校验码生成

下面的代码都是抄过来的，不怎么理解，用的时候方便copy

在jsp页面写上<img src="authImg" height:20px; width:60px"/>，就会自动的将request中的authImg加进去，不知道怎么回事，应该是会自动调用的。高和宽的值也要和代码中的一致。

代码如下，这段代码会生成随机的字母与数字混合的验证码：

public class AuthImg extends HttpServlet {

 private static final long serialVersionUID = -8281845659081613239L;

 private Font mFont = new Font("Times New Roman", Font.PLAIN, 18);

 public void init() throws ServletException {
 }

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  response.setContentType("image/jpeg");
  ServletOutputStream out = response.getOutputStream();

  int width = 60, height = 20;
  BufferedImage image = new BufferedImage(width, height,
    BufferedImage.TYPE_INT_RGB);

  Graphics g = image.getGraphics();
  Random random = new Random();

  g.setColor(getRandColor(200, 250));
  g.fillRect(0, 0, width, height);

  g.setFont(mFont);

  g.setColor(getRandColor(160, 200));
  for (int i = 0; i < 155; i++) {
   int x = random.nextInt(width);
   int y = random.nextInt(height);
   int xl = random.nextInt(12);
   int yl = random.nextInt(12);
   g.drawLine(x, y, x + xl, y + yl);
  }

  String rand = RandomChar.getChars(4, 4);
  char c;
  for (int i = 0; i < 4; i++) {
   c = rand.charAt(i);
   g.setColor(new Color(20 + random.nextInt(110), 20 + random
     .nextInt(110), 20 + random.nextInt(110)));
   g.drawString(String.valueOf(c), 13 * i + 6, 16);
  }
  HttpSession seesion = request.getSession();
  seesion.setAttribute("authCode", rand);
  JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);
  encoder.encode(image);
  out.close();
 }

 public void doPost(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  doGet(request, response);
 }

 public void destroy() {
 }

 private Color getRandColor(int fc, int bc) {
  Random random = new Random();
  if (fc > 255) {
   fc = 255;
  }
  if (bc > 255) {
   bc = 255;
  }
  int r = fc + random.nextInt(bc - fc);
  int g = fc + random.nextInt(bc - fc);
  int b = fc + random.nextInt(bc - fc);
  return new Color(r, g, b);
 }
}

代码中涉及到一个类RandomChar。代码如下

public class RandomChar {
 private static final String CHAR_ALL = "qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM";

 private static final String CHAR_LOWERCASE = "qwertyuiopasdfghjklzxcvbnm";

 private static final String CHAR_UPPERCASE = "QWERTYUIOPLAKSJDHFGZXCVBNM";

 private static final String NUMBERS = "0123456789";

 private static final String ALL = "qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM1234567890";

 private static final String CHAR_SPECIAL_ALL = "qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM~!@#$%^&*";

 public static final int RANDOM_CHAR_UPPERCASE = 0;

 public static final int RANDOM_CHAR_LOWERCASE = 1;

 public static final int RANDOM_CHAR_ALL = 2;

 public static final int RANDOM_NUMBERS = 3;

 public static final int RANDOM_ALL = 4;

 public static final int RANDOM_SPECIAL_ALL = 5;

 public static String getChars(int MOD, int count) {

  Random r = new Random();

  int i = 0;
  String random_source = null;
  switch (MOD) {
  case RANDOM_CHAR_UPPERCASE:
   random_source = CHAR_UPPERCASE;
   break;
  case RANDOM_CHAR_LOWERCASE:
   random_source = CHAR_LOWERCASE;
   break;
  case RANDOM_CHAR_ALL:
   random_source = CHAR_ALL;
   break;
  case RANDOM_NUMBERS:
   random_source = NUMBERS;
   break;
  case RANDOM_ALL:
   random_source = ALL;
   break;
  case RANDOM_SPECIAL_ALL:
   random_source = CHAR_SPECIAL_ALL;
   break;
  default:
   random_source = CHAR_SPECIAL_ALL;
   break;
  }

  int c = random_source.length();
  String result = "";

  while (i < count) {
   int v = Math.abs(r.nextInt()) % c;
   result += random_source.substring(v, v + 1);
   i++;
  }
  return result;
 }
}