public class MyDataSource {

    private static LinkedList<Connection> pool = new LinkedList<>();

    private static final int INIT_CONNECTIONS = 10;

    private static final String DRIVER_NAME = "com.mysql.jdbc.Driver";

    private static final String URL = "";

    private static final String USER = "";

    private static final String PASSWORD = "";

    static {

        try {

            Class.forName(DRIVER_NAME);

            for (int i = 0; i < INIT_CONNECTIONS; i++) {

                Connection connection = DriverManager.getConnection(URL, USER, PASSWORD);

                pool.addLast(connection);

            }

        } catch (Exception e) {

            e.printStackTrace();

        }

    }

    public Connection getConnection() {

        synchronized (pool) {

            while (pool.size() <= 0) {

                try {

                    wait();

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

            }

            if (!pool.isEmpty()) {

                return pool.removeFirst();

            }

        }

        return null;

    }

    public void releaseConnection(Connection connection) {

        if (connection != null) {

            synchronized (pool) {

                pool.addLast(connection);

                notifyAll();

            }

        }

    }

}