家庭控制器.java
package com.project.controller;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import com.project.entity.User;
import com.project.model.ListUsers;
import javax.annotation.Resource;
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.sql.DataSource;
@WebServlet("/home")
public class HomeController extends HttpServlet {
private static final long serialVersionUID = 1L;
@Resource(name="jdbc/MyDB")
private DataSource dataa;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String page = request.getParameter("page");
page.toLowerCase();
switch (page) {
case "home": {
List<User> listUserss = new ArrayList<>() ;
listUserss= new ListUsers().listUsers(dataa);
request.setAttribute("listUserss", listUserss);
request.getRequestDispatcher("index.jsp").forward(request, response);
}
case "listUsers":{
request.getRequestDispatcher("listUsers.jsp").forward(request, response);
}
default:
request.getRequestDispatcher("error.jsp").forward(request, response);
}
}
}
ListUsers.java
package com.project.model;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import javax.sql.DataSource;
import com.project.entity.User;
public class ListUsers {
public List<User> listUsers(DataSource dataa){
List<User> listUsers = new ArrayList<>();
//==== build SQL database ====
ResultSet re = null;
Connection connect = null;
java.sql.Statement st= null;
try {
// =====is used to establish a connection with the database.
connect =dataa.getConnection();
// Create a SQL statement string
String query = "Select * FROM newpro.users;";
st = connect.createStatement();
// Execute SQL query
re = st.executeQuery(query);
// print the result
while(re.next()) {
listUsers.add( new User(re.getString("email"),re.getString("username"),re.getInt("users_id")));
}
} catch (SQLException e) {
e.printStackTrace();
}
return listUsers;
}
}
用戶.java
package com.project.entity;
public class User {
private String email;
private String username;
private int users_id;
public User(String email,String username,int users_id) {
this.email = email;
this.username =username;
this.users_id= users_id;
}
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public int getUsers_id() {
return users_id;
}
public void setUsers_id(int users_id) {
this.users_id = users_id;
}
}
串列用戶.jsp
<%@page import="java.util.ArrayList"%>
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ page import="java.util.List" %>
<%@ page import="com.project.entity.User" %>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>List of Users</title>
<link href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css" rel="stylesheet" >
</head>
<body>
<header class="p-3 bg-dark text-white">
<div class="container">
<div class="d-flex flex-wrap align-items-center justify-content-center justify-content-lg-start">
<a href="<%=request.getContextPath()%>/home?page=home" class="d-flex align-items-center mb-2 mb-lg-0 text-white text-decoration-none">
<svg class="bi me-2" width="40" height="32" role="img" aria-label="Bootstrap"></svg>
</a>
<ul class="nav col-12 col-lg-auto me-lg-auto mb-2 justify-content-center mb-md-0">
<li class="nav-item"><a href="<%=request.getContextPath()%>/home?page=home " class="nav-link px-2 text-muted">Home</a></li>
<li class="nav-item"><a href="<%=request.getContextPath()%>/home?page=listUsers" class="nav-link px-2 text-muted">About</a></li>
</ul>
<form class="col-12 col-lg-auto mb-3 mb-lg-0 me-lg-3">
<input type="search" class="form-control form-control-dark" placeholder="Search..." aria-label="Search">
</form>
<div class="text-end">
<button type="button" class="btn btn-outline-light me-2">Login</button>
<button type="button" class="btn btn-warning">Sign-up</button>
</div>
</div>
</div>
</header>
<h1>List of Users</h1>
<hr/>
<table border="1">
<thead>
<th>username</th>
<th>email</th>
<th>user_id</th>
</thead>
<%
/*################################## This is the Error >>>>>>>>> ###################*/
List<User> listu = request.getAttribute("listUserss");
%>
</table>
<footer class="d-flex flex-wrap justify-content-between align-items-center py-3 my-4 border-top">
<p class="col-md-4 mb-0 text-muted">? 2022 Company, Inc</p>
<a href="/" class="col-md-4 d-flex align-items-center justify-content-center mb-3 mb-md-0 me-md-auto link-dark text-decoration-none">
<svg class="bi me-2" width="40" height="32"><use xlink:href="#bootstrap"></use></svg>
</a>
<ul class="nav col-md-4 justify-content-end">
<li class="nav-item"><a href="<%=request.getContextPath()%>/home?page=home " class="nav-link px-2 text-muted">Home</a></li>
<li class="nav-item"><a href="<%=request.getContextPath()%>/home?page=listUsers" class="nav-link px-2 text-muted">About</a></li>
</ul>
</footer>
<script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/js/bootstrap.bundle.min.js" integrity="sha384-u1OknCvxWvY5kfmNBILK2hRnQC3Pr17a RTT6rIHI7NnikvbZlHgTPOOmMi466C8" crossorigin="anonymous"></script>
</body>
</html>
listUsers.jsp 中的錯誤說：Type mismatch: cannot convert from Object to List<User>
uj5u.com熱心網友回復：
請投到Object. List<User>Request 的 getAttribute 方法回傳物件，它不知道在哪個類中轉換。所以你必須明確地轉換物件。確保 request.getAttribute("listUserss") 不為空，否則將拋出 NullPointerException。
<%
List<User> listu = (List<User>) request.getAttribute("listUserss");
%>
轉載請註明出處，本文鏈接：https://www.uj5u.com/caozuo/516555.html