实现动态验证码

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

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

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



public class AuthCodeServlet extends HttpServlet {
	private static final long serialVersionUID = 1L;
	private static final int W = 60;
	private static final int H = 25;
	private static final String[] CTable = ("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").split(" ");
	
	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws ServletException, IOException {
		BufferedImage img = new BufferedImage(W, H, BufferedImage.TYPE_INT_RGB);
		Graphics g = img.getGraphics();
		
		// 画背景
		g.setColor(Color.PINK);
		g.fillRect(0, 0, img.getWidth(), img.getHeight());
		
		// 画干扰线
		g.setColor(Color.GRAY);
		for (int i = 0; i < 20; i++) {
			g.drawLine(new Random().nextInt(W), new Random().nextInt(H), 
					new Random().nextInt(W), new Random().nextInt(H));
		}
		
		// 随机生成四个数
		g.setColor(Color.BLUE);
		g.setFont(new Font("Courier New", Font.BOLD, 16));
		for (int i = 0; i < 4; i++) {
			g.drawString(CTable[new Random().nextInt(35)], 6 + i * 13, 17);
		}
		
		// 向客户端输出
		resp.setContentType("image/jpeg");
		JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(resp.getOutputStream());
		encoder.encode(img);
	}
	
}