［２００分］在jsp页面怎么生成图片的校验码，用于用户的登陆校验!等

［２００分］在jsp页面如何生成图片的校验码，用于用户的登陆校验!!急等
在jsp页面如何生成图片的校验码，用于用户的登陆校验!!急等
    最好有现成的代码！如果可以另开100分的一帖！！！

------解决方案--------------------
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpServlet;
import javax.servlet.ServletOutputStream;
import javax.servlet.ServletException;
import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.util.Random;
import java.io.IOException;

/**
* @author <a href= "mailto:jade_yuan@hotmail.com "> Jade Yuan </a>
* @version 2006-3-9 18:34:36
*/
public class ImageServlet extends HttpServlet {
private static final String CONTENT_TYPE = "image/jpeg ";
// private static final String [] FontNames={ "SansSerif ", "Serif ", "MonoSpaced ", "Dialog ", "DialogInput "};

//Initialize global variables
public void init() throws ServletException {
}

//Process the HTTP Get request
public void doGet(HttpServletRequest request, HttpServletResponse response) throws
ServletException, IOException {
response.setContentType(CONTENT_TYPE);
response.setHeader( "Pragma ", "no-cache ");
response.setHeader( "Cache-Control ", "no-cache ");
response.setDateHeader( "Expires ", 0);

// 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.createGraphics();

//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( "DialogInput ", Font.ITALIC, 18));
// g.setFont(new Font(FontNames[random.nextInt(6)%5], Font.ITALIC, 18));
//画边框
//g.setColor(new Color());
//g.drawRect(0,0,width-1,height-1);

// 随机产生255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 < 255; 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 = " ";
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);
}
//System.out.println( "validate code= " + sRand);

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

// 图象生效
g.dispose();

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