Java: multi-threaded maps: how do the implementations compare?
Collections.synchronizedMap() simply makes all the Map methods synchronized.
ConcurrentMap is really the interface you want and there are several implementations (eg ConcurrentHashMap, ConcurrentSkipList). It has several operations that Map doesn't that are important for threadsafe operations. Plus it is more granular than a synchronized Map as an operation will only lock a slice of the backing data structure rather than the entire thing.
I have no experience of the following, but I worked with a project once who swore by Javolution for real time and memory sensitive tasks.
I notice in the API there is FastMap that claims to be thread safe. As I say, I've no idea if it's any good for you, but worth a look: