

<%@ 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" >    function Cheackusername () {        var userName=document.getelementbyid ("UserName"). Value;

//Create XMLHttpRequest object:
var xmlhttp;
if (window.　　　　　　XMLHttpRequest)
{//compatible Ie7+,firefox,chrom,opera,safari
XMLHTTP = new XMLHttpRequest ();
　　　　　　}ELSE{//IE5,IE6
xmlhttp = new ActiveXObject ("Microsoft.XMLHTTP");
        Xmlhttp.onreadystatechange = function () {

if (xmlhttp.readystate==4&&xmlhttp.status==200) {                alert (xmlhttp.responsetext);                 = eval ("(" +xmlhttp.responsetext+ ")");                 if (dataobj.exist) {                    document.getElementById ("Tip"). innerhtml= "The user already exists! ";                } Else {                    document.getElementById ("Tip"). Innerhtml= "The user is available! ";                }            }        };

To send a request to the server:
Use the open () and send () methods of the XMLHttpRequest object

Xmlhttp.open ("Get", "Getinfo?action=cheackusername&username=" +username,true);    Xmlhttp.send (); }</script>

Create a servlet in the Tomcat server to impersonate the recipient and verify the user name:

The jar package required to introduce JSON: Commons-beanutils-1.7.0.jar Commons-lang-2.4.jar Json-lib-2.2.3-jdk15.jar

Commons-collections-3.2.jar Commons-logging-1.0.4.jar Ezmorph-1.0.3.jar

 PackageCom.cong.ajax;Importjava.io.IOException;ImportJava.io.PrintWriter;Importjavax.servlet.ServletException;ImportJavax.servlet.http.HttpServlet;Importjavax.servlet.http.HttpServletRequest;ImportJavax.servlet.http.HttpServletResponse;ImportNet.sf.json.JSONObject; Public classGetInfoextendsHttpServlet {Private Static Final LongSerialversionuid = 1L; protected voiddoget (httpservletrequest request, httpservletresponse response)throwsservletexception, IOException {doPost (request, response); }    protected voidDoPost (httpservletrequest request, httpservletresponse response)throwsservletexception, IOException {request.setcharacterencoding ("UTF-8"); Response.setcharacterencoding ("UTF-8"); Response.setcontenttype ("Text/html; Charset=utf-8 "); PrintWriter out=Response.getwriter (); String UserName=request.getparameter ("UserName"); Receive data from your browser jsonobject Resultjson=Newjsonobject ();//Create Jsonobject object, introduce necessary jar packageif("Hello". Equals (UserName)) {Resultjson.put ("Exist",true); }Else{resultjson.put ("Exist",false);        } out.println (Resultjson);        Out.flush ();    Out.close (); }}

To configure a servlet in Web. xml:

<servlet>      <Servlet-name>GetInfo</Servlet-name>      <Servlet-class>Com.cong.ajax.GetInfo</Servlet-class>  </servlet>    <servlet-mapping>      <Servlet-name>GetInfo</Servlet-name>      <Url-pattern>/getinfo</Url-pattern>  </servlet-mapping>

Ajax Simple User Registration verification