Java Demo Project

This project is intended to showcase my software engineering and development skills.

It is a demo project but incorporates key software design and clean code principles.

1. Features

This project represents a backend module of a basic Store Management System (SMS), it provides APIs to:

Create cart with/without items.
Get cart details.
Add/remove items to/from cart.
Checkout cart (inc. processing applicable discount offers).

Items examples:

Bread - 1.20€ per Packet
Milk - 0.85€ per Bottle
Tuna - 1.65€ per Tin

Offers examples:

15% discount on Bread this week
Buy 2 bottles of Milk and get 50% discount on Bread
20% direct discount on cart

2. Demonstrated Skills

2.1. Design Patterns

Applied Design Pattern	Use Case	Example
Strategy	Define condition/execution strategies for different types of offers	Discount Strategies
Builder/Director	Build cart objects	Cart Builder
Factory Method	Create repositories based on config properties	Items Repository
Singleton	Maintain unique instance of several models (using CDI `@ApplicationScoped`)	Cart/Offer Services

2.2. Dependency Injection (DI)

Code maintains dependency on abstraction rather than concrete objects (Inversion of Control).
DI framework: Jakarta Context Dependency Injection (CDI).

2.3. Clean Code Principles

KISS: code is written as SIMPLE as possible.
DRY: code relies on re-usability and abstraction to prevent duplication.
YAGNI: no unnecessary functionalities are implemented (except for some cases for the sake of this demo).
Readability: descriptive & self-explanatory classes, methods, and variable names.
Convention: code follows consistent and standard naming conventions.

2.4. Code Documentation

Code is self-explanatory.
Code is documented in javadoc format.
Clarification comments are added when necessary.
Nothing is commented out!

2.5. Automated Testing

Extensive test cases for happy path and edge cases.
Unit tests organized in AAA - Arrange, Act, Assert pattern.
Testing framework: TestNG
Mocking library: Mockito

2.6. OOP & OOD Principles

Code is fully OOP (thanks to Java!).
Abstraction: code relies on abstraction to handle complexity (DI, design patterns, ...).
Encapsulation: code implements restricted access to data members and methods (with getters/setters when required).
Inheritance: classes are structured in hierarchical manner.
Polymorphism: ex. via strategy design pattern.

2.7. Additional Features

API contracts use custom deserializers to isolate api response from internal data fields (see Contracts and Adapters).
API errors follow IETF RFC 7807 standard (see APIErrorResponseJsonAdapter.java).

2.8. System Design

Used C4 model to design the system in multiple levels of abstraction.
High level diagrams can be found here.

3. Deployment

To deploy the project on your device, clone it and run the following:

Build (Maven)

To compile java files and create executable war/jar packages:

mvn clean package

Create docker network

To create docker network (first time only):

docker network create smsjavademo_net

Run docker container

To build docker image and start container:

docker-compose up --build

4. API Reference

To run APIs, simply use attached Postman collection in /docs/postman.

Ping

  GET /sms/api/engineering/ping

Create Cart

  POST /sms/api/cart

Body - raw (json): [... "itemIdentifier" ...]

Cart Details

  GET /sms/api/cart/{cartId}

Add Item

  POST /sms/api/cart/{cartId}/items

Parameter	Type	Description
`itemIdentifier`	`String`	Required. Item to be added

Remove Item

  DELETE /sms/api/cart/{cartId}/items/{itemIdentifier}

Cart Checkout

  GET /sms/api/cart/{cartId}/checkout

sinanw/sms-java-demo