Reason for refactor:
In cases where one might need to use multiple observers, say region, master and regionserver; and the fact that only one class can be extended, it gives rise to following pattern:
public class BaseMasterAndRegionObserver
extends BaseRegionObserver
implements MasterObserver
class AccessController
extends BaseMasterAndRegionObserver
implements RegionServerObserver
were BaseMasterAndRegionObserver is full copy of BaseMasterObserver.
There is an example of simple case too where the current design fails.
Say only one observer is needed by the coprocessor, but the design doesn't permit extending even that single observer (see RSGroupAdminEndpoint), that leads to copy of full Bas
e...Observer class into coprocessor class leading to 1000s of lines of code and this ugly mix of 5 main functions with 100 useless functions.
Javadocs changes:
- Adds class comments on 'default' methods and expectations.
- Adds explanaiton of Exception handling in Observers' class comment. Removes redundant @throws before each function.
- Improves javadocs for a bunch of functions
- deletes empty @params in a bunch of places
Change-Id: I265738d47e8554e7b4678e88bb916a0cc7d00ab3
f444b3b542