XMLReaderFactory uses static fields for tracking if jar files on the class path were already scanned. When some jar file provides org.xml.sax.driver, it doesn't scan jars in the future and uses class already found. However, __XMLReaderFactory switches class loader before creating XMLReader, which can result into ClassNotFoundException when class providing org.xml.sax.driver is not present in the other class loader.

Tracking fields in XMLReaderFactory should be probably reset once class loader is switched and when switched back.

I'm hitting this issue when using wildfly maven plugin together with some other plugin which contains xercex dependency, xml-maven-plugin in my case.