生成验证码

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.security.SecureRandom;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

@SuppressWarnings("serial")
public class ValidateCodeServlet extends HttpServlet
{
    private static Log logger = LogFactory.getLog(ValidateCodeServlet.class);

    private static final String CONTENT_TYPE = "image/jpeg";

    private static final int WIDTH = 64;

    private static final int HEIGHT = 22;

    private static final char[] PARAM = {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e',
        'f', 'g', 'h', 'i', 'j', 'k', 'L', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'A',
        'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W',
        'X', 'Y', 'Z'};

    public ValidateCodeServlet()
    {
        super();
    }

    public void destroy()
    {
        super.destroy();
    }

    public void doGet(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException
    {
        doPost(request, response);
    }

    public void doPost(HttpServletRequest request, HttpServletResponse response)
        throws ServletException, IOException
    {
        response.setContentType(CONTENT_TYPE);

        try
        {
            SecureRandom ran = new SecureRandom();
            StringBuilder sb = new StringBuilder();

            // 产生验证码
            for (int i = 0; i < 4; i++)
            {
                char temp = PARAM[Math.abs((ran.nextInt()) % 62)];
                while (sb.indexOf(String.valueOf(temp)) != -1)
                {
                    temp = PARAM[Math.abs((ran.nextInt()) % 62)];
                }
                sb.append(temp).append("");
            }

            // 将验证码保存到Session中
            request.getSession().setAttribute(TUSConstant.SESSION_VERIFICODE, sb.toString());

            // 输出图片到页面
            BufferedImage image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);
            Graphics2D g = (Graphics2D)image.getGraphics();
            g.setColor(new Color(255, 255, 255));
            g.fillRect(0, 0, WIDTH, HEIGHT);

            for (int i = 0; i < 18; i++)
            {
                g.setColor(new Color(ran.nextInt(100) + 110, ran.nextInt(100) + 110, ran.nextInt(100) + 110));
                int x_b = ran.nextInt(WIDTH);
                int x_e = ran.nextInt(WIDTH);
                int y_b = ran.nextInt(HEIGHT + 1);
                int y_e = ran.nextInt(HEIGHT + 1);
                g.drawLine(x_b, y_b, x_e, y_e);
            }

            g.setFont(new Font("System", Font.BOLD, 18));
            // g.setColor(new Color(0, 0, 255));
            g.setColor(new Color(ran.nextInt(100) + 110, ran.nextInt(100) + 110, ran.nextInt(100) + 110));
            g.drawString(sb.toString(), 5, 15);
            g.dispose();
            JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(response.getOutputStream());
            encoder.encode(image);
        }
        catch (Exception ex)
        {
            logger.error("doPost error.", ex);
        }
    }
}