The Web Tier will normally consist of three kinds of objects:
Controller: Controller objects, like Spring MVC Controllers and Struts Actions, are responsible for processing user input as presented in HTTP requests, invoking the necessary business service layer functionality, and returning the required model for display.
Model: Objects containing data resulting from the execution of business logic and which must be displayed in the response.
View: Objects responsilbe for rendering the model to the response. The mechanism required will differ between different view tchnologies such as JSP, Velocity templates, or conceptually different approachees such as PDF or Excel. views are not responsible for updating data or even obtainning data; they merely serve to display Model data that has been added been provided by the relevant Controller.