Push vs Pull Model in MVC

Question

What is the difference between the push & pull models of MVC?

Is Struts2, Spring MVC Pull based?

Answer 1

Struts2, Play! and so on are all kinds of pull model implementations of the MVC pattern.

Terms "push" and "pull" refer directly to the type of implementation of the observer pattern used between View and Model. As stated in GoF Observer pattern explaination, we have:

At one extreme, which we call the push model, the subject sends observers detailed information about the change, whether they want it or not. At the other extreme is the pull model; the subject sends nothing but the most minimal notification, and observers ask for details explicitly thereafter.

This means that the implementation of push model requires that View and Model are implemented using the same language and they are executed in the the same environment. Good examples of this kind of implementation are Javascript single page applications, in which View and Model components execute inside the browser and a framework, i.e. Backbone, provides MVC (a.k.a. Observer) mechanism. Often, Model component interacts with some kind of server API, to persist and get persisted datas.

On the other hand, pull model lets you implement MVC using different technologies for View component, and Controller / Model components. In this kind of MVC, there is not an explicit use of the Observer pattern and View interacts exclusively with Controller. View component, which usually executes into the browser, sends to Controller component request of model's updates or model's state. Usually requestes are implemented using HTTP protocol. This kind of implementation requires the use of some type of "augmented HTML scripting language", such as JSP, which allows to create automatically the link between View and Controller.