实现步骤：
目录结构：
首页index.jsp：
<%@ page contentType="text/html;charset=UTF-8" language="java" %> <html> <head> <title>首页</title> </head> <body> <%--EL表达式，用于获取当前登录的用户--%> 欢迎您：${user.username} <a href="/login.html">登录</a> <a href="/LogoutServlet">退出登录</a> </body> </html>
登录页面login.html:
<!DOCTYPE html> <html lang="en"> <head> <meta charset="UTF-8"> <title>登录</title> </head> <body> <form action="/LoginServlet" method="post"> 用户名：<input type="text" name="username"><br> 密码：<input type="password" name="password"><br> <input type="submit" value="提交"> </form> </body> </html>
登录Servlet：
package com.servlet; import com.db.DB; import com.domain.User; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import java.io.IOException; import java.io.PrintWriter; import java.util.List; @WebServlet(name = "LoginServlet") public class LoginServlet extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String username = request.getParameter("username"); String password = request.getParameter("password"); List<User> users = DB.getUsers(); for (User user : users) { if (username.equals(user.getUsername()) && password.equals(user.getPassword())) { // 将当前用户存储在session中，可以在首页中使用EL表达式获取当前登录的用户名 request.getSession().setAttribute("user", user); response.sendRedirect("/index.jsp"); return; } } request.setCharacterEncoding("utf-8"); response.setContentType("text/html;charset=utf-8"); PrintWriter out = response.getWriter(); out.write("用户名或密码错误"); } }
退出Servlet：
package com.servlet; import javax.servlet.ServletException; import javax.servlet.annotation.WebServlet; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import javax.servlet.http.HttpSession; import java.io.IOException; @WebServlet(name = "LogoutServlet") public class LogoutServlet extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { HttpSession session = request.getSession(false); if (session != null) { session.removeAttribute("user"); } response.sendRedirect("/index.jsp"); return; } }
用户类：
package com.domain; public class User { private String username; private String password; public User(String username, String password) { this.username = username; this.password = password; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } }
模拟数据库：
package com.db; import com.domain.User; import java.util.ArrayList; import java.util.List; /** * 模拟数据库 */ public class DB { private static List<User> users = new ArrayList<>(); static { users.add(new User("aaa", "123")); users.add(new User("bbb", "123")); users.add(new User("ccc", "123")); } public static List<User> getUsers() { return users; } }
web.xml:
<?xml version="1.0" encoding="UTF-8"?> <web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd" version="4.0"> <servlet> <servlet-name>LoginServlet</servlet-name> <servlet-class>com.servlet.LoginServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>LoginServlet</servlet-name> <url-pattern>/LoginServlet</url-pattern> </servlet-mapping> <servlet> <servlet-name>LogoutServlet</servlet-name> <servlet-class>com.servlet.LogoutServlet</servlet-class> </servlet> <servlet-mapping> <servlet-name>LogoutServlet</servlet-name> <url-pattern>/LogoutServlet</url-pattern> </servlet-mapping> </web-app>
实现效果：
原文：https://www.cnblogs.com/songchj-bear/p/10841761.html