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My understanding of Spring MVC is that the View layer is responsible for the user interface that is populated with data, the Model represents a Map of values made available to the View Layer, and the Controller controls how and what data is passed to the Model as well as what business logic is carried out. The "business logic" can be divided into one or more other layers - generally a Service layer and/or Data Access layer. Is this correct?

I've seen other explanations for the MVC pattern where the Model is considered a layer with Entities, Data Access Objects, and Services. The View is responsible for the user interface. And the Controller is the gateway between the two. I don't think this applies to Spring MVC and other implementations of MVC for web frameworks.

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Your understanding as outlined in the first paragraph is mostly correct. Where I differ slightly is in viewing Model, View and Controller as separate layers of an application (since you have references to View layer). MVC is a pattern for implementing user interfaces, which would typically be part of a Presentation layer in an application. There are other patterns for implementing the presentation layer such as MVVM, MVP, PAC, and so on besides MVC.

Spring MVC is built on top of the Spring framework. If you are familiar with the Spring framework you would know that it is one of many available Dependency Injection frameworks for Java. Spring MVC Controllers are regular Spring managed beans that can be discovered by the Spring DI container and can have other Spring beans injected into them.

Model objects in a Spring MVC application can be instances of any Java class, whether in-built data types such as String, Long, BigInteger, etc. or user-defined classes and enumerations.

Views can again be anything meaningful for an end-user - an HTML page, an XML document, a JSON document, a PDF document, an Excel spreadsheet and so on. Spring MVC does not provide any view generating mechanism out-of-the-box. However, it makes available integration to several existing view generation technologies, such as, regular JSPs, JSTL, templating engines such as Freemarker, Java, Thymeleaf and StringTemplate, reporting frameworks such as Jasper Reports, XML binding frameworks such as JAXB and Castor, JSON binding frameworks such as Jackson and GSON, and so on. The Spring MVC API is fairly easy to integrate with view generation technologies and therefore the framework can accommodate new technologies relatively easily.

Since Spring MVC is a presentation layer framework, it does not specify, recommend or enforce how business logic should be implemented. However, it is generally a good idea to keep the business logic out of the presentation layer (see SOLID principle for details). For example, if you wish to provide certain users or business partners programmatic access to your business logic, you would be better off having the business logic in a separate layer of its own which the web presentation layer would invoke. You could then create a thin layer that also invokes the same business logic layer and allows programmatic access to external users using data interchange mechanisms such as SOAP, REST, EDI, etc.

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Great, concise answer. Makes a lot of sense the way you explain it.
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MVC is the UI layer.

A model is a map of objects, representing data for your views. These objects often are JPA entities, but don't have to be. It could be a simple class representing a username and password in a login form.

Keep some logic in model classes. For example, if you want to calculate the interest rate on a loan, you could do this in a model class. For complicated logic, especially when multiple model classes are involved, use a service.

Model classes must be completely independent of views and controllers, in that they can exist without them.

A controller responds to HTTP requests. Generally it is responsible for loading the correct models and choosing the correct view, and returning this info. Controllers should be pretty dumb.

You want "fat models and skinny controllers". Keep as much logic in the model as you can.

A view is a JSP or template (like Thymeleaf or Freemarker) which can consume models. The trick is to have as little logic in a view as possible.

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