The following stacktrace, taken with JFR, is highlighting a CPU consumer which could be optimised.

Stack Trace	Sample Count	Percentage(%)
java.util.IdentityHashMap.get(Object)	66	2.224
   org.jgroups.conf.ClassConfigurator.getMagicNumber(Class)	66	2.224
      org.jgroups.Message.writeHeader(Header, DataOutput)	66	2.224

One idea could be to use an ad-hoc implementation of Map which takes advantage of the key being a Class. An interesting alternative would be to avoid the map lookup altogether, by having the Header expose a method like "writeMagicNumber(DataInput to)".