动态验证码的生成

package com.javaee.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.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
* 动态验证码的生成
*
* @author George
*
*/
public class ImageServlet extends HttpServlet {

    public Color getRandColor(int fc, int bc) {// 给定范围获得随机颜色
        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);
    }

    protected void doGet(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {

        // 在内存中创建图象
        int width = 60, height = 20;
        BufferedImage image = new BufferedImage(width, height,
                BufferedImage.TYPE_INT_RGB);

        // 获取图形上下文
        Graphics g = image.getGraphics();

        // 生成随机类
        Random random = new Random();

        // 设定背景色
        g.setColor(getRandColor(200, 250));
        g.fillRect(0, 0, width, height);

        // 设定字体
        g.setFont(new Font("Times New Roman", Font.PLAIN, 18));

        // 画边框
        // g.setColor(new Color());
        // g.drawRect(0,0,width-1,height-1);

        // 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
        g.setColor(getRandColor(160, 200));
        for (int i = 0; i < 155; i++) {
            int x = random.nextInt(width);
            int y = random.nextInt(height);
            int xl = random.nextInt(12);
            int yl = random.nextInt(12);
            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(random.nextInt(10));
            sRand += rand;
            // 将认证码显示到图象中
            g.setColor(new Color(20 + random.nextInt(110), 20 + random
                    .nextInt(110), 20 + random.nextInt(110))); // 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.drawString(rand, 13 * i + 6, 16);
        }

        // 将认证码存入SESSION
//        session.setAttribute("rand", sRand);

        // 图象生效
        g.dispose();

        // 输出图象到页面
        ImageIO.write(image, "JPEG", response.getOutputStream());
       
    }

    protected void doPost(HttpServletRequest arg0, HttpServletResponse arg1)
            throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(arg0, arg1);
    }

}