Java 验证码详解

时间：2023-03-09 17:42:16
Java 验证码详解

　　1 使用Servlet实现验证码，涉及的知识点主要为java 绘图技术与session保存数据。

　　 HTML页面

 <html>

 <image src='images/logo1.jpg' /><hr/>

 <head><br/><title>登录</title> <br/><h1> 欢迎登录</h1></head>

 <body>

 <form action='/LoginValid/LoginVerify' method='post' >

 用户id：<input type='text' name='userid' value=''>

 用户密码：<input type='password' name='password' value=''>

 验证码：<input type='text' name='inputCode' />  <img id='imgObj' src='/LoginValid/CreateCode2' /><a href='javascript:changeImg()' >换一张</a>

 <input type='submit' value='登录' />

 </form>

 </body>

 <script type='text/javascript'>

 function changeImg() {  
var time = new Date(); 
document.getElementById('imgObj').src='/LoginValid/CreateCode2?d='+time;  
}

 </script>

 </html>

　　

　　生成验证码的工具类

 public class CodeUtil {

     //图片宽度

     private static final int IMG_W=120;

     //图片高度

     private static final int IMG_H=30;

     //验证码字符个数

     private static final int NUM_CHS=5;

     //验证码包含的具体字符

     private static char[] chs = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890".toCharArray();

     private static Random rand = new Random();

     //图片x轴，y轴的位置基数

     private static int codeX = 20;

     private static int codeY = 25;

     //字体大小

     private static int fontH = 25;

     public static Map<String, Object> generateImage()

     {

         BufferedImage image = new BufferedImage(IMG_W, IMG_H, BufferedImage.TYPE_INT_RGB);

         Graphics g = image.getGraphics();

         //设置图片背景色为白色

         g.setColor(Color.WHITE);

         g.fillRect(0, 0, IMG_W, IMG_H);

         //设置字体大小

         Font font = new Font("Fixedsys", Font.BOLD, fontH);

         g.setFont(font);

         //画边框

         g.setColor(Color.BLACK);

         g.drawRect(0, 0, IMG_W, IMG_H);

         g.setColor(Color.BLACK);

         //随机产生30条干扰线

         for(int i=0; i<30; i++)

         {

             int x = rand.nextInt(IMG_W);

             int y = rand.nextInt(IMG_H);

             int xl = rand.nextInt(20);

             int yl = rand.nextInt(20);

             g.drawLine(x, y, xl, yl);

         }

         StringBuilder sb = new StringBuilder();

         for(int i=0; i<NUM_CHS; i++)

         {

             //从字符串中随机获取一个字符

             String code = String.valueOf(chs[rand.nextInt(chs.length)]);

             //随机设置画笔颜色

             g.setColor(new Color(rand.nextInt(255),rand.nextInt(255),rand.nextInt(255)));

             g.drawString(code, (i+1)*codeX, codeY);

             sb.append(code);

         }

         Map<String, Object> map = new HashMap<String, Object>();

         map.put("code", sb.toString());

         map.put("codeImage", image);

         return map;

     }

 }

　　后台产生验证码的Servlet

         //禁止浏览器缓存随机图片

         response.setDateHeader("Expires",-1);

         response.setHeader("Cache-Control", "no-cache");

         response.setHeader("Pragma", "no-cache");

         //通知客户端以图片的方式打开发送过去的数据

         response.setHeader("Content-Type", "image/jpeg");

         Map<String, Object> map = CodeUtil.generateImage();

         //将验证码保存至session

         request.getSession().setAttribute("checkCode", map.get("code"));

         ImageIO.write((RenderedImage)map.get("codeImage"), "jpg", response.getOutputStream());

　　后台验证用户输入的验证码与显示的是否一致的Servlet类

         HttpSession session = request.getSession();

         String seCode = (String)session.getAttribute("checkCode");

         String inputCode = (String)request.getParameter("inputCode");

         if(seCode.equals(inputCode))

         {

             request.getRequestDispatcher("/Main").forward(request, response);

         }

         else

         {

             request.getRequestDispatcher("/Err").forward(request, response);

         }

　　博客参考：https://www.cnblogs.com/nanyangke-cjz/p/7049281.html 

　　

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