A detailed analysis of JavaScript traditional methods to implement asynchronous verification _javascript skills

Learning JavaScript Asynchronous checksums is often learned from the most traditional xmlhttprequest, and this article discusses the understanding of traditional checksums:
Code 1index.jsp files:

<%@ 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 2demo1.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 3demo2.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 4ajaxcheckusernameservlet.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 = 638774497676 
 
  5210524L; /** * Processing demo1.jsp Asynchronous Validation * * @author Gaohuanjie/public void doget (HttpServletRequest request, Httpserv 
      Letresponse response) throws Servletexception, IOException {try{response.setcharacterencoding ("UTF-8"); 
      Request.setcharacterencoding ("UTF-8"); 
      PrintWriter out = Response.getwriter (); System.out.println (1/0);//intentionally unexpected exception to check whether the branch statement xmlhttprequest.status!=200 in Demo1.jsp is available with String username= 
      Request.getparameter ("UserName")//Get "username" System.out.println ("Processing demo1.jsp asynchronous authentication, Username:" +username); if ("admin". Equals (UserName)) {
        Out.print ("1");//"1" indicates 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); demo2.jsp Asynchronous Validation * * @author Gaohuanjie/public void DoPost (HttpServletRequest re)/** * processing Quest, HttpServletResponse response) throws Servletexception, IOException {try{response.setcharacterencoding ( 
      "UTF-8"); 
      Request.setcharacterencoding ("UTF-8"); 
      PrintWriter out = Response.getwriter (); System.out.println (1/0);//intentionally unexpected exception to check whether the branch statement xmlhttprequest.status!=200 in Demo2.jsp is available with String username= 
      Request.getparameter ("UserName")//Get "username" System.out.println ("Processing demo2.jsp asynchronous authentication, Username:" +username); 
      if ("admin". Equals (UserName)) {Out.print ("1");//"1" indicates 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 5web.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> 

The above is the use of traditional methods to implement the detailed code of asynchronous checksum, I hope to help you learn.