通常的登录注册系统都会要求输入验证码以区别用户行为和计算机程序行为来防止恶意注册、暴力破解密码等。

Jsp或者Java Web开发中通常用 Java 的 Graphics 绘制验证码图片然后用ImageIO输出为Jpg等格式的图片再通过Session来验证输入内容与验证码内容的一致性。

具体代码和步骤如下：

1.生成验证码的Servlet

 

1. Java 代码复制内容到剪贴板  
2.       
3. import java.io.IOException;            
4. import javax.servlet.ServletException;            
5. import javax.servlet.http.HttpServlet;            
6. import javax.servlet.http.HttpServletRequest;            
7. import javax.servlet.http.HttpServletResponse;            
8. import javax.servlet.http.HttpSession;            
9. import java.util.*;            
10. import java.awt.*;            
11. import java.awt.image.*;            
12.             
13. import javax.imageio.*;            
14. /**       
15. *         
16. * @author mzba       
17. *       
18. */          
19. public class GetCaptcha extends HttpServlet {            
20.     private static final long serialVersionUID = 1L;            
21.             
22.     /**         
23.      * @see HttpServlet#HttpServlet()         
24.      */            
25.     public GetCaptcha() {            
26.         super();            
27.         // TODO Auto-generated constructor stub            
28.     }            
29.             
30.     /**         
31.      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse         
32.      *      response)         
33.      */            
34.     protected void doGet(HttpServletRequest request,            
35.             HttpServletResponse response) throws ServletException, IOException {            
36.         response.setContentType("image/jpeg");            
37.         response.setHeader("Pragma", "No-cache");            
38.         response.setHeader("Cache-Control", "no-cache");            
39.         response.setDateHeader("Expires", 0);            
40.         HttpSession session = request.getSession();            
41.         // 在内存中创建图象            
42.         int width = 75, height = 25;            
43.         BufferedImage image = new BufferedImage(width, height,            
44.                 BufferedImage.TYPE_INT_RGB);            
45.         // 获取图形上下文            
46.         Graphics g = image.getGraphics();            
47.         // 生成随机类            
48.         Random random = new Random();            
49.         // 设定背景色            
50.         g.setColor(getRandColor(200, 250));            
51.         g.fillRect(0, 0, width, height);            
52.         // 设定字体            
53.         g.setFont(new Font("Times New Roman", Font.PLAIN, 24));            
54.         // 画边框            
55.         g.setColor(getRandColor(160, 200));            
56.         g.drawRect(0, 0, width - 1, height - 1);            
57.         // 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到            
58.         g.setColor(getRandColor(160, 200));            
59.         for (int i = 0; i < 155; i++) {            
60.             int x = random.nextInt(width);            
61.             int y = random.nextInt(height);            
62.             int xl = random.nextInt(12);            
63.             int yl = random.nextInt(12);            
64.             g.drawLine(x, y, x + xl, y + yl);            
65.         }            
66.         // 取随机产生的认证码(4位数字)            
67.         String sRand = "";            
68.         for (int i = 0; i < 4; i++) {            
69.             String rand = String.valueOf(random.nextInt(10));            
70.             sRand += rand;            
71.             // 将认证码显示到图象中            
72.             g.setColor(new Color(20 + random.nextInt(110), 20 + random            
73.                     .nextInt(110), 20 + random.nextInt(110)));            
74.             // 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成            
75.             g.drawString(rand, 13 * i + 14, 20);            
76.         }            
77.             
78.         // 将认证码存入SESSION            
79.         session.setAttribute("vcode", sRand);            
80.             
81.         // 图象生效            
82.         g.dispose();            
83.         // 输出图象到页面            
84.         ImageIO.write(image, "JPEG", response.getOutputStream());            
85.     }            
86.             
87.     /**         
88.      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse         
89.      *      response)         
90.      */            
91.     protected void doPost(HttpServletRequest request,            
92.             HttpServletResponse response) throws ServletException, IOException {            
93.         // TODO Auto-generated method stub            
94.     }            
95.             
96.     Color getRandColor(int fc, int bc) {// 给定范围获得随机颜色            
97.         Random random = new Random();            
98.         if (fc > 255)            
99.             fc = 255;            
100.         if (bc > 255)            
101.             bc = 255;            
102.         int r = fc + random.nextInt(bc - fc);            
103.         int g = fc + random.nextInt(bc - fc);            
104.         int b = fc + random.nextInt(bc - fc);            
105.         return new Color(r, g, b);            
106.     }            
107.             
108. }        

2.web.xml中添加上面Servlet的映射信息

 

1. XML/HTML 代码复制内容到剪贴板  
2.       
3. <servlet>            
4.    <description>用于生成验证码</description>            
5.    <display-name>生成验证码</display-name>            
6.    <servlet-name>GetCaptcha</servlet-name>            
7.    <servlet-class>servlets.GetCaptcha</servlet-class>            
8. </servlet>            
9.           
10. <servlet-mapping>            
11.   <servlet-name>GetCaptcha</servlet-name>            
12.   <url-pattern>/getcaptcha.sl</url-pattern>            
13. </servlet-mapping>    

3.在前台界面中调用此Servlet

 

1. XML/HTML 代码复制内容到剪贴板  
2.       
3. <img src="getcaptcha.sl" alt="验证码" name="checkImg" id="checkImg" style="position:relative; top:5px; left:20px; " onClick="document.getElementById('checkImg').src='getcaptcha.sl?temp='+ (new Date().getTime().toString(36)); return false"/>        

 

     本文转自06peng 51CTO博客，原文链接：http://blog.51cto.com/06peng/962391，如需转载请自行联系原作者