servlet产生验证码

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);
    }
}