How does Spring MVC relate to Service, Controller and Data Access layers in a web application?

Model - is not a Database, is not a Repositories, is not an Entity. Model is abstraction, that contains all data, that is needed to be displayed. And every View has it's own model. You can consider Model as container for data between Controller and View.

In Spring model is ModelMap parameter of method of controller.

Controller - prepares Model, to pass it to View. If model is quite simple, Controller can do it by itself.

But most of models contains a lot of data. This can be multiple Entities from database, data from configuration etc. In this case Controller use lower level tier: Service, Repository. They all help the Сontroller to build model for View.

upd: It is a purpose of Controller to connect View and Model. Controller creates and fills the Model, then chooses View and pass this created Model to the View. That's how Model and View get connection.

In Spring controllers are Controller and RestController.

View - is final point where data from Model (passed by Controller) will be displayed to user. But another role of View is get commands from user, and pass it to Controller.

In Spring this may be view of any view-engine: JSP,Freemaker,Thymeleaf.

Note: usually, Controller does not use Repository directly. Traditionally, Controller works with Service, and Service uses Repository to get data from database. So relations are following: View<-Controller->Service->Repository

A controller accepts HTTP requests and often loads or save some data (from a service or DAO), and return an HTTP response. This response could be a redirect, or a view, or some JSON or a binary file.

A controller can use services, but should avoid having much logic of its own. It can also directly use data access objects, if there's no service logic required.

The model is whatever info a view needs to do its job. It is not necessarily related to a database. For example, you could have a model in a registration form, with email address and confirmEmailAddress fields. You don't store a confirmEmailAddress field in your db, so they there is not a 1-to-1 relationship between db tables and models. Also, your model could be data for a simple calculation that is not persisted.

So let me make sure I understand ...

The user interacts with an interface to view or submit data. The user calls on the interface to view some data. That call (an HTTP Request) goes to the Dispatcher Servlet (DS).

The DS then consults the handler mapping to help it decide which Controller to use.

Once chosen, the DS passes the request onto the Controller which calls the appropriate service methods, based on GET or POST. The Service method may need to interact with a Repository, which can interact with non-volatile storage (database, XML file, text file, etc), to construct a model based on defined business logic. Once complete, the model data is returned to the DS.

The DS then consults the View Resolver on which view should be used. The View Resolver picks a defined view for the request.

The DS then forwards the request onto the View, which is presented to the user.