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);  
    }  
}