java - Atomically incrementing counters stored in ConcurrentHashMap

Question

I would like to collect some metrics from various places in a web app. To keep it simple, all these will be counters and therefore the only modifier operation is to increment them by 1.

The increments will be concurrent and often. The reads (dumping the stats) is a rare operation.

I was thinking to use a ConcurrentHashMap. The issue is how to increment the counters correctly. Since the map doesn't have an "increment" operation, I need to read the current value first, increment it than put the new value in the map. Without more code, this is not an atomic operation.

Is it possible to achieve this without synchronization (which would defeat the purpose of the ConcurrentHashMap)? Do I need to look at Guava ?

Thanks for any pointers.

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P.S.
There is a related question on SO (Most efficient way to increment a Map value in Java) but focused on performance and not multi-threading

UPDATE
For those arriving here through searches on the same topic: besides the answers below, there's a useful presentation which incidentally covers the same topic. See slides 24-33.

Answer 1

In Java 8:

ConcurrentHashMap<String, LongAdder> map = new ConcurrentHashMap<>();

map.computeIfAbsent("key", k -> new LongAdder()).increment();