application - Framework for performing PRocessing that is required on every incoming request, plus a place to plug in application-wide services that are offered as standard plug-ins.
Dialog - Framework for managing a series of individual interactions with the same user, necessary to complete a particular business transaction, plus a mechanism for plugging in predefined dialog services that are offered as standard plug-ins.
View - Framework for elegantly combining a view tier technology that actually composes an individual HTTP response with the corresponding business logic interactions (to retrieve or modify data in the model tier), as well as handle user interface events activated by the user.
另外，2.x将利用servlet 2.4规范中的一些新特性:
Lifecycle and event listeners for requests (as well as sessions and the entire application).
Filters can be applied across RequestDispatcher calls, not only on the original request.
Ability to specify a servlet path as a welcome file, without needing an actual artifact.
Clarifications in ordering of event handler calls ensure consistent behavior across implementations.
