Spring Web Flow allows us to develop flow-based web applications easily. A flow in a web application encapsulates a series of steps that guides the user through the execution of a business task, such as checking in to a hotel, applying for a job, checking out a shopping cart, and so on. Usually, a flow will have clear start and end points, include multiple HTTP requests/responses, and the user must go through a set of screens in a specific order to complete the flow.

In all our previous chapters, the responsibility for defining a page flow specifically lies with controllers, and we weaved the page flows into individual Controllers and Views; for instance, we usually mapped a web request to a controller, and the controller is the one who decides which logical View to return as a response.

This is simple to understand and sufficient for straightforward page flows, but when web applications get more and more complex in terms of user interaction flows, maintaining...