Deduplicate LocalTime

[leonardehrenfried]

This implements deduplication of instances of LocalTime.

This is okay, because it's an immutable value object where one instance truly can be replaced with an equal one.

Improvement

In my current example file this can cut down the number of instances from around 30 million to a few thousand, saving around 800MB of RAM!

cc @vpaturet

Ref: #284
Ref: noi-techpark/opendatahub-mentor-otp#273

cc @rcavaliere

[vpaturet]

Looks good.
Could you document:

• thread safety: why it works.
• memory leak: why this is a limited risk.

[leonardehrenfried]

I'm actually not sure how many threads are using the adapter concurrently. If there is a chance that it's multiple, we can synchronize the map map or use a concurrent one. Any opinions?

[vpaturet]

I'm actually not sure how many threads are using the adapter concurrently. If there is a chance that it's multiple, we can synchronize the map map or use a concurrent one. Any opinions?

The Unmarshaller is documented as not thread-safe and the reference JAXB implementation creates one instance of Adapter per Unmarshaller. But this is not mandated by the spec.
Morevoer it is possible to set programatically a shared adapter on an unmarshaller: unmarshaller.setAdapter(sharedAdapter)
Since this is a public library, we need to cover this case too.
The overhead of using a ConcurrentHashMap is negligible.