First, their scope,
page: Only valid page by 'forward' the current data is transferred to other pages can be acquired using pageContext ...
request: the request server again valid range, the first time can be obtained redirection
session: once again within the valid answer, in short, in the same browser for a user sessionID are the same (in the non-privacy browser regardless of how many sub-labels open) effective,
application: all users in all browsers are valid as long as the service is not canceled tomcar this value will be obtained.
Just started primary school students welcome of all the teachings of the great God!