Subject Re: [Firebird-Java] Setting multiple TransactionParameterBuffer constants on a pooled FBSimpleDataSource
Using a data source it is not possible to define the mapping of a 
isolation-level itself through a property. This feature is currently 
only available through the DriverManager JDBC url.

...Well, that's a real problem.  The initial setup required changing to use database and dataSourceClassName for loading at Runtime.  I do realize that this is a lack of understanding on my part for how to use the HikariCP with a JDBC URL and Firebird.  I can see that the beautiful createHikariFactoryDataSource() method that you provided uses the class loader to load the DataSource Class (org.firebirdsql.ds.FBSimpleDataSource)  and then calling the constructor to get the DataSource:

DataSource dataSource = (DataSource) dataSourceClass.getConstructor().newInstance();

What are the correct classes and implementation to use when loading for jdbcUrl?  I only see a jdbcUrl property on the GDSFactory class.  Bottom line:

I'm not sure how to modify the DataSource to use the correct class loader and then connect to the database using a jdbcUrl like: