We stumbled into this exception when upgrading some rest modules using the jaxws runtime to Liferay 7.2 and Java 11.
The stacktrace shows:
Caused by: java.lang.ClassNotFoundException: com.sun.xml.internal.ws.spi.ProviderImpl cannot be found by org.apache.aries.jax.rs.whiteboard_1.0.4
The problem is quite simple: com.sun.xml.internal.ws.spi.ProviderImpl was removed in Java 9. In a normal web application, this wouldn't be a problem, since we could simply upgrade to jaxws-rt 2.3.2.
The jaxws runtime should be upgraded to 2.3+ to work correctly with Java 11.