Question

I’ve been using MVC for a long time and heard about the “Service” layer (for example in Java web project) and I’ve been wondering if that is a real architectural pattern given I can’t find a lot of information about it.

The idea of MVCS is to have a Service layer between the controller and the model, to encapsulate all the business logic that could be in the controller. That way, the controllers are just there to forward and control the execution. And you can call a Service in many controllers (for example, a website and a webservice), without duplicating code.

Answer 1

The service layer can be interpreted a lot of ways, but it’s usually where you have your core business processing logic, and sits below your MVC architecture, but above your data access architecture.

For example, you layer of a complete system may look like this:

1. View Layer: Your MVC framework & code of choice
2. Service Layer: Your Controller will call this layer’s objects to get or update Models, or other requests.
3. Data Access Objects: These are abstractions that your service layer will call to get/update the data it needs. This layer will generally either call a Database or some other system (eg: LDAP server, web service, or NoSql-type DB)

The service layer would then be responsible for:

• Retrieving and creating your ‘Model’ from various data sources (or data access objects).
• Updating values across various repositories/resources.
• Performing application-specific logic and manipulations, etc.

The Model you use in your MVC may or may not come from your services. You may want to take the results your service gives you and manipulate them into a model that’s more specific to your medium (eg: a web page).