java 实现验证码

 package edu.zzuli.common;

 import java.awt.Color;
 import java.awt.Font;
 import java.awt.Graphics2D;
 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;

 /**
  * @author tianshaojie
  * @date 2011-1-7
  * @discription :
  */
 public class VerifyCodeServlet extends HttpServlet {

         private static final long serialVersionUID = -7713673953332628094L;

         private Font mFont = new Font("Arial Black", Font.BOLD, 15); // 设置字体new  Font("Arial Black",  Font.PLAIN, 15);

         private int lineWidth = 5; //// 干扰线的长度=1.414*lineWidth

         private int width = 60; // 定义图形大小

         private int height = 20; // 定义图形大小

         private int count = 300;//

         private Color getRandColor(int fc, int bc) { // 取得给定范围随机颜色
                 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);
         }

         @SuppressWarnings("unused")
         private char random2Char(int random) {
                 char c = '0';
                 if (random >= 0 && random <= 9) {
                         c = (char) (random + 48);
                 } else if (random >= 10 && random <= 35) {
                         c = (char) (random + 55);
                 } else if (random >= 36 && random <= 61) {
                         c = (char) (random + 61);
                 }
                 return c;
         }

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

         public void doGet(HttpServletRequest request, HttpServletResponse response)
                         throws ServletException, IOException {
                 // response.reset();
                 // 设置页面不缓存
                 response.setHeader("Pragma", "No-cache");
                 response.setHeader("Cache-Control", "no-cache");
                 response.setDateHeader("Expires", 0);
                 response.setContentType("image/gif");
                 // 在内存中创建图象
                 BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

                 // 获取图形上下文
                 Graphics2D g = (Graphics2D) image.getGraphics();
                 // 生成随机类
                 Random random = new Random();
                 // 设定背景色
                 g.setColor(getRandColor(200, 250)); // ---1
                 g.fillRect(0, 0, width, height);

                 // 设定字体
                 g.setFont(mFont);

                 // 画边框
                 g.setColor(getRandColor(0, 20)); // ---2
                 g.drawRect(0, 0, width - 1, height - 1);

                 // 随机产生干扰线，使图象中的认证码不易被其它程序探测到
                 for (int i = 0; i < count; i++) {
                         g.setColor(getRandColor(150, 200)); // ---3
                         int x = random.nextInt(width - lineWidth - 1) + 1; // 保证画在边框之内
                         int y = random.nextInt(height - lineWidth - 1) + 1;
                         int xl = random.nextInt(lineWidth);
                         int yl = random.nextInt(lineWidth);
                         g.drawLine(x, y, x + xl, y + yl);
                 }

                 // 取随机产生的认证码(4位数字)
                 String sRand = "";

                 for (int i = 0; i < 4; i++) {
                         // String rand = String.valueOf(random2Char(random.nextInt(62)));
                         String rand = String.valueOf(random.nextInt(10));
                         sRand += rand;
                         // 将认证码显示到图象中,调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
                         g.setColor(new Color(20 + random.nextInt(130), 20 + random.nextInt(130), 20 + random.nextInt(130))); // --4--50-100
                         g.drawString(rand, (13 * i) + 6, 16);
                 }
                 // 将认证码存入SESSION
                 request.getSession().setAttribute(Constants_core.RANDOM_CHECKCODE, sRand);
                 // System.out.println("checkcode:"+sRand);
                 // 图象生效
                 g.dispose();
                 // 输出图象到页面
                 ImageIO.write(image, "PNG", response.getOutputStream());
         }

         public static String randomCheckCode(HttpServletRequest request) {
                 Random random = new Random();
                 String sRand = "";
                 for (int i = 0; i < 4; i++) {
                         String rand = String.valueOf(random.nextInt(10));
                         sRand += rand;
                 }
                 request.getSession().setAttribute(Constants_core.RANDOM_CHECKCODE, sRand);
                 return sRand;
         }

 }