随机码生成

package com.authority.ui.web.servlet;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;


@SuppressWarnings("serial")
public class CheckCodeServlet extends HttpServlet
{

    private static int WIDTH             = 60;

    private static int HEIGHT            = 20;

    private String     CheckCode_Session = "CheckCode";

    /**
     * HttpServlet方法实现，验证码图片升成逻辑
     * 1.设置浏览器不要缓存此图片
     * 2.创建内存图象并获得其图形上下文
     * 3.产生随机的认证码
     * 4.产生图像
     * 5.结束图像的绘制过程，完成图像
     * 6.将图像输出到客户端
     * 7.将当前验证码存入到Session
     * 
     * @param request
     * @param response
     * @throws ServletException
     * @throws IOException
     */
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException
    {
        HttpSession session = request.getSession();

        //设置浏览器不要缓存此图片
        response.setContentType("image/jpeg");
        response.setHeader("Pragma", "No-cache");
        response.setHeader("Cache-Control", "no-cache");
        response.setDateHeader("Expires", 0);

        ServletOutputStream sos = response.getOutputStream();

        //创建内存图象并获得其图形上下文
        BufferedImage image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);

        Graphics g = image.getGraphics();

        //产生随机的认证码
        char[] rands = generateCheckCode();

        //产生图像
        drawBackground(g);
        drawRands(g, rands);

        //结束图像的绘制过程，完成图像
        g.dispose();

        //将图像输出到客户端
        ByteArrayOutputStream bos = new ByteArrayOutputStream();

        ImageIO.write(image, "JPEG", bos);

        byte[] buf = bos.toByteArray();
        response.setContentLength(buf.length);

        //下面的语句也可写成：bos.writeTo(sos);
        sos.write(buf);
        bos.close();
        sos.close();

        //将当前验证码存入到Session中
        session.setAttribute(CheckCode_Session, new String(rands));

        //直接使用下面的代码将有问题，Session对象必须在提交响应前获得
        //request.getSession().setAttribute("check_code",new String(rands));
    }

    /**
     * 生成验证码
     * 
     * @return
     */
    private char[] generateCheckCode()
    {
        //定义验证码的字符表
        //考虑到1和l难以区分,将l大写为L
        String chars = "0123456789abcdefghijkLmnopqrstuvwxyz";

        char[] rands = new char[4];
        for (int i = 0; i < 4; i++)
        {
            int rand = (int) (Math.random() * 36);
            rands[i] = chars.charAt(rand);
        }

        return rands;
    }

    /**
     * 生成图片
     * 
     * @param g
     * @param rands
     */
    private void drawRands(Graphics g, char[] rands)
    {

        g.setColor(Color.BLACK);
        g.setFont(new Font("Arial", Font.PLAIN, 15));

        //在不同的高度上输出验证码的每个字符    
        //1,10,20,30 左右位置，15高度
        g.drawString("" + rands[0], 3, 13);
        g.drawString("" + rands[1], 16, 13);
        g.drawString("" + rands[2], 29, 13);
        g.drawString("" + rands[3], 42, 13);
        //System.out.println(rands);
    }

    /**
     * 画干扰背景
     * 
     * @param g
     */
    private void drawBackground(Graphics g)
    {
        Random r = new Random();
        //画背景
        g.setColor(new Color(0xffffff));
        g.fillRect(0, 0, WIDTH, HEIGHT);
        //随机干扰点
        for (int x = 0; x < WIDTH; x++)
        {
            for (int y = 0; y < HEIGHT; y++)
            {
                int t = r.nextInt(3);
                if (t == 0)
                {
                    //蓝绿
                    g.setColor(new Color(200, 248, 248));
                    g.drawOval(x, y, 1, 0);
                }
                if (t == 1)
                {
                    //白
                    g.setColor(new Color(255, 255, 255));
                    g.drawOval(x, y, 1, 0);
                }
                if (t == 2)
                {
                    //淡紫
                    g.setColor(new Color(200, 200, 248));
                    g.drawOval(x, y, 1, 0);
                }
            }
        }

        //        for (int i = 0; i < 120; i++)
        //        {
        //            int x = (int) (Math.random() * WIDTH);
        //            int y = (int) (Math.random() * HEIGHT);
        //            int red = (int) (Math.random() * 255);
        //            int green = (int) (Math.random() * 255);
        //            int blue = (int) (Math.random() * 255);
        //            g.setColor(new Color(red, green, blue));
        //            g.drawOval(x, y, 1, 0);
        //        }

    }
    
    /**
     *         public void CreateImage(string Code)
        {
            System.Drawing.Text.PrivateFontCollection pfc = new System.Drawing.Text.PrivateFontCollection();
            pfc.AddFontFile( HttpContext.Current.Server.MapPath( "~/File/Font/arial.ttf")); //添加字体的集合

            int iwidth = (int)(Code.Length * 15);
            System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 24);
            Graphics g = Graphics.FromImage(image);

            Font f = new System.Drawing.Font(pfc.Families[0], 15,FontStyle.Bold, GraphicsUnit.Pixel);//创建font

            Brush b = new System.Drawing.SolidBrush(Color.White);

            g.Clear(Color.Blue);

            //画字
            g.DrawString(Code, f, b, 3, 3);
                        
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            image.Save(ms,System.Drawing.Imaging.ImageFormat.Jpeg);

            Response.ContentType = "image/Jpeg";
            Response.BinaryWrite(ms.ToArray());
            g.Dispose();
            image.Dispose();
        }
     * */

}