验证码设计

package cn.it.web.controller;

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

public class ImageServlet extends HttpServlet {
 int width = 80;
 int height = 20;
 char[] buf = "0123456789abcdefghijkmnopqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ".toCharArray();

 @Override
 protected void doGet(HttpServletRequest req, HttpServletResponse resp)
   throws ServletException, IOException {
  BufferedImage image = new BufferedImage(width, height,
    BufferedImage.TYPE_INT_RGB);
  Graphics g = image.getGraphics();
  // 填充背景
  g.setColor(Color.WHITE);
  g.fillRect(0, 0, width, height);
  // 画框
  g.setColor(Color.BLACK);
  g.drawRect(0, 0, width - 1, height - 1);
  // 写字符
  g.setColor(Color.BLUE);
  g.setFont(new Font("粗体", Font.BOLD, 15));
  Random r = new Random();
  StringBuilder sb = new StringBuilder();
  for (int i = 0; i < 4; i++) {
   int pos = r.nextInt(buf.length);
   char c = buf[pos];
   sb.append(c);
   g.drawString(String.valueOf(c), (i * 2 + 1) * (width / 9), 15);
  }
  String code = sb.toString();
  // 将验证码存入session
  req.getSession().setAttribute("code", code);
  ImageIO.write(image, "jpeg", resp.getOutputStream());
 }

 @Override
 protected void doPost(HttpServletRequest req, HttpServletResponse resp)
   throws ServletException, IOException {
  doGet(req, resp);
 }
}