Illegal SystemId causes TransformerFactory to compute an illegal classname

There are two issues.

(1) No validation in Source::setSystemId​(String systemId)
     The correctness of a SystemId is not enforced in Source::setSystemId​(String systemId), that made it possible to pass an Illegal SystemId through a Source object to TransformerFactory.

(2) No validation when computing the classname
     The implementation of TransformerFactory does not validate the SystemId it gets from a Source. When the SystemId is incorrect, it can result in an illegal classname. This is manifested when the default Java version is upgraded higher, e.g. from Java 1.1 to Java 1.5.