boolean-uk / java-api-mvc-in-memory

Java API Model View Controller

Learning Objectives

• Use the Model View Controller architecture to organise source code

Introduction

We didn't do much to organise our code in the previous exercise - I bet you can imagine how messy it would get building an app with hundreds of classes all in the same package!

To remedy this, we often organise our code into their own packages. This is another form of encapsulation.

One common technique is named "Model, View, Controller". This involves separating our code into "layers".

Model

This is our data layer. It describes what data looks like (e.g. Users, Cars, Products) and often contains something we call a "Repository" - a class that's responsible for creating and retrieving models.

View

This is what the client interacts with. It could be a HTML page, a terminal output or a JSON response from a RESTful API. With API's, the view (JSON) is a representation of a data model.

Controller

This layer is responsible for translating interactions from the View layer into logic in our program. If a user clicks a button on a view, the controller decides what to do with that action.

Example

Consider the scenario below:

• User clicks on a "Create Product" button in a view
• A controller class might validate that the user entered a valid product name before telling the Model layer to create the product
• A repository takes care of creating the Product model in a database and lets the controller know when it's done
• The controller notifies the view that the product was created
• The view displays a "Success!" message to the user

This approach to designing a system allows us to keep things organised and modular with each layer responsible for very specific tasks. If we wanted to change our database later, we'd only need to change the Model layer without touching the Controller or View layers.

Instructions

1. Fork this repository
2. Clone your fork to your machine
3. Open the project in IntelliJ
4. Take a look in the bagels package to see an example of how an API might be structured using the MVC approach (be aware this example isn't using Spring Boot it is just being used to demonstrate the relationships between the classes).
5. Create your own Products classes and a Main class in the com.booleanuk.api package using your previous exercise as a guide along with the Bagels example to implement this API spec following an MVC approach.

Extensions

This API spec contains some additions to the core spec, including adding error responses under certain scenarios and allowing clients to optionally filter products by category.