用ServletJSP动态生成英文、数字图像验证码

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Date;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class ValidateCode extends HttpServlet {

 // Process the HTTP Get request

 public void doGet(HttpServletRequest request, HttpServletResponse response)
   throws ServletException, IOException {
  // 设置页面不缓存
  response.setHeader("Pragma", "No-cache");
  response.setHeader("Cache-Control", "no-cache");
  response.setDateHeader("Expires", 0);

  // 设置图片的长宽
  int width = 62, height = 22;

  // // 创建内存图像
  BufferedImage image = new BufferedImage(width, height,
    BufferedImage.TYPE_INT_RGB);
  // 获取图形上下文
  Graphics g = image.createGraphics();

  // 设定图像背景色(因为是做背景，所以偏淡)
  g.setColor(getRandColor(180, 250));
  g.fillRect(0, 0, width, height);
  // 设置字体
  g.setFont(new Font("Times New Roman", Font.PLAIN, 17));

  // /设置默认生成4个验证码
  int length = 4;
  java.util.Random rand = new Random(); // 设置随机种子

  /*
   * if (request.getParameter("length") != null) { try { length =
   * Integer.parseInt(request.getParameter("length")); }catch
   * (NumberFormatException e) {} }
   */
  // 设置备选验证码:包括"a-z"和数字"0-9"
  String base = "abcdefghijklmnopqrstuvwxyz0123456789";
  int size = base.length();
  StringBuffer str = new StringBuffer();
  for (int i = 0; i < length; i++) {
   int start = rand.nextInt(size);
   String tmpStr = base.substring(start, start + 1);

   str.append(tmpStr);
   // 生成随机颜色(因为是做前景，所以偏深)
   g.setColor(getRandColor(10, 150));

   // 将此字画到图片上
   // g.drawString(str.toString(), 4, 17);
   g.drawString(tmpStr, 13 * i + 6 + rand.nextInt(5), 14 + rand
     .nextInt(6));

  }

  // 将认证码存入session
  request.getSession().setAttribute("valiCode", str.toString());

  // 图象生效
  g.dispose();

  // 输出图象到页面
  ImageIO.write(image, "JPEG", response.getOutputStream());

 }

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

 // 给定范围获得一个随机颜色
 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);
 }

}