JavaWeb学习day6-Response初学2（生成随机数验证码）

 1 public class imageServlet extends HttpServlet {
 2     @Override
 3     protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
 4         resp.setHeader("refresh", "3");//3秒自动刷新
 5
 6         BufferedImage image = new BufferedImage(90, 30, BufferedImage.TYPE_INT_RGB);//创建图片
 7
 8         Graphics2D g = (Graphics2D) image.getGraphics();//笔
 9
10         g.setColor(Color.WHITE);//设置背景颜色
11         g.fillRect(0, 0, 90, 30);
12
13         g.setColor(Color.blue);
14         g.setFont(new Font(null, Font.BOLD, 20));
15         g.drawString(f(), 0, 20);
16
17         resp.setContentType("image/jpg");//让浏览器以图片形式打开
18         resp.setDateHeader("expires", -1);//不让浏览器缓存；作用：不论是刷新网页或者如何，都会显示最新的内容
19         resp.setHeader("Cache-Control", "no-cache");
20         resp.setHeader("pragma", "no-cache");
21
22         ImageIO.write(image, "jpg", resp.getOutputStream());//把图片写给浏览器
23
24     }
25
26     private String f() {
27         Random random = new Random();
28         String s = random.nextInt(99999999) + "";
29
30         StringBuffer stringBuffer = new StringBuffer();
31         for (int i = 0; i < 8 - s.length(); i++) {
32             stringBuffer.append("0");//保证序列位数
33         }
34         String s1 = stringBuffer.toString() + s;
35         return s1;
36     }