import org.infinispan.commons.api.functional.EntryView.*;
import org.infinispan.commons.api.functional.FunctionalMap.*;
import org.infinispan.commons.marshall.MarshallableFunctions;

ReadWriteMap<String, String> readWriteMap = ...

CompletableFuture<Boolean> future = readWriteMap.eval("key1,
   MarshallableFunctions.setValueIfAbsentReturnBoolean());
future.thenAccept(stored -> System.out.printf("Value was put? %s%n", stored));