XNIO is built to JDK 6 bit it appears there is a dependency on an API call only available in JDK 7.

Rob Stryker reports on WFLY-2072 that:

failing tests that show xnio has an API requirement on java7.
java.lang.NoClassDefFoundError: java/lang/ReflectiveOperationException
at org.xnio.ssl.JsseXnioSsl.<init>(JsseXnioSsl.java:81)
at org.xnio.Xnio.getSslProvider(Xnio.java:221)
at org.jboss.remoting3.remote.RemoteConnectionProvider.connect(RemoteConnectionProvider.java:188)
at org.jboss.remoting3.EndpointImpl.doConnect(EndpointImpl.java:296)
at org.jboss.remoting3.EndpointImpl.doConnect(EndpointImpl.java:251)
at org.jboss.remoting3.EndpointImpl.connect(EndpointImpl.java:349)
at org.jboss.remoting3.EndpointImpl.connect(EndpointImpl.java:337)