生成驗證碼的程序

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
import java.awt.*;
import java.awt.image.*;
import java.util.*;
import javax.imageio.*;
@WebServlet("/AuthServlet")
public class AuthServlet extends HttpServlet {
	public void doGet(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {
		String s = String.valueOf(new Random().nextInt(9000) + 1000);
		HttpSession session = request.getSession();
		session.setAttribute("auth", s);
		
		response.setContentType("image/jpeg");
		response.setHeader("Pragma", "no-cache");
		response.setHeader("Cache-control", "no-cache");
		response.setDateHeader("Expires",0);
		
		OutputStream os = response.getOutputStream();
		BufferedImage image = 
			new BufferedImage(38,20,BufferedImage.TYPE_INT_RGB);
		Graphics g = image.getGraphics();
		g.setColor(Color.LIGHT_GRAY);
		g.fillRect(0, 0, 38, 20);
		g.setColor(Color.BLUE);
		g.drawString(s, 6, 14);
		ImageIO.write(image, "JPEG", os);
		os.close();
	}
}

在jsp中加入

<img src="<%= request.getContextPath() + "/AuthServlet" %>" />