登录页面中的那个验证码怎么编码啊，是个按钮吗？如果不是，那是什么啊？

import java.awt.image.BufferedImage;
import import import import java.util.HashMap;
import java.util.Map;
import java.util.Random;
import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;
public class ImageUtils {
    private static String str = "1234567890QWERTYUIOPASDFGHJKLZXCVBNM";
    private static char[] chars = str.toCharArray();
    private static int WIDTH = 140;
    private static int HEIGHT = 40;
    private static int SIZE = 4;
    private static int LINES = 6;
    private static int FONT_SIZE = 40;
    public static Map<String, BufferedImage> getImage() {
        BufferedImage image = new BufferedImage(WIDTH, HEIGHT,
                BufferedImage.TYPE_INT_RGB);
        Graphics g = image.createGraphics();
        g.setColor(Color.GRAY);
        g.fillRect(0, 0, WIDTH, HEIGHT);
        StringBuffer bf = new StringBuffer();
        Random r = new Random();
        for (int i = 0; i < SIZE; i++) {
            char c = chars[r.nextInt(chars.length)];
            g.setColor(getColor());
            g.setFont(new Font(null,Font.BOLD,FONT_SIZE));
            g.drawString("" + c, i * WIDTH / SIZE, HEIGHT / 10 * 9);
            bf.append(c);
        }
        for (int i = 0; i < LINES; i++) {
            g.setColor(getColor());
            g.drawLine(r.nextInt(WIDTH), r.nextInt(HEIGHT), r.nextInt(WIDTH), r.nextInt(HEIGHT));
        }
        Map<String, BufferedImage> map = new HashMap<String, BufferedImage>();
        map.put(bf.toString(), image);
        return map;
    }
    private static Color getColor() {
        Random r = new Random();
        return new Color(r.nextInt(255), r.nextInt(255), r.nextInt(255));
    }

    public static InputStream imageToStream(BufferedImage image) throws Exception{
        ByteArrayOutputStream bos = new ByteArrayOutputStream();
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(bos);
        encoder.encode(image);
        byte[] bytes = bos.toByteArray();
        InputStream is = new ByteArrayInputStream(bytes);
        return is;
    }
}

这段代码能可以生成验证码，希望可以帮你

import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;
我想问一下上面的两个包是啥意思，谢谢

Sun开发的Java版本的JPEG编码、解码类库