Add overload method for JSONObject parameter
Add important comment

Some methods pass parameters to the constructor of the Work class.
It is referenced by other thread. Thus it is expected that objects
referenced by parameters are not updated.

So this patch adds a caution to method document.
Add new method to check interesting and usable for JSONObject

For new Work class, interesting and usable check for JSONObject is
isolated from original method then put it to new method.
Add new Work class

For handle JSONObject directly, new Work class "JSONEventWork" is added.
Implement addtional method for handler
Integrate post logic to one method

Handler has many similar methods. It means that many similar logics
could be put to implementation class.

This patch integrates post logic to one method to prevent logic
duplication.
Remove unnecessary import

To fix checkstyle error.