Dependency Inversion Principle Example Application

This application provides examples of DIP and how it helps to make application design better.

Repository Structure

There are 3 branches with a bit different source code but which implements the same application.

Those branches are:

• classic-approach
• layers-separation
• dip-principle (master)

Every version has business-logic within CheckConfirmation(applicationID int) function/method. Don't focus on business-logic of this method. It's simple and made up from imagination. It should not prevent you from understanding code structure, but if you are interested, I described an idea of application in the "Business Logic" section below.

classic-approach

In "classic-approach" an application implemented as a bunch of functions which calls each other to provide needed behaviour. There is no DI and no Layer Separation. Everything implemented within one package and high-level details depends on low-level modules.

layers-separation

In "layers-separation" branch low-level modules separated from high-level modules using packages. At the same time high-level details also depends on low-level modules. There are 3 packages:

• visa - This package implements our business logic (it depends on 2 packages below).
• report - This package implements results storage.
• storage - This package implements file storage.

dip-principle (master)

In "dip-principle (master)" we have final implementation of our application, but this time we provide Dependency Injection, using Dependency Inversion Principle. So in this case high-level modules don't depend on low-level modules. This implementation also shows how we can connect our business logic with CLI and Web interface, without changing logic itself. So it this case there are 2 binaries.

Business Logic

We are tourist, who wants to get VISA to go abroad. Our application provides "Visa Application Service". Using this service we can check will be the VISA approved.

• Visa Applications stored in ./data/applications.json. It has some parameters.
• Old VISAs are stored in ./data/visas.json. We need them for service business logic.

Build

Run make lint to check if code-style locally. Run make build. It will create 2 binaries inside project directory. Run make clean to remove build artifacts.

• dip-cli - Command Line Interface Application
• dip-srv - HTTP Server Application

Test

Run make test within project directory.

Run

For CLI version:

$ ./dip-cli --id 1
$ ./dip-cli --id 0

For HTTP Server version:

$ ./dip-srv
$ curl -v -X GET "http://localhost:8080/?id=1"
$ curl -v -X GET "http://localhost:8080/?id=3"