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Quirky way of communicating the data source changes

• Requires manual actions of both sending the events and handling them. I.e. if I change smth in JCR and forget to send CCE, no one will ever know.
• Apps that are not related to the changed data source still have to handle its CCE and see if they should react (hence ContentConnector#canHandleItem).

We should try to expose the data source observation utilities and subscribe to them where needed.

• e.g. we have already the JCR observation mechanism that Vaadin's DataProvider can subscribe to in this or that way and just push the change notification to the UI automatically.
• Whenever we change smth in the data source the UI is notified eventually.
• For the data sources that do not have real time observation, we could easily provide a timer-based implementation that merely refreshes the UI periodically.

Benefits

• Clear and re-usable data source observation mechanism.
• Less boilerplate for the app developers

Questions

• Need to provide un-registration strategy. For some cases a mere weak-hashmap solution might work . We though should also make sure that once the view is dead, no observation left-overs are still hanging around