public class MsSqlDaoFactory extends AbstractDaoFactory {
    @Override
    public UsbDao getUsbDAO() {
        return new UsbDaoMsSql();
    }
    @Override
    public AbstractDeviceDao getAbstractDeviceDao(){
        return new AbstractDeviceDaoMsSql();
    }
    @Override
    public  ComputeDao getComputeDao(){
        return new ComputeDaoMsSql();
    }
    public static class PoolConnection {
        Queue<Connection> connectionFreeQueue;
        Queue<Connection> connectionBusyQueue;
        final String userName = "red";
        final String password = "123";
        String connectionUrl = "jdbc:sqlserver://localhost:1433;" + "databaseName=epam;";

        private static PoolConnection poolConnection;

        private PoolConnection() {
            connectionFreeQueue = new LinkedList<Connection>();
            connectionBusyQueue = new LinkedList<Connection>();
        }

        public static PoolConnection getInstance() {
            if (poolConnection == null)
                poolConnection = new PoolConnection();
            return poolConnection;
        }

        public void releaseConnection(Connection connection) {
            connectionFreeQueue.add(connection);
            connectionBusyQueue.remove(connection);
        }

        public Connection getConnection() throws SQLException {
            if (connectionFreeQueue.isEmpty())
                connectionFreeQueue.add(java.sql.DriverManager.getConnection(connectionUrl, userName, password));
            Connection connection = connectionFreeQueue.poll();
            connectionBusyQueue.add(connection);
            return connection;
        }

    }
}