So far I have not been able to find a parameter to specify a datasource.
We have been using the JasperReports library in our own custom application server for a few years now. Specifying a datasource at runtime is required for our use case and was easy to implement (because the JasperReports library supports it).
I have only briefly looked at the JasperServer source code but I would like to make some time to add such functionality if it's not in there somewhere.
Any hint from a developer would be appreciated. :)