JDBC and Persistence in Java

import java.sql.*;
import java.util.*;

public class NoteDao {
    private final javax.sql.DataSource ds;
    public NoteDao(javax.sql.DataSource ds) { this.ds = ds; }

    public long insert(long userId, String text) throws SQLException {
        String sql = "INSERT INTO notes (user_id, text) VALUES (?, ?)";
        try (Connection c = ds.getConnection();
             PreparedStatement ps = c.prepareStatement(sql, Statement.RETURN_GENERATED_KEYS)) {
            ps.setLong(1, userId);
            ps.setString(2, text);
            ps.executeUpdate();
            try (ResultSet keys = ps.getGeneratedKeys()) {
                keys.next();
                return keys.getLong(1);
            }
        }
    }

    public List<String> list(long userId) throws SQLException {
        String sql = "SELECT text FROM notes WHERE user_id = ? ORDER BY id DESC";
        List<String> out = new ArrayList<>();
        try (Connection c = ds.getConnection();
             PreparedStatement ps = c.prepareStatement(sql)) {
            ps.setLong(1, userId);
            try (ResultSet rs = ps.executeQuery()) {
                while (rs.next()) out.add(rs.getString("text"));
            }
        }
        return out;
    }
}

try (Connection c = ds.getConnection()) {
    c.setAutoCommit(false);
    try {
        debit(c, fromId, amount);
        credit(c, toId, amount);
        c.commit();
    } catch (SQLException e) {
        c.rollback();
        throw e;
    }
}

HikariConfig cfg = new HikariConfig();
cfg.setJdbcUrl(System.getenv("DATABASE_URL"));
cfg.setMaximumPoolSize(10);
DataSource ds = new HikariDataSource(cfg);

import jakarta.persistence.*;

@Entity
@Table(name = "notes")
public class Note {
    @Id @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false, length = 500)
    private String text;

    // getters and setters
}