基于ajax实现验证码功能

%@ page contentType="image/jpeg; charset=utf-8" 
  language="java" import="java.util.*,java.awt.*,java.awt.image.*,javax.imageio.*" 
  pageEncoding="UTF-8"%> 
!-- 以上导入awt和awt.image包 --> 
%! 
  //获取随机颜色 
  public Color getColor(){ 
   Random random = new Random(); 
   //使用rgb()随机产生颜色 
   int r = random.nextInt(256); 
   int g = random.nextInt(256); 
   int b = random.nextInt(256); 
    
   return new Color(r,g,b); 
  } 
   
  //获取随机数字 产生一个4位数 
  public String getNum(){ 
   String str = ""; 
   Random random = new Random(); 
   for(int i = 0;i  4;i++){ 
    str += random.nextInt(10); //0-9 
   } 
   return str; 
  } 
%> 
 
% 
  /* 清除缓存 */ 
  response.setHeader("pragma", "mo-cache"); 
  response.setHeader("cache-control", "no-cache"); 
  response.setDateHeader("expires", 0); 
  //产生矩形框 
  BufferedImage image = new BufferedImage(80,30,BufferedImage.TYPE_INT_RGB); 
  //获取画笔工具 
  Graphics g = image.getGraphics(); 
  //设置矩形框的颜色 
  g.setColor(new Color(200,200,200)); 
  //设置坐标和宽高 
  g.fillRect(0, 0, 80, 30); 
     
  //随机产生干扰线 
  for(int i = 0;i  30;i++){ 
   Random random = new Random(); 
   int x = random.nextInt(80); 
   int y = random.nextInt(30); 
   int x1 = random.nextInt(x + 10); 
   int y1 = random.nextInt(y + 10); 
   //设置随机颜色 
   g.setColor(getColor()); 
   //画出来 
   g.drawLine(x, y, x1, y1); 
  } 
   
  //字的颜色和数字 
  g.setFont(new Font("Microsoft YaHei",Font.BOLD,16)); 
  g.setColor(Color.BLACK); 
  //获取随机数字 
  String checkNum = getNum(); 
   
  //给字拼接空格 
  StringBuffer sb = new StringBuffer(); 
  for(int i = 0;i  checkNum.length();i++){ 
   sb.append(checkNum.charAt(i) + " "); 
  } 
  //画出数字 
  g.drawString(sb.toString(), 15, 20); 
  //存入session域中 
  session.setAttribute("CHECKNUM", checkNum); //例如1010 
  //将图像以jpeg的形式通过字节流输出 
  ImageIO.write(image, "jpeg", response.getOutputStream()); 
  //清除缓存 
  out.clear(); 
  //放入body中 
  out = pageContext.pushBody(); 
%> 

%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> 
% 
String path = request.getContextPath(); 
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; 
%> 
 
!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 
html> 
 head> 
 base href="%=basePath%>" rel="external nofollow" > 
  
 title>验证码/title> 
  
 meta http-equiv="pragma" content="no-cache"> 
 meta http-equiv="cache-control" content="no-cache"> 
 meta http-equiv="expires" content="0">  
 meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> 
 meta http-equiv="description" content="This is my page"> 
 style type="text/css"> 
  table{ 
   margin: 100px auto; 
  } 
   
 /style> 
 /head> 
 
 body> 
  table border="0" align="center"> 
   tr> 
    td>验证码/td> 
    td>input type="text" name="checkcode" id="checkcodeID" maxlength="4" size="4">/td> 
    td>img alt="加载失败" src="image.jsp">/td> 
    td id="show">√√√/td> 
   /tr> 
  /table> 
 /body> 
 script type="text/javascript"> 
  //去除空格 
  function trim(str){ 
   //从左侧开始替换空格 
   str = str.replace(/^\s*/,""); 
   //从左侧开始替换空格 
   str = str.replace(/\s$/,""); 
   return str; 
  } 
  
 /script> 
 
 script type="text/javascript"> 
  //创建ajax对象 
  function createAjax(){ 
   var ajax = null; 
   try{ 
    ajax = new ActiveXObject("microsoft.xmlhttp"); 
   }catch(e){ 
    try{ 
     ajax = new XMLHttpRequest(); 
    }catch(e1){ 
     alert("请更换浏览器"); 
    } 
   } 
   return ajax; 
  } 
 /script> 
 
 
 script type="text/javascript"> 
  document.getElementById("checkcodeID").onkeyup = function(){ 
   var checkcode = this.value; 
   //去除空格 
   checkcode = trim(checkcode); 
   if(checkcode.length == 4){ 
    //获取ajax对象 
    var ajax = createAjax(); 
    //获取去空格的内容 
     
    var method = "POST"; 
    var url = "${pageContext.request.contextPath}/CheckcodeServlet?time="+new Date().getTime(); 
    //准备发送异步请求 
    ajax.open(method, url); 
    //设置请求头POST提交方式才需要 
    ajax.setRequestHeader("content-type", "application/x-www-form-urlencoded"); 
    //拼接实体内容 
    var content = "checkcode=" + checkcode;     
    //发送请求 
    ajax.send(content); 
     
    //监听服务器状态变化 
    ajax.onreadystatechange = function(){ 
     if(ajax.readyState == 4){ 
      if(ajax.status == 200){ 
       //获取服务器内容 
       var tip = ajax.responseText; 
       //获取图片路径 然后进行放入td中 
       var img = document.createElement("img"); 
       img.src = tip; 
       img.style.width = "14px"; 
       img.style.height = "14px"; 
       var td = document.getElementById("show"); 
       td.innerHTML = ""; 
       td.appendChild(img); 
      } 
     } 
    } 
     
   } 
    
  } 
 /script> 
/html> 

public class CheckcodeServlet extends HttpServlet { 
 @Override 
 protected void doPost(HttpServletRequest req, HttpServletResponse resp) 
   throws ServletException, IOException { 
  req.setCharacterEncoding("utf-8"); 
  resp.setContentType("text/html;charset=utf-8"); 
  //图片路径 
  String tip = "images/MsgError.gif"; 
   
  String checkcode = req.getParameter("checkcode"); 
  //测试 
  System.out.println(checkcode); 
  //获取session域中的数字 
  String checkcodeService = (String) req.getSession().getAttribute("CHECKNUM"); 
  //判断 
  if (checkcode.equals(checkcodeService)) { 
   tip = "images/MsgSent.gif"; 
  } 
  //输出路径 
  PrintWriter pw = resp.getWriter(); 
  pw.write(tip); 
  pw.flush(); 
  pw.close(); 
 } 
}