验证码

   1.  <％@ page contentType="image/jpeg" import="java.awt.*,   
   2. java.awt.image.*,java.util.*,javax.imageio.*" ％>    
   3. <％    
   4. // 在内存中创建图象    
   5. int width=60, height=20;    
   6. BufferedImage image = new BufferedImage(width, height,    
   7. BufferedImage.TYPE_INT_RGB);    
   8.   
   9. // 获取图形上下文    
  10. Graphics g = image.getGraphics();    
  11.   
  12. // 设定背景色    
  13. g.setColor(new Color(0xDCDCDC));    
  14. g.fillRect(0, 0, width, height);    
  15.   
  16. //画边框    
  17. g.setColor(Color.black);    
  18. g.drawRect(0,0,width-1,height-1);    
  19.   
  20. // 取随机产生的认证码(4位数字)    
  21. String rand = request.getParameter("rand");    
  22. rand = rand.substring(0,rand.indexOf("."));    
  23. switch(rand.length())    
  24. {    
  25. case 1: rand = "000"+rand; break;    
  26. case 2: rand = "00"+rand; break;    
  27. case 3: rand = "0"+rand; break;    
  28. default: rand = rand.substring(0,4); break;    
  29. }    
  30.   
  31. // 将认证码存入SESSION    
  32. session.setAttribute("rand",rand);    
  33.   
  34. // 将认证码显示到图象中    
  35. g.setColor(Color.black);    
  36. Integer tempNumber = new Integer(rand);    
  37. String numberStr = tempNumber.toString();    
  38.   
  39. g.setFont(new Font("Atlantic Inline",Font.PLAIN,18));    
  40. String Str = numberStr.substring(0,1);    
  41. g.drawString(Str,8,17);    
  42.   
  43. Str = numberStr.substring(1,2);    
  44. g.drawString(Str,20,15);    
  45. Str = numberStr.substring(2,3);    
  46. g.drawString(Str,35,18);    
  47.   
  48. Str = numberStr.substring(3,4);    
  49. g.drawString(Str,45,15);    
  50.   
  51. // 随机产生88个干扰点，使图象中的认证码不易被其它程序探测到    
  52. Random random = new Random();    
  53. for (int i=0;i<20;i++)    
  54. {    
  55. int x = random.nextInt(width);    
  56. int y = random.nextInt(height);    
  57. g.drawOval(x,y,0,0);    
  58. }    
  59.   
  60. // 图象生效    
  61. g.dispose();    
  62.   
  63. // 输出图象到页面    
  64. ImageIO.write(image, "JPEG", response.getOutputStream());    
  65. ％>