Snippet for concurrentHashMap to retrieve object or create it if absent (as atomic operation)

In Java, I want to do something like this:

   Object r = map.get(t);
   if (r == null) {
      r = create(); // creating r is an expensive operation.
      map.put(t, r);  
   }

Now that snippet of code can be executed in a multithreaded environment. map can be a ConcurrentHashMap.

But how do I make that logic atomic?

Please don't give me trivial solution like a 'synchronized' block. I 'd expect this problem can be solved neatly once and for all.

try

    value = concurentMap.get(key);
    if(value == null) {
        map.putIfAbsent(key, new Value());
        value = map.get(key);
    }
    return value;