Hazelcast IMap localkeyset排序

Question

Are the localkeyset for an IMap sorted? Or, is there anyway I can proxy the backing data structure to be sorted?

I am storing temporal keys in the IMap, and from time to time looking for the oldest local key. As of now, I am doing a new TreeSet(imap.localKeyset()), however, was wondering if anyway I could make the local backing data structure sorted itself.

Thanks, Sutanu

Answer 1

No, the localKeySet is not sorted and is just a regular Set. If you want to maintain the order, I would rather prefer to use Queue instead of TreeMap(unless you want to sort it based on some other parameter instead of TimeStamp of addition) and implement a localEntryListener to control this Queue.
Another option is to use TreeSet.

public class HazelcastNode {

    private static Queue localEntryQueue = new LinkedList<>();

    public HazelcastNode(){
        HazelcastInstance hz = Hazelcast.newHazelcastInstance();

        hz.getMap("hzMap").addLocalEntryListener(new MyLocalMapListner());
    }

    public static void main(String[] args){

        HazelcastNode node = new HazelcastNode();

        //Get the Head of the queue which will be the oldest local entry
        HazelcastNode.localEntryQueue.peek();
    }

    private class MyLocalMapListner implements MapListener,EntryAddedListener,
            EntryRemovedListener,
            EntryUpdatedListener,
            EntryEvictedListener,
            EntryExpiredListener{

        @Override
        public void entryAdded(EntryEvent entryEvent) {
            HazelcastNode.localEntryQueue.add(entryEvent.getKey());
        }

        @Override
        public void entryEvicted(EntryEvent entryEvent) {
            HazelcastNode.localEntryQueue.remove(entryEvent.getKey());
        }

        @Override
        public void entryExpired(EntryEvent entryEvent) {
            HazelcastNode.localEntryQueue.remove(entryEvent.getKey());
        }

        @Override
        public void entryRemoved(EntryEvent entryEvent) {
            HazelcastNode.localEntryQueue.remove(entryEvent.getKey());
        }

        @Override
        public void entryUpdated(EntryEvent entryEvent) {
        }
    }
}