为登录添加验证码

主要用到知识：1.Servlet　　2.request从客户端得到参数　　3.response向客户端响应

　　　　　　4.字符编码解决乱码问题　　　　5.jsp的使用　　6.验证码

　　　　　　7.Cookie的使用　　　　　　8.Session的使用　　9.具体功能登录时自动补全用户名

　　　　　　10.jsp页面的用户信息校验，如果为null，则跳转登录。

////使用一个VerifyCodeServlet专门来生成验证码

login.jsp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>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     <script type="text/javascript">
24         function _change(){
25             //1.得到img元素
26             //2.修改其src为/XJS_Session/VerifyCodeServlet
27             var imgEle=document.getElementById("img");
28             //有缓冲，加参数---时间
29             imgEle.src="/XJS_Session/VerifyCodeServlet?a="+new Date().getTime();
30         }
31     </script>
32   </head>
33   
34   <body>
35     <h1>登录</h1>
36     <%
37         String uname="";
38         //读名为username的cookie
39         Cookie[] cookies=request.getCookies();
40         if(cookies!=null){
41             for(Cookie c:cookies){
42                 //如果为空显示：""
43                 //如果不为显示：Cookie值
44                 if("username".equals(c.getName())){
45                     uname=c.getValue();
46                 }
47             }
48         }
49      %>
50     
51     <%
52         String message="";//一个空字符串
53         String msg=(String)request.getAttribute("msg");//获取错误信息
54         if(msg!=null){
55             message=msg;
56         }
57      %>
58     <font color="red"><b><%=message %></b></font>
59     <form action="/XJS_Session/LoginServlet" method="post">
60         用户名：<input type="text" name="username" value="<%=uname %>"><br>
61         密&nbsp;&nbsp;&nbsp;码：<input type="password" name="password"><br>
62         验证码：<input type="text" name="verifyCode" size="7">
63                 <img id="img" src="/XJS_Session/VerifyCodeServlet"><br>
64                 <a href="javascript:_change()">看不清，换一张</a>
65         <input type="submit" value="提交">
66     </form>
67   </body>
68 </html>

LoginServlet.java:

 1 public class LoginServlet extends HttpServlet {
 2 
 3     public void doPost(HttpServletRequest request, HttpServletResponse response)
 4             throws ServletException, IOException {
 5             /*
 6              * 校验验证码
 7              * 1.从session中获取正确的验证码
 8              * 2.从表单中获取用户输入的验证码
 9              * 4.如果相同，向下运行，否则保存错误信息到request域，转发到login.jsp
10              */
11             HttpSession session1 = request.getSession();
12             String vcode1 = (String) session1.getAttribute("session_vcode");
13             String vcode2 = request.getParameter("verifyCode");
14             System.out.println("1:"+vcode1+" 2:"+vcode2);
15             if(!vcode1.equalsIgnoreCase(vcode2)){//不相等----不区分大小写
16                 request.setAttribute("msg", "验证码错误！");
17                 RequestDispatcher rd=request.getRequestDispatcher("/login.jsp");
18                 rd.forward(request, response);
19                 return;//错误结束，就不向下执行
20             }
21                 
22             
23             
24             
25             request.setCharacterEncoding("utf-8");
26             String username = request.getParameter("username");
27             String password = request.getParameter("password");
28             System.out.println("username:"+username+", password:"+password);
29             if(username!="" && password!=""){
30                 if("xjs".equals(username) && "0309".equals(password)){
31                     //设置Cookie
32                     response.setContentType("text/html;charset=utf-8");
33                     Cookie cookie=new Cookie("username",username);
34                     cookie.setMaxAge(60*60);
35                     response.addCookie(cookie);//把它显示到用户名文本框中
36                     
37                     
38                     //登录成功
39                     HttpSession session=session1;
40                     session.setAttribute("username", username);
41                     session.setAttribute("password", password);
42                     //重定向到succ1.jsp
43                     response.sendRedirect("/XJS_Session/succ1.jsp");
44                 }
45                     else{
46                     System.out.println("username:"+username+", password:"+password);
47                     //输入的用户名和密码不存在
48                     request.setAttribute("msg", "用户名和密码不存在！！！");
49                     //用转发
50                     RequestDispatcher rd=request.getRequestDispatcher("/login.jsp");
51                     rd.forward(request, response);
52                 }
53             }else{
54                 request.setAttribute("msg", "用户名或密码不能为空！！！");
55                 //用转发---如果用重定向的话显示错误信息就不能使用request
56                 RequestDispatcher rd=request.getRequestDispatcher("/login.jsp");
57                 rd.forward(request, response);
58             }
59     }
60 }

=============================验证码===========================

VerifyCode.java:

  1 package com.xjs.commons;
  2 
  3 import java.awt.BasicStroke;
  4 import java.awt.Color;
  5 import java.awt.Font;
  6 import java.awt.Graphics2D;
  7 import java.awt.image.BufferedImage;
  8 import java.io.IOException;
  9 import java.io.OutputStream;
 10 import java.util.Random;
 11 
 12 import javax.imageio.ImageIO;
 13 
 14 public class VerifyCode {
 15     private int w = 70;
 16     private int h = 35;
 17      private Random r = new Random();
 18      // {"宋体", "华文楷体", "黑体", "华文新魏", "华文隶书", "微软雅黑", "楷体_GB2312"}
 19     private String[] fontNames  = {"宋体", "华文楷体", "黑体", "微软雅黑", "楷体_GB2312"};
 20     // 可选字符
 21     private String codes  = "23456789abcdefghjkmnopqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ";
 22     // 背景色
 23     private Color bgColor  = new Color(255, 255, 255);
 24     // 验证码上的文本
 25     private String text ;
 26     
 27     // 生成随机的颜色
 28     private Color randomColor () {
 29         int red = r.nextInt(150);
 30         int green = r.nextInt(150);
 31         int blue = r.nextInt(150);
 32         return new Color(red, green, blue);
 33     }
 34     
 35     // 生成随机的字体
 36     private Font randomFont () {
 37         int index = r.nextInt(fontNames.length);
 38         String fontName = fontNames[index];//生成随机的字体名称
 39         int style = r.nextInt(4);//生成随机的样式, 0(无样式), 1(粗体), 2(斜体), 3(粗体+斜体)
 40         int size = r.nextInt(5) + 24; //生成随机字号, 24 ~ 28
 41         return new Font(fontName, style, size);
 42     }
 43     
 44     // 画干扰线
 45     private void drawLine (BufferedImage image) {
 46         int num  = 3;//一共画3条
 47         Graphics2D g2 = (Graphics2D)image.getGraphics();
 48         for(int i = 0; i < num; i++) {//生成两个点的坐标，即4个值
 49             int x1 = r.nextInt(w);
 50             int y1 = r.nextInt(h);
 51             int x2 = r.nextInt(w);
 52             int y2 = r.nextInt(h); 
 53             g2.setStroke(new BasicStroke(1.5F)); 
 54             g2.setColor(Color.BLUE); //干扰线是蓝色
 55             g2.drawLine(x1, y1, x2, y2);//画线
 56         }
 57     }
 58     
 59     // 随机生成一个字符
 60     private char randomChar () {
 61         int index = r.nextInt(codes.length());
 62         return codes.charAt(index);
 63     }
 64     
 65     // 创建BufferedImage
 66     private BufferedImage createImage () {
 67         BufferedImage image = new BufferedImage(w, h, BufferedImage.TYPE_INT_RGB); 
 68         Graphics2D g2 = (Graphics2D)image.getGraphics(); 
 69         g2.setColor(this.bgColor);
 70         g2.fillRect(0, 0, w, h);
 71          return image;
 72     }
 73     
 74     // 调用这个方法得到验证码
 75     public BufferedImage getImage () {
 76         BufferedImage image = createImage();//创建图片缓冲区 
 77         Graphics2D g2 = (Graphics2D)image.getGraphics();//得到绘制环境
 78         StringBuilder sb = new StringBuilder();//用来装载生成的验证码文本
 79         // 向图片中画4个字符
 80         for(int i = 0; i < 4; i++)  {//循环四次，每次生成一个字符
 81             String s = randomChar() + "";//随机生成一个字母 
 82             sb.append(s); //把字母添加到sb中
 83             float x = i * 1.0F * w / 4; //设置当前字符的x轴坐标
 84             g2.setFont(randomFont()); //设置随机字体
 85             g2.setColor(randomColor()); //设置随机颜色
 86             g2.drawString(s, x, h-5); //画图
 87         }
 88         this.text = sb.toString(); //把生成的字符串赋给了this.text
 89         drawLine(image); //添加干扰线
 90         return image;        
 91     }
 92     
 93     // 返回验证码图片上的文本
 94     public String getText () {
 95         return text;
 96     }
 97     
 98     // 保存图片到指定的输出流
 99     public static void output (BufferedImage image, OutputStream out) 
100                 throws IOException {
101         ImageIO.write(image, "JPEG", out);
102     }
103 }

VerifyCodeServlet.java:

 1 import java.awt.image.BufferedImage;
 2 import java.io.IOException;
 3 import java.io.PrintWriter;
 4 
 5 import javax.servlet.ServletException;
 6 import javax.servlet.http.HttpServlet;
 7 import javax.servlet.http.HttpServletRequest;
 8 import javax.servlet.http.HttpServletResponse;
 9 
10 import com.xjs.commons.VerifyCode;
11 
12 public class VerifyCodeServlet extends HttpServlet {
13 
14     public void doGet(HttpServletRequest request, HttpServletResponse response)
15             throws ServletException, IOException {
16         /**
17          * 1.生成图片
18          * 2.保存图片上的文本到session中
19          * 3.把图片响应到客户端
20          */
21         VerifyCode vc=new VerifyCode();
22         BufferedImage bi=vc.getImage();
23         request.getSession().setAttribute("session_vcode", vc.getText());
24         //参数输出流，ServletOutputStream  getOutputStream();返回输入流---跟getWriter()方法不能同时使用，跟JavaSE中的输出流类似
25         VerifyCode.output(bi, response.getOutputStream());
26     }
27 }

 ////////////////////

succ1.jsp和succ2.jsp：

 1   <body>
 2    <%
 3        
 4            if(session.getAttribute("username")==null&&session.getAttribute("password")==null){
 5                //重定向到login.jsp
 6                response.sendRedirect("/XJS_Session/login.jsp");
 7                return;//别的就不执行了
 8            }
 9     %>
10     <%
11         String username=(String)session.getAttribute("username");
12         String password=(String)session.getAttribute("password");
13         out.print("用户名："+username);
14         out.print("密码："+password);
15         
16      %>
17   </body>
【推广】 免费学中医，健康全家人
原文地址：https://www.cnblogs.com/xjs1874704478/p/10850116.html