利用JavaBean和MySQL实现留言板功能

实现留言板功能需要使用到JavaBean和MySQL数据库，以下是一个简单的示例：

1. 首先创建一个名为Message的JavaBean类，用于存储留言信息。

public class Message {
    private int id;
    private String name;
    private String email;
    private String message;

    public Message() {
    }

    public Message(String name, String email, String message) {
        this.name = name;
        this.email = email;
        this.message = message;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }
}

2. 创建一个名为MessageDao的Java类，用于实现与MySQL数据库的交互。

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class MessageDao {
    private Connection connection;

    public MessageDao() {
        connection = ConnectionFactory.getConnection();
    }

    public void addMessage(Message message) {
        String sql = "INSERT INTO messages (name, email, message) VALUES (?, ?, ?)";

        try (PreparedStatement statement = connection.prepareStatement(sql)) {
            statement.setString(1, message.getName());
            statement.setString(2, message.getEmail());
            statement.setString(3, message.getMessage());

            statement.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    public List<Message> getAllMessages() {
        String sql = "SELECT * FROM messages";
        List<Message> messages = new ArrayList<>();

        try (PreparedStatement statement = connection.prepareStatement(sql)) {
            ResultSet resultSet = statement.executeQuery();

            while (resultSet.next()) {
                int id = resultSet.getInt("id");
                String name = resultSet.getString("name");
                String email = resultSet.getString("email");
                String message = resultSet.getString("message");

                Message msg = new Message(name, email, message);
                msg.setId(id);

                messages.add(msg);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }

        return messages;
    }
}

3. 创建一个名为MessageServlet的Java类，用于处理网页请求和响应。

import java.io.IOException;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/messages")
public class MessageServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    private MessageDao messageDao;

    public MessageServlet() {
        super();

        messageDao = new MessageDao();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        List<Message> messages = messageDao.getAllMessages();

        request.setAttribute("messages", messages);
        request.getRequestDispatcher("messages.jsp").forward(request, response);
    }

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String name = request.getParameter("name");
        String email = request.getParameter("email");
        String message = request.getParameter("message");

        Message msg = new Message(name, email, message);
        messageDao.addMessage(msg);

        response.sendRedirect(request.getContextPath() + "/messages");
    }
}

4. 创建一个名为messages.jsp的JSP页面，用于显示留言板界面和留言列表。

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>留言板</title>
</head>
<body>
    <h1>留言板</h1>

    <form method="post" action="messages">
        <label for="name">姓名：</label>
        <input type="text" id="name" name="name" required><br>

        <label for="email">邮箱：</label>
        <input type="email" id="email" name="email" required><br>

        <label for="message">留言：</label>
        <textarea id="message" name="message" required></textarea><br>

        <button type="submit">提交</button>
    </form>

    <hr>

    <h2>留言列表</h2>

    <c:forEach var="msg" items="${messages}">
        <div>
            <h3>${msg.name} <span>${msg.email}</span></h3>
            <p>${msg.message}</p>
        </div>
    </c:forEach>
</body>
</html>

5. 创建一个名为ConnectionFactory的Java类，用于创建MySQL数据库连接。

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class ConnectionFactory {
    private static final String URL = "jdbc:mysql://localhost:3306/messages";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "password";

    public static Connection getConnection() {
        Connection connection = null;

        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection(URL, USERNAME, PASSWORD);
        } catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        }

        return connection;
    }
}

以上是一个简单的利用JavaBean和MySQL实现留言板功能的示例，你可以根据需要进行修改和扩展。