response小结（三）—输出随机图片（验证码功能实现）

本文是一个很简单的向网页上输出验证码的实现喲！通过注释解释清楚了每一步！

Myeclipse下的Package Explorer显示文件结构如下：

ResponseDemo.java实现了输出随机图片的功能：

 1 package com.yyz.response;
 2 
 3 import java.awt.Color;
 4 import java.awt.Font;
 5 import java.awt.Graphics;
 6 import java.awt.image.BufferedImage;
 7 import java.io.IOException;
 8 import java.util.Random;
 9 
10 import javax.imageio.ImageIO;
11 import javax.servlet.ServletException;
12 import javax.servlet.http.HttpServlet;
13 import javax.servlet.http.HttpServletRequest;
14 import javax.servlet.http.HttpServletResponse;
15 //输出随机图片
16 public class ResponseDemo extends HttpServlet {
17 
18     public void doGet(HttpServletRequest request, HttpServletResponse response)
19             throws ServletException, IOException {
20         //6.设置头，控制浏览器不要缓存图片数据
21         response.setHeader("Expires", "-1");
22         response.setHeader("Cache-Control", "no-cache");
23         response.setHeader("Pragma", "no-cache");
24         
25         //5.通知浏览器以图片方式打开
26         response.setHeader("Content-type", "image/jpeg");
27         //1.在内存中创建一副图片
28         BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
29         //2.得到图片
30         Graphics g = image.getGraphics();
31         //修改图片背景色
32         g.setColor(Color.WHITE);
33         g.fillRect(0, 0,80, 20);
34         //3.向图片上写数据
35         g.setColor(Color.BLUE);
36         g.setFont(new Font(null,Font.BOLD,20));
37         g.drawString(nakeNum(), 0, 20);
38         //随机画出9条干扰线
39          Random rand = new Random();
40         for(int i = 0;i<9;i++){
41             g.setColor(Color.BLACK);
42             int x1 = rand.nextInt(80);
43             int y1 = rand.nextInt(20);
44             int x2 = rand.nextInt(80);
45             int y2 = rand.nextInt(20);
46             g.drawLine(x1, y1, x2, y2);
47         }
48         //4.将图片写给浏览器
49         ImageIO.write(image, "jpeg", response.getOutputStream());
50         
51 }
52 
53     private String nakeNum() {
54        Random r = new Random();
55        String num = r.nextInt(9999999)+"";//产生0-9999999的数字，但有可能不足7位，如123
56        StringBuffer sb = new StringBuffer();
57        for(int i = 0;i<7-num.length();i++){
58            sb.append("0");
59        }
60        return sb.toString()+num;
61     }
62 
63     public void doPost(HttpServletRequest request, HttpServletResponse response)
64             throws ServletException, IOException {
65            doGet(request,response);
66     }
67 }

 1 <!DOCTYPE html>
 2 <html>
 3   <head>
 4     <title>register.html</title>
 5       <meta name="keywords" content="keyword1,keyword2,keyword3">
 6     <meta name="description" content="this is my page">
 7     <meta name="content-type" content="text/html; charset=UTF-8">
 8     </head>
 9   <body>
10 <form action="">
11     用户名：<input type="text" name="username">
12     密码：<input type="password" name="password">
13     认证码：<input type="text" name="checkcode"><img src="/day06/servlet/ResponseDemo">
14     <input type="submit " value="注册">   <br>
15  <br>
16   </body>
17 </html>

最后附上测试结果：

输出随机图片时，图片上若想要输出中文，可以用一个字符数组存储多个汉字（直接存汉字的编码也行），然后用Random产生的随机数做下标取出对应中文，再产生要写上图片的字符串即可。