详解javascript传统方法实现异步校验_javascript技巧

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> 
<% 
  String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+request.getContextPath()+"/"; 
%> 
 
 
   
     
    

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); 
    } 
  } 
} 

<?xml version="1.0" encoding="UTF-8"?> 
 
 
   
    AjaxCheckUserNameServlet 
    com.ghj.packagofserlet.AjaxCheckUserNameServlet 
   
 
   
    AjaxCheckUserNameServlet 
    /AjaxCheckUserNameServlet 
   
  
   
    index.jsp