servlet生成随机验证码

 package com.cgyue;

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

 /**
  * 生成图形验证码的Servlet
  */
 public class ImageCodeMakerServlet extends HttpServlet {  

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

     /**
      * @see javax.servlet.http.HttpServlet#void
      *      (javax.servlet.http.HttpServletRequest,
      *      javax.servlet.http.HttpServletResponse)
      */
     public void doPost(HttpServletRequest request, HttpServletResponse response)
             throws ServletException, IOException {
         // 首先设置页面不缓存
         response.setHeader("Pragma", "No-cache");
         response.setHeader("Cache-Control", "no-cache");
         response.setDateHeader("Expires", 0);  

         // 定义图片的宽度和高度
         int width = 90, height = 40;
         // 创建一个图像对象
         BufferedImage image = new BufferedImage(width, height,
                 BufferedImage.TYPE_INT_RGB);
         // 得到图像的环境对象
         Graphics g = image.createGraphics();  

         Random random = new Random();
         // 用随机颜色填充图像背景
         g.setColor(getRandColor(180, 250));
         g.fillRect(0, 0, width, height);
         for (int i = 0; i < 5; i++) {
             g.setColor(getRandColor(50, 100));
             int x = random.nextInt(width);
             int y = random.nextInt(height);
             g.drawOval(x, y, 4, 4);
         }
         // 设置字体，下面准备画随机数
         g.setFont(new Font("", Font.PLAIN, 40));
         // 随机数字符串
         String sRand = "";
         for (int i = 0; i < 4; i++) {
             // 生成四个数字字符
             String rand = String.valueOf(random.nextInt(10));
             sRand += rand;
             // 生成随机颜色
             g.setColor(new Color(20 + random.nextInt(80), 20 + random
                     .nextInt(100), 20 + random.nextInt(90)));
             // 将随机数字画在图像上
             g.drawString(rand, (17 + random.nextInt(3)) * i + 8, 34);  

             // 生成干扰线
             for (int k = 0; k < 12; k++) {
                 int x = random.nextInt(width);
                 int y = random.nextInt(height);
                 int xl = random.nextInt(9);
                 int yl = random.nextInt(9);
                 g.drawLine(x, y, x + xl, y + yl);
             }
         }  

         // 将生成的随机数字字符串写入Session
         request.getSession().setAttribute("randcode", sRand);
         // 使图像生效
         g.dispose();
         // 输出图像到页面
         ImageIO.write(image, "JPEG", response.getOutputStream());
     }  

     /**
      * 产生一个随机的颜色
      * @param fc    颜色分量最小值
      * @param bc    颜色分量最大值
      * @return
      */
     public 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);
     }
 }