使用jsp+javabean完成用户登陆功能

User.java

package com.po;

public class User implements java.io.Serializable {
    private String username;
    private String password;

    public User() {

    }

    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;
    }
}

UserDao.java

package com.dao;

import com.po.User;

// 用户的业务逻辑类
public class UserDao {
    public static boolean userLogin(User user) {
        if (user.getUsername().equals("admin") && user.getPassword().equals("admin")) {
            return true;
        } else {
            return false;
        }
    }
}

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_3_1.xsd"
         version="3.1">
    <welcome-file-list>
        <welcome-file>login.jsp</welcome-file>
    </welcome-file-list>
</web-app>

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
  <head>
    <title>welcome</title>
  </head>
  <body>
  <form action="checking.jsp" method="get">
    <input type="text" name="username" value="" placeholder="username">
    <input type="password" name="password" value="" placeholder="password">
    <%-- JavaBean的属性要与input标签的name保持一致，这样才能通过jsp:setProperty自动设置所创建对象的属性 --%>
    <input type="submit"/>
  </form>
  JSESSIONID=<%=request.getSession().getId()%>
  </body>
</html>

checking.jsp

<%@ page import="com.dao.UserDao" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>waiting</title>
</head>
<body>
    <jsp:useBean id="user" class="com.po.User" scope="page"/>
    <%-- 如果使用其它更大的作用域，会发现只要成功登陆一次，之后即使密码错误也能成功登陆 --%>
    <jsp:setProperty name="user" property="*"/>
    <%-- 请求重定是客户端行为，不会携带上一次请求的信息 --%>
    <%-- 请求分派是服务端行为，请求的信息会一直传递下去 --%>
    <%
        if (UserDao.userLogin(user)) {
            request.getRequestDispatcher("LoginSuccess.jsp").forward(request, response);
        } else {
            response.sendRedirect("LoginFailure.jsp");
        }
    %>
</body>
</html>

LoginFailure.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    登陆失败<br>
</body>
</html>

LoginSuccess.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    登陆成功<br>
</body>
</html>

【一些问题】

1、无法避免URL重写。。。---------> 改成 POST 即可

2、通过URL绕开登陆界面直接登陆。。。

【添加的小功能】

package com.status;

import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
import java.util.Stack;

public class Online implements HttpSessionListener{
    private static Stack<String> online = new Stack<>();

    public static Stack<String> getOnline() {
        return online;
    }

    @Override
    public void sessionCreated(HttpSessionEvent httpSessionEvent) {
        online.push(httpSessionEvent.toString());
    }

    @Override
    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        online.pop();
    }
}

<?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_3_1.xsd"
         version="3.1">
    <welcome-file-list>
        <welcome-file>login.jsp</welcome-file>
    </welcome-file-list>

    <session-config>
        <session-timeout>1</session-timeout>
    </session-config>

    <listener>
        <listener-class>
            com.status.Online
        </listener-class>
    </listener>
</web-app>

<%@ page import="com.status.Online" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
    登陆成功<br>
    <hr>
    在线用户：<br>
    <%
        int i = 0;
        for (String user: Online.getOnline()) {
            out.print(++i + "、" + user + "<br>");
        }
    %>
</body>
</html>

事实上并不需要真正登陆，只要访问服务器下面的任何页面就算“在线”了。。。（因为这些行为都会导致JVM创建session）

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原文地址：https://www.cnblogs.com/xkxf/p/7040569.html