如何使用没有Spring、Hibernate的纯Java创建自己的Crud Repo

在不使用Spring、Hibernate等框架的情况下，可以使用纯Java来创建一个简单的CRUD（创建、读取、更新、删除）仓库。以下是一个基本的实现示例，包括实体类、数据访问对象（DAO）和简单的数据库连接。

1. 实体类

首先，定义一个简单的实体类，例如User。

public class User {
    private int id;
    private String name;
    private String email;

    // 构造函数、getter和setter方法
    public User(int id, String name, String email) {
        this.id = id;
        this.name = name;
        this.email = email;
    }

    // Getters and Setters
    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; }
}

2. DAO接口

定义一个DAO接口，包含基本的CRUD操作。

import java.util.List;

public interface UserDao {
    void createUser(User user);
    User getUserById(int id);
    List<User> getAllUsers();
    void updateUser(User user);
    void deleteUser(int id);
}

3. DAO实现类

实现上述接口，使用JDBC进行数据库操作。

import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class UserDaoImpl implements UserDao {
    private Connection getConnection() throws SQLException {
        // 这里应该使用连接池，为了简单起见直接使用DriverManager
        return DriverManager.getConnection("jdbc:mysql://localhost:3306/mydb", "user", "password");
    }

    @Override
    public void createUser(User user) {
        String sql = "INSERT INTO users (name, email) VALUES (?, ?)";
        try (Connection conn = getConnection(); PreparedStatement stmt = conn.prepareStatement(sql)) {
            stmt.setString(1, user.getName());
            stmt.setString(2, user.getEmail());
            stmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    @Override
    public User getUserById(int id) {
        String sql = "SELECT * FROM users WHERE id = ?";
        try (Connection conn = getConnection(); PreparedStatement stmt = conn.prepareStatement(sql)) {
            stmt.setInt(1, id);
            ResultSet rs = stmt.executeQuery();
            if (rs.next()) {
                return new User(rs.getInt("id"), rs.getString("name"), rs.getString("email"));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return null;
    }

    @Override
    public List<User> getAllUsers() {
        List<User> users = new ArrayList<>();
        String sql = "SELECT * FROM users";
        try (Connection conn = getConnection(); PreparedStatement stmt = conn.prepareStatement(sql)) {
            ResultSet rs = stmt.executeQuery();
            while (rs.next()) {
                users.add(new User(rs.getInt("id"), rs.getString("name"), rs.getString("email")));
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return users;
    }

    @Override
    public void updateUser(User user) {
        String sql = "UPDATE users SET name = ?, email = ? WHERE id = ?";
        try (Connection conn = getConnection(); PreparedStatement stmt = conn.prepareStatement(sql)) {
            stmt.setString(1, user.getName());
            stmt.setString(2, user.getEmail());
            stmt.setInt(3, user.getId());
            stmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void deleteUser(int id) {
        String sql = "DELETE FROM users WHERE id = ?";
        try (Connection conn = getConnection(); PreparedStatement stmt = conn.prepareStatement(sql)) {
            stmt.setInt(1, id);
            stmt.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}