Creating and Using Custom Controllers - Visualforce

Tutorial #4: Using Standard Controllers introduced how Visualforce supports the Model-View-Controller (MVC) style of user interface creation. Controllers typically retrieve the data to be displayed in a Visualforce page, and contain code that executes in response to page actions, such as a command button being clicked. Up until this point, you’ve been using a standard controller—a set of logic provided for you out of the box by the platform. In this tutorial you create your own controller by writing Apex code.

Custom controllers contain custom logic and data manipulation that can be used by a Visualforce page. For example, a custom controller can retrieve a list of items to be displayed, make a callout to an external web service, validate and insert data, and more—and all of these operations will be available to the Visualforce page that uses it as a controller.