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; // 2// 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;// 200

        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;
        }

}