servlet生成验证码

package servlet;

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

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

public class ImgServlet extends HttpServlet {

	/**
	 * Constructor of the object.
	 */
	public ImgServlet() {
		super();
	}

	/**
	 * The doGet method of the servlet. <br>
	 *
	 * This method is called when a form has its tag value method equals to get.
	 * 
	 * @param request the request send by the client to the server
	 * @param response the response send by the server to the client
	 * @throws ServletException if an error occurred
	 * @throws IOException if an error occurred
	 */
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		response.setContentType("image/jpeg");
		response.setHeader("Pragma", "No-cache");
		response.setHeader("Cache-Control", "no-cache");
		response.setDateHeader("Expires", 0);
		OutputStream out=response.getOutputStream();
		int width=80,height=20;
		BufferedImage image=new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
		Graphics g=image.getGraphics();
		Random random=new Random();
		g.setColor(Color.gray);
		g.fillRect(0, 0, width, height);
		g.setFont(new Font("Times New Roman",Font.ITALIC,18));
		String sRand="";
		for(int i=0;i<4;i++){
			String rand=String.valueOf(random.nextInt(10));
			sRand +=rand;
			g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));
			g.drawString(rand,20*i+6, 16);
		}
		HttpSession session=request.getSession();
		session.setAttribute("Verification-code", sRand);
		g.dispose();
		ImageIO.write(image, "JPEG", out);
	}

	/**
	 * The doPost method of the servlet. <br>
	 *
	 * This method is called when a form has its tag value method equals to post.
	 * 
	 * @param request the request send by the client to the server
	 * @param response the response send by the server to the client
	 * @throws ServletException if an error occurred
	 * @throws IOException if an error occurred
	 */
	public void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		doGet(request, response);
	}

}