DataHandler.getInputStream, when the dh was constructed using an Object rather than a DataSource, spawns a thread and calls the ObjectDataContentHandler.writeTo. When no specific DataContentHandler for the Object has been provided, then it throws an UnSupportedDataTypeException.

Problem is the exception has to be trapped in the thread. There, a stack trace is emitted to the console, which is kind of not very cool. The client of getInputStream just gets an empty stream, and no error indication.