一段利用session生成随即验证码得代码分享

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 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;


public class Check extends HttpServlet ...{

   private static int WIDTH=60;
   private static int HEIGHT=20;
    
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException ...{
          HttpSession session=request.getSession();
          response.setContentType("image/jpeg");
          ServletOutputStream sos=response.getOutputStream();
          
          //设置浏览器不要缓存图片
          response.setHeader("Pragma", "No-cache");
          response.setHeader("Cache-Control", "no-cache");
          response.setDateHeader("Expires", 0);
          
          //创建内存图像并获得图像上下文
          BufferedImage image=new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB);
          Graphics g=image.getGraphics();
          
          //产生随即得验证码
          char[] rands=this.generateCheckCode();
          //产生图像
          this.drawBackground(g);
          this.drawRands(g, rands);
          
          //结束图像得绘制过程，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);
          bos.write(buf);
          bos.close();
          
          //将验证码放入到session中
          session.setAttribute("check_code", new String(rands));
          
          
    }
    private char[] generateCheckCode()...{
        //定义验证码得字符表
        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(i);
        }
        return rands;
    }
    
    
    private void drawRands(Graphics g, char[] rands)...{
        g.setColor(Color.BLACK);
        g.setFont(new Font(null,Font.ITALIC|Font.BOLD,18));
        g.drawString(""+rands[0],1,17);
        g.drawString(""+rands[0],16,15);
        g.drawString(""+rands[0],31,18);
        g.drawString(""+rands[0],46,16);
        
        
    }
    
    private void drawBackground(Graphics g)...{
        //画背景
        g.setColor(new Color(0xDCDCDC));
        g.fillRect(0, 0, WIDTH, HEIGHT);
        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);
        }
    }
    

}