JDBC provides a standard API for relational database access. A connection pool reuses database connections rather than creating a new connection for every request.

try (Connection connection = dataSource.getConnection();
     PreparedStatement statement =
         connection.prepareStatement(
             "select id, name from users where id = ?")) {

    statement.setString(1, userId);

    try (ResultSet rs = statement.executeQuery()) {
        if (rs.next()) {
            return rs.getString("name");
        }
    }
}

Always use parameterized queries. Pool size should account for database capacity and query latency; making it huge can overload the database.