How to create a synchronized version of Google Guava's TreeMultimap

The Guava Multimaps class contains static methods for creating and decorating Multimaps, similar to what the Collections class in java.util provides for Collections and Maps.

In your case, you should use:

Multimaps.synchronizedSortedSetMultimap(TreeMultimap.create())

Similarly, if you need to get synchronized version of ListMultiMap, you could use:

Multimaps.synchronizedListMultimap(ArrayListMultimap.create());

Google Guava Official doc