The ConcurrentMap interface provides the putIfAbsent() method for adding keys which are not yet present in the map in an atomic operation. However, using this method is not always convenient because in many cases the return value is not what you want: If the value is newly added, null is returned. Typically the calling code is rather interested in the value which is now stored in the map. This is a proposal to add a new putIfAbsent() method to ConcurrentUtils which returns this value.
Also, when working with a concurrent map, a typical pattern is to check whether the map contains a key. If not, a value is created and put into the map - unless another thread was faster. An example of such a use case is a map acting as a cache. ConcurrentUtils can provide support for such use cases by combining the putIfAbsent() operation with a ConcurrentInitializer: If the key is not found in the map, the initializer is called to create the corresponding value. Finally, putIfAbsent() is called to add the value to the map.