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Detailed explanation of traditional JavaScript methods to implement asynchronous verification_javascript skills

WBOY
WBOYOriginal
2016-05-16 15:18:471300browse

When learning JavaScript asynchronous verification, you often start with the most traditional XMLHttpRequest. This article will talk about the understanding of traditional verification:
Code 1index.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"> 
<html> 
  <head> 
    <title>如何使用传统方法异步验证用户名的唯一性</title> 
    <script type="text/javascript"> 
      function goDemo(pageName){ 
        window.location.href='<%=basePath%>'+pageName; 
      } 
    </script> 
  </head> 
  
  <body> 
    <center style="margin-top: 10%"><font style="color: red;font-size: 18pt;font-weight: bold;">如何使用传统方法异步验证用户名的唯一性</font></center><br> 
    例子一：<input type="button" value="例子一" onclick="goDemo('demo1.jsp');"/><br><br> 
    例子二：<input type="button" value="例子二" onclick="goDemo('demo2.jsp');"/><br><br> 
    例子一与例子二的区别：两者都实现了使用传统方法异步验证用户名的唯一性的功能，区别在于使用的servlet中的的方法不同："例子一"使用的servlet中的doGet方法；"例子二"使用的servlet中的doPost方法。 
  </body> 
</html>

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"> 
<html> 
  <head> 
    <title>使用的servlet中的doGet方法</title> 
    <script type="text/javascript"> 
      function checkUserName(){ 
        var value=document.getElementById("userName").value; 
        if(value==""){ 
          document.getElementById("showUserName").innerHTML="<font size=\"2\" color=red>用户名不能为空！！！</font>"; 
        }else{ 
          var xmlHttpRequest = null; 
          if(window.XMLHttpRequest){/*适用于IE7以上（包括IE7）的IE浏览器、火狐浏览器、谷歌浏览器和Opera浏览器*/ 
            xmlHttpRequest = new XMLHttpRequest();//创建XMLHttpRequest 
          }else if(window.ActiveXObject){/*适用于IE6.0以下（包括IE6.0）的IE浏览器*/ 
            xmlHttpRequest = new ActiveXObject("Microsoft.XMLHTTP"); 
          }//第一步：创建XMLHttpRequest对象，请求未初始化 
   
          xmlHttpRequest.onreadystatechange = function (){//readyState值发生改变时XMLHttpRequest对象激发一个readystatechange事件,进而调用后面的函数 
            if(xmlHttpRequest.readyState==1){ 
              xmlHttpRequest.send();//第三步：发送请求，也可以为xmlHttpRequest.send(null) 
            } 
            if(xmlHttpRequest.readyState==2){ 
              console.log("send()方法已执行，请求已发送到服务器端，但是客户端还没有收到服务器端的响应。"); 
            } 
            if(xmlHttpRequest.readyState==3){ 
              console.log("已经接收到HTTP响应头部信息，但是消息体部分还没有完全接收结束。"); 
            } 
            if(xmlHttpRequest.readyState==4){//客户端接收服务器端信息完毕。第四步：处理服务器端发回来的响应信息 
              if(xmlHttpRequest.status==200){//与Servlet成功交互 
                console.log("客户端已完全接收服务器端的处理响应。"); 
                var responseValue=xmlHttpRequest.responseText; 
                if(responseValue==1){ 
                  document.getElementById("showUserName").innerHTML="<font size=\"2\" color=\"red\"> 用户名已被使用！</font>"; 
                }else if(responseValue==2){ 
                  document.getElementById("showUserName").innerHTML="<font size=\"2\" color=\"green\"> 用户名有效！！！</font>"; 
                } 
              }else{//与Servlet交互出现问题 
                document.getElementById("showUserName").innerHTML="<font size=\"2\" color=\"red\">请求发送失败！</font>"; 
              } 
            } 
          }; 
           
          if(xmlHttpRequest.readyState==0){ 
            xmlHttpRequest.open("get","<%=basePath%>AjaxCheckUserNameServlet&#63;userName="+value,true);//第二步：完成请求初始化，提出请求。open方法中的三个参数分别是：请求方式、路径、是否异步（true表示异步，false表示同步） 
          } 
        } 
      } 
    </script> 
  </head> 
 
  <body> 
    <center style="margin-top: 10%"><font style="color: red;font-size: 18pt;font-weight: bold;">使用的servlet中的doGet方法</font><br><br> 
         用户名：<input type="text" id="userName" name="userName" size="27" onblur="checkUserName();"> 
      <font size="2" id="showUserName"> *用户名必填，具有唯一性。</font> 
    </center> 
  </body> 
</html>

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"> 
<html> 
  <head> 
    <title>使用的servlet中的doPost方法</title> 
    <script type="text/javascript"> 
      function checkUserName(){ 
        var value=document.getElementById("userName").value; 
        if(value==""){ 
          document.getElementById("showUserName").innerHTML="<font size=\"2\" color=red>用户名不能为空！！！</font>"; 
        }else{ 
          var xmlHttpRequest = null; 
          if(window.XMLHttpRequest){/*适用于IE7以上（包括IE7）的IE浏览器、火狐浏览器、谷歌浏览器和Opera浏览器*/ 
            xmlHttpRequest = new XMLHttpRequest();//创建XMLHttpRequest 
          }else if(window.ActiveXObject){/*适用于IE6.0以下（包括IE6.0）的IE浏览器*/ 
            xmlHttpRequest = new ActiveXObject("Microsoft.XMLHTTP"); 
          }//第一步：创建XMLHttpRequest对象，请求未初始化 
   
          xmlHttpRequest.onreadystatechange = function (){//readyState值发生改变时XMLHttpRequest对象激发一个readystatechange事件,进而调用后面的函数 
            if(xmlHttpRequest.readyState==1){ 
              xmlHttpRequest.send();//第三步：发送请求，也可以为xmlHttpRequest.send(null) 
            } 
            if(xmlHttpRequest.readyState==2){ 
              console.log("send()方法已执行，请求已发送到服务器端，但是客户端还没有收到服务器端的响应。"); 
            } 
            if(xmlHttpRequest.readyState==3){ 
              console.log("已经接收到HTTP响应头部信息，但是消息体部分还没有完全接收结束。"); 
            } 
            if(xmlHttpRequest.readyState==4){//客户端接收服务器端信息完毕。第四步：处理服务器端发回来的响应信息 
              if(xmlHttpRequest.status==200){//与Servlet成功交互 
                console.log("客户端已完全接收服务器端的处理响应。"); 
                var responseValue=xmlHttpRequest.responseText; 
                if(responseValue==1){ 
                  document.getElementById("showUserName").innerHTML="<font size=\"2\" color=\"red\"> 用户名已被使用！</font>"; 
                }else if(responseValue==2){ 
                  document.getElementById("showUserName").innerHTML="<font size=\"2\" color=\"green\"> 用户名有效！！！</font>"; 
                } 
              }else{//与Servlet交互出现问题 
                document.getElementById("showUserName").innerHTML="<font size=\"2\" color=\"red\">请求发送失败！</font>"; 
              } 
            } 
          }; 
           
          if(xmlHttpRequest.readyState==0){ 
            xmlHttpRequest.open("post","<%=basePath%>AjaxCheckUserNameServlet&#63;userName="+value,true);//第二步：完成请求初始化，提出请求。open方法中的三个参数分别是：请求方式、路径、是否异步（true表示异步，false表示同步） 
          } 
        } 
      } 
    </script> 
  </head> 
  
  <body> 
    <center style="margin-top: 10%"><font color="red" size="5"><strong>使用的servlet中的doPost方法</strong></font><br><br> 
         用户名：<input type="text" id="userName" name="userName" size="27" onblur="checkUserName()"> 
      <font size=2 id="showUserName"> *用户名必填，具有唯一性。</font> 
    </center> 
  </body> 
</html>

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 = 6387744976765210524L; 
 
  /** 
   * 处理demo1.jsp中异步验证 
   * 
   * @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);//故意出现异常，以检查demo1.jsp中xmlHttpRequest.status!=200的分支语句是否可用 
      String userName=request.getParameter("userName");//获取“用户名” 
      System.out.println("处理demo1.jsp中异步验证，用户名为："+userName); 
      if ("admin".equals(userName)) { 
        out.print("1");//“1”表示用户名不可用。  
      } else { 
        out.print("2");//“2”表示用户名可用。 
      } 
      out.flush(); 
      out.close(); 
    }catch (Exception e) { 
      e.printStackTrace(); 
      response.setStatus(405); 
    } 
  } 
   
  /** 
   * 处理demo2.jsp中异步验证 
   * 
   * @author GaoHuanjie 
   */ 
  public void doPost(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);//故意出现异常，以检查demo2.jsp中xmlHttpRequest.status!=200的分支语句是否可用 
      String userName=request.getParameter("userName");//获取“用户名” 
      System.out.println("处理demo2.jsp中异步验证，用户名为："+userName); 
      if ("admin".equals(userName)) { 
        out.print("1");//“1”表示用户名不可用。 
      } else { 
        out.print("2");//“2”表示用户名可用。 
      } 
      out.flush(); 
      out.close(); 
    }catch (Exception e) { 
      e.printStackTrace(); 
      response.setStatus(405); 
    } 
  } 
}

Code 5web.xml file: 

<&#63;xml version="1.0" encoding="UTF-8"&#63;> 
<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>

The above is the detailed code for implementing asynchronous verification using traditional methods. I hope it will be helpful to everyone's learning.

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