验证码 Demo

         //设置响应头
         response.setCharacterEncoding("image/jpeg");
         int width=160;
         int height=40;
         BufferedImage image=new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
         Graphics g=image.getGraphics();
         Graphics2D g2d = (Graphics2D) g;
         g2d.setColor(Color.WHITE);
         g2d.fillRect(0, 0, width, height);
         g2d.setFont(new Font("宋体", Font.BOLD, 18));
          Random random=new Random();
         for(int i=0;i<4;i++)//获取随机四个汉字
         {
             Color c=new Color(random.nextInt(256), random.nextInt(256), random.nextInt(256));
             String s=GetStr();

             AffineTransform aff = new AffineTransform();
             aff.rotate(Math.random(),i*10,height-20);//旋转
             aff.scale(0.2+Math.random(), 0.2+Math.random());//缩放
             g2d.setTransform(aff);
             System.err.println(">:"+s);        

             g2d.setColor(c);
             g2d.drawString(s, i*10, height- 5);
         }

         for(int i=0;i<3;i++)    //干扰线
         {
             Color c=new Color(random.nextInt(256), random.nextInt(256), random.nextInt(256));
             g2d.setColor(c);
             g2d.drawLine(random.nextInt(width), random.nextInt(height), random.nextInt(width), random.nextInt(height));

         }
         g2d.dispose();//图片生效
         ImageIO.write(image, "jpeg", response.getOutputStream());//输出
         System.out.println("输出");
     }

     //获取汉字
     private static String GetStr()
     {
         String str = null;
         try {

             int hightPos, lowPos; // 定义高低位
             Random random = new Random();
             hightPos = (176 + Math.abs(random.nextInt(39)));//获取高位值
             lowPos = (161 + Math.abs(random.nextInt(93)));//获取低位值
             byte[] b = new byte[2];
             b[0] = (new Integer(hightPos).byteValue());
             b[1] = (new Integer(lowPos).byteValue());
             str = new String(b, "GBK");//转成中文

         } catch (Exception e) {
             e.printStackTrace();
         }
         return str;

     }

PS：写验证码不能把所有的都用上，这样就无法识别了，可以选择其中的几种进行，如写汉字只加干扰线，写字母加旋转等。