简单验证码实现[servlet]

package leo.servlet;

import java.awt.Color;

import java.awt.Font;

import java.awt.Graphics2D;

import java.awt.image.BufferedImage;

import java.io.IOException;

import java.util.Random;

import javax.servlet.ServletException;

import javax.servlet.ServletOutputStream;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import javax.swing.text.Position.Bias;

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

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

/**

 * Servlet implementation class CheckCodeServlet

 */

@WebServlet("/CheckCodeServlet")

public class CheckCodeServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
public static final char[] CHARS = {'2','3','4','A','B','C','D','E'};
public static Random random = new Random();

private static String getRandomString() {
StringBuffer buffer = new StringBuffer();
for(int i=0; i<6; i++){
buffer.append(CHARS[random.nextInt(CHARS.length)]);
}
return buffer.toString();
}

public static Color getRandomColor() {
return new Color(random.nextInt(255), random.nextInt(255), random.nextInt(255));
}

public static Color getReverseColor(Color color) {
return new Color(255 - color.getRed(), 255 - color.getGreen(), 255 - color.getBlue());
}
  

    /**

     * @see HttpServlet#HttpServlet()

     */

    public CheckCodeServlet() {

        super();

        // TODO Auto-generated constructor stub

    }

/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("image/jpeg");
String randomString = getRandomString();
request.getSession(true).setAttribute("randomString", randomString);

int width = 100;
int height = 30;

Color color = getRandomColor();
Color reverseColor = getReverseColor(color);

BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_BGR);
Graphics2D graphics2d  = image.createGraphics();
graphics2d.setFont(new Font(Font.SANS_SERIF, Font.BOLD, 16));
graphics2d.setColor(color);
graphics2d.fillRect(0, 0, width, height);
graphics2d.setColor(reverseColor);
graphics2d.drawString(randomString, 18, 20);
for(int i=0, n=random.nextInt(100); i<n; i++){
graphics2d.drawRect(random.nextInt(width), random.nextInt(height), 1, 1);
}
ServletOutputStream outputStream = response.getOutputStream();
JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(outputStream);
encoder.encode(image);
outputStream.flush();

}

/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
doGet(request, response);
}

}

效果如下图：