servlet生成验证码

package com.mweb.user.servlet;  
   
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.ServletConfig;  
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  
{  
   
    @Override  
    public void init(ServletConfig config) throws ServletException  
    {  
        // TODO Auto-generated method stub  
        super.init(config);  
    }  
   
    /** 
     * 
     */  
    private static final long serialVersionUID = -8924942016876830055L;  
   
    public void doGet(HttpServletRequest req, HttpServletResponse resp)  
            throws ServletException, IOException  
    {  
        doPost(req, resp);  
    }  
   
    /** 
     * @see javax.servlet.http.HttpServlet#void 
     *      (javax.servlet.http.HttpServletRequest, 
     *      javax.servlet.http.HttpServletResponse) 
     */  
    public void doPost(HttpServletRequest req, HttpServletResponse resp)  
            throws ServletException, IOException  
    {  
   
        // 首先设置页面不缓存  
        resp.setHeader("Pragma", "No-cache");  
        resp.setHeader("Cache-Control", "no-cache");  
        resp.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  
        req.getSession().setAttribute("randcode", sRand);  
        // 使图像生效  
        g.dispose();  
        // 输出图像到页面  
        ImageIO.write(image, "JPEG", resp.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);  
    }  
}