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[Java教程]java web 实现验证码

验证码的作用:通常的登录或者注册系统时,都会要求用户输入验证码,以此区别用户行为和计算机程序行为,目的是有人防止恶意注册、暴力破解密码等。

实现验证码的思路:用 server 实现随机生成数字和字母组成图片的功能,用 jsp 页面实现显示验证码和用户输入验证码的功能,再用 server 类分别获取图片和用户输入的数据,判断两个数据是否一致。

代码实现

1.编写数字、英文随机生成的 server 类,源码:

 1 package com; 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.ByteArrayOutputStream; 8 import java.io.IOException; 9 import java.io.PrintWriter; 10  11 import javax.imageio.ImageIO; 12 import javax.servlet.ServletException; 13 import javax.servlet.ServletOutputStream; 14 import javax.servlet.http.HttpServlet; 15 import javax.servlet.http.HttpServletRequest; 16 import javax.servlet.http.HttpServletResponse; 17 import javax.servlet.http.HttpSession; 18  19 public class logcheck extends HttpServlet { 20  21   public logcheck() { 22     super(); 23   } 24  25    26   public void destroy() { 27     super.destroy();  28   } 29  30   public void doGet(HttpServletRequest request, HttpServletResponse response) 31       throws ServletException, IOException { 32  33     doPost(request, response); 34   } 35  36  37   /*实现的核心代码*/ 38   public void doPost(HttpServletRequest request, HttpServletResponse response) 39       throws ServletException, IOException { 40  41     response.setContentType("image/jpeg"); 42     HttpSession session=request.getSession(); 43     int width=60; 44     int height=20; 45      46     //设置浏览器不要缓存此图片 47     response.setHeader("Pragma", "No-cache"); 48     response.setHeader("Cache-Control", "no-cache"); 49     response.setDateHeader("Expires", 0); 50      51     //创建内存图像并获得图形上下文 52     BufferedImage image=new BufferedImage(width, height,BufferedImage.TYPE_INT_RGB); 53     Graphics g=image.getGraphics(); 54      55     /* 56      * 产生随机验证码 57      * 定义验证码的字符表 58     */ 59     String chars="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"; 60     char[] rands=new char[4]; 61     for(int i=0;i<4;i++){ 62       int rand=(int) (Math.random() *36); 63       rands[i]=chars.charAt(rand); 64     } 65      66     /* 67      * 产生图像 68      * 画背景 69     */ 70     g.setColor(new Color(0xDCDCDC)); 71     g.fillRect(0, 0, width, height); 72      73     /* 74      * 随机产生120个干扰点 75     */ 76      77     for(int i=0;i<120;i++){ 78       int x=(int)(Math.random()*width); 79       int y=(int)(Math.random()*height); 80       int red=(int)(Math.random()*255); 81       int green=(int)(Math.random()*255); 82       int blue=(int)(Math.random()*255); 83       g.setColor(new Color(red,green,blue)); 84       g.drawOval(x, y, 1, 0); 85     } 86     g.setColor(Color.BLACK); 87     g.setFont(new Font(null, Font.ITALIC|Font.BOLD,18)); 88      89     //在不同高度输出验证码的不同字符 90     g.drawString(""+rands[0], 1, 17); 91     g.drawString(""+rands[1], 16, 15); 92     g.drawString(""+rands[2], 31, 18); 93     g.drawString(""+rands[3], 46, 16); 94     g.dispose(); 95      96     //将图像传到客户端 97     ServletOutputStream sos=response.getOutputStream(); 98     ByteArrayOutputStream baos=new ByteArrayOutputStream(); 99     ImageIO.write(image, "JPEG", baos);100     byte[] buffer=baos.toByteArray();101     response.setContentLength(buffer.length);102     sos.write(buffer);103     baos.close();104     sos.close();105     106     session.setAttribute("checkcode", new String(rands));107   }108 109   110   public void init() throws ServletException {111     // Put your code here112   }113 114 }

 

2.用于显示验证码的页面:

 1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> 2 <% 3 String path = request.getContextPath(); 4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; 5 %> 6  7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 8 <html> 9  <head>10   <base href="<%=basePath%>">11   12   <title>index</title>13   <meta http-equiv="pragma" content="no-cache">14   <meta http-equiv="cache-control" content="no-cache">15   <meta http-equiv="expires" content="0">  16   <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">17   <meta http-equiv="description" content="This is my page">18   <!--19   <link rel="stylesheet" type="text/css" href="styles.css">20   -->21  </head>22  23  <body>24  <form action="yanzheng" method="post">25    <input type="text" name="name" size="5" maxlength="4">26   <a href="index.jsp"><img border="0" src="logcheck"></a><br><br>27   &nbsp&nbsp&nbsp&nbsp&nbsp<input type="submit" value="提交">28  </form>29  </body>30 </html>

 

3.用于检验输入的验证码是否正确:

 1 package com; 2  3 import java.io.IOException; 4 import java.io.PrintWriter; 5  6 import javax.jms.Session; 7 import javax.servlet.ServletException; 8 import javax.servlet.http.HttpServlet; 9 import javax.servlet.http.HttpServletRequest;10 import javax.servlet.http.HttpServletResponse;11 import javax.servlet.http.HttpSession;12 13 public class yanzheng extends HttpServlet {14 15   public yanzheng() {16     super();17   }18 19   public void destroy() {20     super.destroy(); 21   }22 23   public void doGet(HttpServletRequest request, HttpServletResponse response)24       throws ServletException, IOException {25 26     doPost(request, response);27   }28   /*核心代码*/29   public void doPost(HttpServletRequest request, HttpServletResponse response)30       throws ServletException, IOException {31 32     String info=null;33     /*获取输入的值*/34     String value1=request.getParameter("name");35 36     /*获取图片的值*/37     HttpSession session=request.getSession();38     String value2=(String)session.getAttribute("checkcode");39 40     /*对比两个值(字母不区分大小写)*/41     if(value2.equalsIgnoreCase(value1)){42       info="验证码输入正确";43     }else{44       info="验证码输入错误";45     }46     System.out.println(info);47     request.setAttribute("info", info);48     request.getRequestDispatcher("/login.jsp").forward(request, response);49   }50 51   52   public void init() throws ServletException {53     // Put your code here54   }55 56 }

 

4.显示输入结构界面(输入验证码是否正确):

 1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> 2 <% 3 String path = request.getContextPath(); 4 String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; 5 %> 6  7 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 8 <html> 9  <head>10   <base href="<%=basePath%>">11   12   <title>My JSP 'login.jsp' starting page</title>13   14   <meta http-equiv="pragma" content="no-cache">15   <meta http-equiv="cache-control" content="no-cache">16   <meta http-equiv="expires" content="0">  17   <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">18   <meta http-equiv="description" content="This is my page">19   <!--20   <link rel="stylesheet" type="text/css" href="styles.css">21   -->22 23  </head>24  25  <body>26   <%=request.getAttribute("info") %>27  </body>28 </html>

5.项目结构、效果截图: