The use of traditional methods in Web pages to realize the specific interpretation of asynchronous verification

Learning JavaScript asynchronous checksum is often from the most traditional XMLHttpRequest, today Saturday. Let me talk a little bit about the traditional calibration:

Code 1--index.jsp File:

<%@ page language= "java" contenttype= "text/html; Charset=utf-8 "pageencoding=" UTF-8 "%><%string basepath = request.getscheme () +"://"+request.getservername () +" : "+request.getserverport () +request.getcontextpath () +"/";%><! DOCTYPE HTML PUBLIC "-//w3c//dtd HTML 4.01 transitional//en" >
Code 2--demo1.jsp File:
<%@ page language= "java" contenttype= "text/html; Charset=utf-8 "pageencoding=" UTF-8 "%><%string basepath = request.getscheme () +"://"+request.getservername () +" : "+request.getserverport () +request.getcontextpath () +"/";%><! DOCTYPE HTML PUBLIC "-//w3c//dtd HTML 4.01 transitional//en" >
");                var Responsevalue=xmlhttprequest.responsetext; if (responsevalue==1) {document.getElementById ("Showusername"). Innerhtml= "<font size=\" 2\ "color=\" red\ "&G  T Username has been used!            </font> "; }else if (responsevalue==2) {document.getElementById ("Showusername"). Innerhtml= "<font size=\" 2\ "color=\" Green\ "> Username effective!!
！
</font> "; }else{//failed document.getElementById ("Showusername") with servlet interaction. innerhtml= "<font size=\" 2\ "Colo R=\ "red\" > Request send failed.            </font> ";                      }            }           }; if (xmlhttprequest.readystate==0) {Xmlhttprequest.open ("get", "<%=basepath%>ajaxcheckusernameservlet?") Username= "+value,true);///Second step: completion of the request initialization. Make a request.
The three parameters in the Open method are: Request mode, path, asynchronous (true means async). false = Synchronous)}}}</script> 
</font> </center></body>
Code 3--demo2.jsp File:
<%@ page language= "java" contenttype= "text/html; Charset=utf-8 "pageencoding=" UTF-8 "%><%string basepath = request.getscheme () +"://"+request.getservername () +" : "+request.getserverport () +request.getcontextpath () +"/";%><! DOCTYPE HTML PUBLIC "-//w3c//dtd HTML 4.01 transitional//en" >
"); } if (xmlhttprequest.readystate==4) {//client Receive server-side information is complete. Fourth step: Handle the response information sent back by the server if (xmlhttprequest.status==200) {//Console.log successfully interacted with the servlet ("The client has fully received the server-side processing response.
");                var Responsevalue=xmlhttprequest.responsetext; if (responsevalue==1) {document.getElementById ("Showusername"). Innerhtml= "<font size=\" 2\ "color=\" red\ "&G  T Username has been used!            </font> "; }else if (responsevalue==2) {document.getElementById ("Showusername"). Innerhtml= "<font size=\" 2\ "color=\" Green\ "> Username effective!
！
。        </font> "; }else{//failed document.getElementById ("Showusername") with servlet interaction. innerhtml= "<font size=\" 2\ "Colo R=\ "red\" > Request send failed!
</font> ";                      }            }           }; if (xmlhttprequest.readystate==0) {Xmlhttprequest.open ("post", "<%=basepath%>ajaxcheckusernameservlet?") Username= "+value,true);///Second step: Complete request initialization, request.
The three parameters in the Open method are: Request mode, path, asynchronous (true means asynchronous, false = synchronous)}}}</script>
</font> </center></body>
Code 4--ajaxcheckusernameservlet.java File:
Package Com.ghj.packagofserlet;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;public Class Ajaxcheckusernameservlet extends HttpServlet {private static final long Serialversionuid = 6387744976765210524l;/** * Processing D  Asynchronous Validation in emo1.jsp * * @author Gaohuanjie */public void doget (HttpServletRequest request, httpservletresponse response) throws Servletexception, IOException {try{response.setcharacterencoding ("UTF-8"); Request.setcharacterencoding ("UTF-8"); PrintWriter out = Response.getwriter ();//system.out.println (1/0);//Beneficial exception. To check if the XMLHTTPREQUEST.STATUS!=200 branch statement in Demo1.jsp is available in string Username=request.getparameter ("UserName");//Get "UserName" System.out.println ("Handles asynchronous authentication in demo1.jsp, UserName is:" +username), if ("admin". Equals (UserName)) {Out.print ("1");//"1" Indicates that username is not available.
} else {Out.print ("2");//"2" means username is available. }out.flush (); Out.close ();} catch (Exception e) {e.printstacktrace (); Response.setstatus (405);}} /** * Processing Asynchronous validation in demo2.jsp * * @author Gaohuanjie */public void DoPost (HttpServletRequest request, HttpServletResponse Respon SE) throws Servletexception, IOException {try{response.setcharacterencoding ("UTF-8"); Request.setcharacterencoding ( "UTF-8"); PrintWriter out = Response.getwriter ();//system.out.println (1/0);//beneficial exception to check demo2.jsp xmlhttprequest.status!= Whether a 200 branch statement is available in string Username=request.getparameter ("UserName");//gets "UserName" System.out.println (" Handles asynchronous validation in demo2.jsp, UserName: "+username", if ("admin". Equals (UserName)) {Out.print ("1");//"1" means UserName is not available. } else {Out.print ("2");//"2" means username is available. }out.flush (); Out.close ();} catch (Exception e) {e.printstacktrace (); Response.setstatus (405);}}}
Code 5--web.xml File:
<?xml version= "1.0" encoding= "UTF-8"? ><web-app xmlns:xsi= "Http://www.w3.org/2001/XMLSchema-instance" xmlns= "Http://java.sun.com/xml/ns/javaee" xmlns:web= "http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi: schemalocation= "Http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id= "Webapp_ ID "version=" 2.5 "><servlet>    <servlet-name>AjaxCheckUserNameServlet</servlet-name>    <servlet-class>com.ghj.packagofserlet.AjaxCheckUserNameServlet</servlet-class></servlet>< servlet-mapping>    <servlet-name>AjaxCheckUserNameServlet</servlet-name>    <url-pattern >/AjaxCheckUserNameServlet</url-pattern></servlet-mapping>  <welcome-file-list>    <welcome-file>index.jsp</welcome-file></welcome-file-list></web-app>
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The use of traditional methods in Web pages to realize the specific interpretation of asynchronous verification