Java后端开发——实现登录验证程序-编程知识

一、实现一个简单登录验证程序

实现一个简单的用户登录验证程序，如果用户名是 abc ，密码是 123，则显示欢迎用户的信息，否则显示“用户名或密码不正确”。

【分析】该案例采用 JSP 页面只完成提交信息和验证结果的显示，而验证过程由 Servlet 完成，这些组件通过 request （或 HttpServletRequest）对象实现数据共享。由提交页面将数据传递给 Servlet，而 Servlet 获取数据并实现验证，根据验证结果，转向显示验证结果的页面。

【设计】根据分析，该系统需要设计3个组件以及修改 web.xml 文件。

（1）登录表单页面： login.jsp。

（2）处理登录请求并实现验证的 Servlet：LoginCheckServlet.java。

（3）显示提示的页面： Info.jsp。

（4）修改 web.xml，配置 Servlet的信息。

假设，表单传递的参数为 username 和 userpwd。

1.登录表单页面login.jsp：

<%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>登录页面</title>
</head>
<body>
<form action="CheckServlet" method="post"><table><tr align="center"><td>请输入用户名：<input type="text" name="username" size="20"></td></tr><tr align="center"><td>请输入密码：&nbsp;&nbsp;<input type="password" name="userpwd"size="20"></td></tr align="center"><td><input type="submit" value="登录" /> <input type="reset" /></td></tr></table>
</form>
</body>
</html>

2.处理登录的 Servlet：LoginCheckServlet.java

package servlet;import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;public class LoginCheckServlet extends HttpServlet {private static final long serialVersionUID = 1L;protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {String userName = request.getParameter("username");String userPwd = request.getParameter("userpwd");String info = "";if(("abc".equals(userName))&&"123".equals(userPwd)){info = "欢迎你"+userName+"！";}else{info = "用户名或密码不正确！";}request.setAttribute("outputMessage", info);request.getRequestDispatcher("/info.jsp").forward(request,response);}
}

3.显示提示的页面 info.jsp：

<%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>Insert title here</title>
</head>
<body>
<%=request.getAttribute("outputMessage") %>
</body>
</html>

4.修改配置文件，在 web.xml 中，修改LoginCheckServlet 的配置信息：

在这里插入图片描述
注意:与前面的表单action路径一致

5.运行效果图

输入正确的用户名和密码

输入错误的用户名和密码

二、实现一个带验证码登录验证程序

1.前端的登陆页面如下：login.jsp

<%@ page language="java" contentType="text/html; charset=UTF-8"pageEncoding="UTF-8"%>
<html>
<head><title>Title</title>
</head>
<body><form action="login" method="post">姓名：<input name="name" type="text"><br><br>密码：<input name="password" type="password"><br><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<input name="vericode" placeholder="验证码" value="" style="width: 60px">&nbsp;&nbsp;<img id="vericodeImg" src="imageCode">&nbsp;&nbsp;<a id="kanbuq" href="javascript:changeImg();">看不清，换一张</a><br><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<input type="submit" value="提交"></form><script src="https://code.jquery.com/jquery-3.4.1.min.js"></script><script type="text/javascript">function changeImg() {//需要让每次请求的url都发生变化。否则服务器会认为访问的时一张图片，就不会刷新请求了//每次url一样，服务器会认为访问的url是同一张图片，没变化啊$("#vericodeImg").attr("src","imageCode?"+Math.random())}</script>
</body>
</html>

2.后端的LoginServlet登陆实现逻辑如下：LoginServlet.java

映射的url-patten: /login

package servlet;import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import java.io.IOException;public class LoginServlet extends HttpServlet {private static final long serialVersionUID = 1L;protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {response.setContentType("text/html;charset=utf8");String name=request.getParameter("name");String password=request.getParameter("password");String vericode=request.getParameter("vericode");String generatedCode= (String) request.getSession().getAttribute("verityCode");if (name.equals("bob")&&password.equals("123")&&vericode.toLowerCase().equals(generatedCode.toLowerCase())){response.getWriter().write("登录成功");}else {response.getWriter().write("登录失败");}}}

3.下面是两个工具代码：生成验证码字符串CreateVerificationCode.java

package bean;import java.util.Arrays;public class CreateVerificationCode {/*** 验证码难度级别*/public enum SecurityCodeLevel {Simple,Medium,Hard}public static String getSecurityCode() {return (String) getSecurityCode(4, SecurityCodeLevel.Medium, false);}public static String getSecurityCode(int length, SecurityCodeLevel level, boolean isCanRepeat) {int len = length;//除去容易混淆的0和o，1和lchar[] codes = {'1', '2', '3', '4', '5', '6', '7', '8', '9','a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i','j', 'm', 'n', 'p', 'q', 'r', 's', 't','u','v', 'w', 'x', 'y', 'z','A','B','C','D','E','F','G','H','J','K','L','M','N','P','Q','R','S','T','U','V','W','X','Y','Z'};if(level==SecurityCodeLevel.Simple){codes= Arrays.copyOfRange(codes,0,9);}else if (level==SecurityCodeLevel.Medium){codes= Arrays.copyOfRange(codes,0,33);}int n=codes.length;//抛出运行时异常if (len>n&&isCanRepeat==false){throw new RuntimeException(String.format("调用securitycode.getSecurityCode(%1$s,len,level,isCanRepeat,n)"));}char[] result=new char[len];//判断能否出现重复的字符if (isCanRepeat){for(int i=0;i<result.length;i++){//索引0 and n-1int r=(int)(Math.random()*n);//将result中的第i个元素设为codes[r]存放的数值result[i]=codes[r];}}else {for (int i=0;i<result.length;i++){int r=(int)(Math.random()*n);//将result中的第i个元素设为codes[r]存放的数值result[i]=codes[r];codes[r]=codes[n-1];n--;}}return String.valueOf(result);}
}

4.生成验证码图片（它是基于生成验证码字符串类的）CreateVerificationCodeImage.java

package bean;import java.awt.*;
import java.awt.image.BufferedImage;
import java.util.Random;/*** 可生成数字，大写，小写字母及三者混合类型的验证码，支持自定义干扰线，图文颜色*/
public class CreateVerificationCodeImage {private String securityCode;public CreateVerificationCodeImage(String securityCode){this.securityCode=securityCode;}//高度private static final int CAPTCHA_HEIGHT = 35;//宽度private static final int CAPTCHA_WIDTH  = 100;//数字的长度//private static final int NUMBER_CNT     = 6;private Random r = new Random();//  字体private String[] fontNames = { "宋体", "华文楷体", "黑体", "华文新魏", "华文隶书", "微软雅黑", "楷体_GB2312" };//private String[] fontNames = { "宋体",  "黑体", "微软雅黑"};/*** 机能概要:生成随机的颜色* @return*/private Color randomColor() {int red = r.nextInt(150);int green = r.nextInt(150);int blue = r.nextInt(150);return new Color(red, green, blue);}/*** 机能概要:生成随机的字体* @return*/private  Font randomFont() {int index = r.nextInt(fontNames.length);String fontName = fontNames[index];// 生成随机的字体名称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)int size = r.nextInt(5) + 24; // 生成随机字号, 24 ~ 28// int size = r.nextInt(5) + 15; // 生成随机字号, 20 ~ 24return new Font(fontName, style, size);}// 画干扰线private  void drawLine(BufferedImage image) {int num = 5;// 一共画5条Graphics2D g2 = (Graphics2D) image.getGraphics();for (int i = 0; i < num; i++) {// 生成两个点的坐标，即4个值int x1 = r.nextInt(CAPTCHA_WIDTH);int y1 = r.nextInt(CAPTCHA_HEIGHT);int x2 = r.nextInt(CAPTCHA_WIDTH);int y2 = r.nextInt(CAPTCHA_HEIGHT);g2.setStroke(new BasicStroke(1.5F));g2.setColor(randomColor()); // 随机生成干扰线颜色g2.drawLine(x1, y1, x2, y2);// 画线}}// 创建BufferedImage，生成图片public BufferedImage createImage() {BufferedImage image = new BufferedImage(CAPTCHA_WIDTH, CAPTCHA_HEIGHT, BufferedImage.TYPE_INT_RGB);Graphics2D g2 = (Graphics2D) image.getGraphics();// 背景色,白色g2.setColor(new Color(255, 255, 255));g2.fillRect(0, 0, CAPTCHA_WIDTH, CAPTCHA_HEIGHT);// 向图片中画4个字符  String securityCodefor (int i = 0; i < securityCode.length(); i++) {// 循环四次，每次生成一个字符String s = securityCode.charAt(i) + "";// 随机生成一个字母// float x = i * 1.0F * CAPTCHA_WIDTH / NUMBER_CNT; // 设置当前字符的x轴坐标float x = i * 1.0F * CAPTCHA_WIDTH / 4+7F; // 设置当前字符的x轴坐标g2.setFont(randomFont()); // 设置随机字体g2.setColor(randomColor()); // 设置随机颜色g2.drawString(s, x, CAPTCHA_HEIGHT-7); // 画图,依次将字符写入到图片的相应位置-------------------}drawLine(image); // 添加干扰线return image;}
}

5）调用工具类的生成验证码图片的方法，在通过response对象，将图片流返回给前端，有img标签的src属性负责解析：ImageCodeServelt.java
映射的url-patten: /imageCode

package servlet;import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;
import jakarta.servlet.http.HttpSession;import java.io.IOException;import javax.imageio.ImageIO;import bean.CreateVerificationCode;
import bean.CreateVerificationCodeImage;public class ImageCodeServelt extends HttpServlet {private static final long serialVersionUID = 1L;protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {String vericode= CreateVerificationCode.getSecurityCode();HttpSession session=request.getSession();session.setAttribute("verityCode",vericode);//设置返回的内容response.setContentType("img/jpeg");//浏览器不缓存响应内容--验证码图片，点一次就要刷新一次，所以不能有缓存出现response.setHeader("Pragma","No-cache");response.setHeader("Cache-Control","no-cache");//设置验证码失效时间response.setDateHeader("Expires",0);//以字节流发过去，交给img的src属性去解析即可ImageIO.write(new CreateVerificationCodeImage(vericode).createImage(),"JPEG",response.getOutputStream());}protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {doGet(request, response);}}