定义一个 Servlet 用来在内存中生成 二维码图片，并向浏览器页面输出。
1 import javax.imageio.ImageIO;
2 import javax.servlet.ServletException;
3 import javax.servlet.annotation.WebServlet;
4 import javax.servlet.http.HttpServlet;
5 import javax.servlet.http.HttpServletRequest;
6 import javax.servlet.http.HttpServletResponse;
7 import java.awt.*;
8 import java.awt.image.BufferedImage;
9 import java.io.IOException;
10 import java.util.Random;
11
12 @WebServlet("/checkCodeServlet")
13 public class CheckCodeServlet extends HttpServlet {
14 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
15
16 // 定义图片的宽高
17 int width = 100;
18 int height = 50;
19
20 // 1 创建对象，在内存中生成图片（验证码图片对象）
21 BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_BGR);
22
23 // 2 修饰图片
24 // 2.1 填充背景色
25 Graphics g = image.getGraphics(); //获取画笔对象
26 g.setColor(Color.pink); // 设置画笔颜色
27 g.fillRect(0,0,width,height); // 绘制一个矩形，给定坐标与宽高
28
29 // 2.2 画边框
30 g.setColor(Color.blue); // 设置画笔颜色
31 g.drawRect(0,0,width-1,height-1); // 给图像绘制边框
32
33 String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghigklmnopqrstuvwxyz0123456789";
34 //生成随机角标
35 Random ran = new Random();
36
37 for (int i = 1; i <= 4; i++) {
38 int index = ran.nextInt(str.length());
39 //获取字符
40 char ch = str.charAt(index);//随机字符
41 //2.3写验证码
42 g.drawString(ch+"",width/5*i,height/2);
43 }
44
45 //2.4画干扰线
46 g.setColor(Color.GREEN);
47
48 // 随机生成坐标点
49
50 for (int i = 0; i < 6; i++) {
51 int x1 = ran.nextInt(width);
52 int x2 = ran.nextInt(width);
53
54 int y1 = ran.nextInt(height);
55 int y2 = ran.nextInt(height);
56 g.drawLine(x1,y1,x2,y2); // 画干扰线
57 }
58
59
60 // 3 将图片输出到页面展示：通过response 的 字符流，将图片输出到浏览器上
61 ImageIO.write(image,"jpg",response.getOutputStream());
62 }
63
64 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
65 this.doPost(request, response);
66 }
67 }
定义一个web页面，用来查看验证码，可以刷新验证码。
1 <!DOCTYPE html>
2 <html lang="en">
3 <head>
4 <meta charset="UTF-8">
5 <title>验证码</title>
6
7 <script>
8 /*
9 点击超链接或者图片，需要换一张
10 1.给超链接和图片绑定单击事件
11
12 2.重新设置图片的src属性值
13
14 */
15 window.onload = function(){
16 //1.获取图片对象
17 var img = document.getElementById("checkCode");
18 //2.绑定单击事件
19 img.onclick = function(){
20 //加时间戳
21 var date = new Date().getTime();
22
23 img.src = "/web/checkCodeServlet?"+date;
24 }
25
26 // 获取超链接对象
27 var a = document.getElementById("change");
28
29 a.onclick = img.onclick();
30
31 }
32
33
34 </script>
35
36
37 </head>
38 <body>
39
40
41 <img id="checkCode" src="/web/checkCodeServlet" />
42
43 <a id="change" href="javascript:;">看不清换一张？</a>
44
45 </body>
46 </html>
效果图
