Struts Tutorial

 MVC Pattern

    Pattern-It means it resolve's some problem,it follows some set of rules
The MVC (Model-View-Controller) architecture the client request is first intercepted by a servlet referred as controller servlet. this servlet handles the initial processing of the request and determines which JSP page to display next. Here the controller servlet is the single point of entry, there is a clear sepration of business logic, presentation output and request processing. MCV architecture is a way of decomposing an application into three parts:

The model maintains the state and data that the application represents.
The view allows the display of information about the model to the user.
The controller allows the user to manipulate the application.
the model, the view and the controller.

MVC was originally applied in the graphical user interaction model of input, processing and output.

In Struts, the view is handled by JSPs and presentation components, the model is represented by Java Beans and the controller uses Servlets to perform its action.

A model represents an application’s data and contains the logic for accessing and manipulating that data. Any data that is part of the persistent state of the application should reside in the model objects. The business objects update the application state. ActionForm bean represents the Model state at a session or request level, and not at a persistent level. Model services are accessed by the controller for either querying or effecting a change in the model state. The model notifies the view when a state change occurs in the model.The JSP file reads information from the ActionForm bean using JSP tags. 

The view is responsible for rendering the state of the model. The presentation semantics are encapsulated within the view, therefore model data can be adapted for several different kinds of clients.The view modifies itself when a change in the model is communicated to the view. A view forwards user input to the controller.The view is simply a JSP or HTML file. There is no flow logic, no business logic, and no model information -- just tags. Tags are one of the things that make Struts unique compared to other frameworks like Velocity.

The controller is responsible for intercepting and translating user input into actions to
be performed by the model. The controller is responsible for selecting the next view based on user input and the outcome of model operations.The Controller receives the request from the browser, and makes the decision where to send the request. With Struts, the Controller is a command design pattern implemented as a servlet. The struts-config.xml file configures the Controller.


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