验证码的实现

package util;

import java.io.*;
import java.net.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.awt.*;
import java.awt.image.*;
import java.util.*;
import javax.imageio.*;
/**
 *
 * <p>Title: 实验室申报系统</p>

 *
 * @version 2.0
 */
public class Image extends HttpServlet {

    /**
     *
     * @param request HttpServletRequest
     * @param response HttpServletResponse
     * @throws ServletException
     * @throws IOException
     */
    protected void processRequest(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        response.setContentType("image/jpeg");
        response.setHeader("Pragma","No-cache");
        response.setHeader("Cache-Control","no-cache");
        response.setDateHeader("Expires", 0);
        HttpSession session=request.getSession();
        // 在内存中创建图象
        int width=42, height=17;
        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.BOLD,16));
//画边框
//g.setColor(new Color());
//g.drawRect(0,0,width-1,height-1);
// 随机产生120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<120;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 rand = request.getParameter("rand");
//rand = rand.substring(0,rand.indexOf("."));
//        String sRand="";//原来的设置代码
        char [] rands=generateCheckCode();
//        for (int i=0;i<4;i++){
//            String rand=String.valueOf(random.nextInt(10));//原来的设置代码
//            sRand+=rand;//原来的设置代码
            // 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,9*i+2+2,12);////原来的设置代码

              g.drawString(""+rands[0],9*0+2+2,14);
              g.drawString(""+rands[1],9*1+2+2,14);
              g.drawString(""+rands[2],9*2+2+2,14);
              g.drawString(""+rands[3],9*3+2+2,14);
//        }
// 将认证码存入SESSION
//        session.setAttribute("rand",sRand);//原来的代码
        session.setAttribute("rand",new String(rands));

// 图象生效
          g.dispose();
          ServletOutputStream responseOutputStream =response.getOutputStream();//first none
          // 输出图象到页面
          ByteArrayOutputStream bos=new ByteArrayOutputStream();
//          ImageIO.write(image, "JPEG", response.getOutputStream());//原来的设置代码
           ImageIO.write(image, "JPEG", bos);
          //以下关闭输入流！first none
          byte[] buf=bos.toByteArray();
          response.setContentLength(buf.length);
          responseOutputStream.write(buf);
          bos.close();
          responseOutputStream.close();
//          responseOutputStream.flush();//原来的设置代码
//          responseOutputStream.close();//原来的设置代码
    }
    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);
    }
    // <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
    /** Handles the HTTP <code>GET</code> method.
     * @param request servlet request
     * @param response servlet response
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        processRequest(request, response);
    }

    /** Handles the HTTP <code>POST</code> method.
     * @param request servlet request
     * @param response servlet response
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {
        processRequest(request, response);
    }

    /** Returns a short description of the servlet.
     */
    public String getServletInfo() {
        return "有问题请和weibei@yeah.net联系";
    }
    private char [] generateCheckCode()
    {
        String chars="23456789abcdefghijknpqrstuvwxyz";//取消了有疵议的0,0以及1,l
        char[] rands=new char[4];
        for(int i=0;i<4;i++)
        {
            int rand=(int)(Math.random()*31);
            rands[i]=chars.charAt(rand);
        }
        return rands;
    }
    // </editor-fold>
}