[求助]验证码问题：为何jsp显示的session值和servlet里面的session值不同？

kenvinp 2006-04-28 04:22:45



servlet:

=============

import java.io.IOException;

import javax.servlet.ServletException;



import javax.servlet.http.*;

import javax.servlet.ServletContext;

import java.io.OutputStream;

import java.util.Random;

import java.awt.*;

import java.awt.image.*;

import com.sun.image.codec.jpeg.*;

import webutil.*;

/**

 * @version  1.0

 * @author dennis

 */

public class Getshowimg extends HttpServlet {

 private String code;

 

 public void service(HttpServletRequest req, HttpServletResponse resp)

  throws ServletException, IOException {

   

   resp.setContentType("image/jpeg;charset=gb2312");

   int width=80, height=20;

   BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

   Graphics g = image.getGraphics();

   //以下填充背景颜色

   g.setColor(Color.decode("#66CCCF"));

   g.fillRect(0, 0, width, height);

   g.setColor(Color.decode("#01556B"));

   g.setFont(new Font("Times New Roman",Font.PLAIN,18));

// 生成随机类

   Random random = new Random();   

// 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);

   }

   

   String rstr = "";

   RandomStrg rst = new RandomStrg();

   rst.setCharset("a-zA-Z0-9");

   rst.setLength("6");

   

   

   try{

	   rst.generateRandomObject();

	   rstr= rst.getRandom();

	  

   }catch(Exception ex){

	   ex.printStackTrace();

	   

   }

   

   String sRand="";

   for (int i=0;i<rstr.length();i++){

       String rand=String.valueOf(rstr.charAt(i));

//       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+5,15);

   }

//   g.drawString(req.getParameter("yzm"),5,15);



   

   //g.drawString(rstr,5,15);

   g.dispose();    

   OutputStream toClient = resp.getOutputStream();

   JPEGImageEncoder encoder =JPEGCodec.createJPEGEncoder(toClient);

   encoder.encode(image);

            toClient.close();

 

   

            req.getSession().setAttribute("rstr",rstr);

            this.code = rstr;

            System.out.println(req.getSession().getAttribute("rstr"));

   }

 

   public String getCode(){

	   return this.code;

   }

   

   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);

   }

 

}







jsp:

=====

<form name = form1 method="post">



验证码：<input name="yzm" type="text" size="12"  id="yzm0"></td>

  <div id="yzm1" style="width:10" style="display:none"></div><IMG  id="img0" src="Getshowimg" vspace=3>

<input type=submit name=submit value="submit" onclick="javascript:return checkcode();" >

</form>

<%



out.println("session::"+session.getAttribute("rstr") );

%>



为何第一次打印的session值为空？？再刷新一次页面显示的session是上个servlet里面设置的值？？请问怎样才能第一次就显示和servlet里面的值一样啊？？