Using traditional methods in Web pages to implement asynchronous validation explanations

Learning JavaScript asynchronous checksum is often from the most traditional XMLHttpRequest, today Saturday, I will talk about the traditional calibration of the understanding:

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" >
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" >
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);//intentional exception to check demo1.jsp xmlhttprequest.status!= Whether the 200 branch statement is available in string Username=request.getparameter ("UserName");//Gets the "username" System.out.println (" Handles asynchronous authentication in demo1.jsp with the user name: "+username", if ("admin". Equals (UserName)) {Out.print ("1"), or "1" indicating that the user name is not available. } else {Out.print ("2");//"2" indicates that the user name 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);//intentional exception to check demo2.jsp xmlhttprequest.status!= Whether the 200 branch statement is available in string Username=request.getparameter ("UserName");//Gets the "username" System.out.println (" Handles asynchronous authentication in demo2.jsp with the user name: "+username", if ("admin". Equals (UserName)) {Out.print ("1"), or "1" indicating that the user name is not available. } else {Out.print ("2");//"2" indicates that the user name 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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