Money Transfer RESTful API

A Java RESTful API for money transfers between users accounts (including data model and the backing implementation)

Explicit requirements

1. You can use Java, Scala or Kotlin.
2. Keep it simple and to the point (e.g. no need to implement any authentication).
3. Assume the API is invoked by multiple systems and services on behalf of end users.
4. You can use frameworks/libraries if you like (except Spring), but don't forget about requirement #2 – keep it simple and avoid heavy frameworks.
5. The datastore should run in-memory for the sake of this test.
6. The final result should be executable as a standalone program (should not require a pre-installed container/server).
7. Demonstrate with tests that the API works as expected.

Technologies

• Java 8
• Maven
• JUnit 4
• Jetty Container
• Jersey (JAX-RS)
• Jackson (JSON)
• Apache HTTP Client (for testing)

How to run app

Using Maven

mvn exec:java

From executable jar

java -jar money-transfer-app.jar

How to run unit tests

REST controllers

mvn surefire:test -Dtest=UserControllerTest
mvn surefire:test -Dtest=AccountControllerTest
mvn surefire:test -Dtest=TransactionControllerTest

Internal services

mvn surefire:test -Dtest=UserServiceTest
mvn surefire:test -Dtest=AccountServiceTest
mvn surefire:test -Dtest=TransactionServiceTest

Available Endpoints

HTTP METHOD	PATH	USAGE
POST	/user/create	create a new user
PUT	/user/{id}	update user
DELETE	/user/{id}	delete user
GET	/user/{id}	get user by id
GET	/user/all	get all users
POST	/account/create	create a new user
DELETE	/account/{id}	delete account
GET	/account/{id}	get account by id
GET	/account/user/{id}	get accounts by user id
GET	/account/{id}/balance	get account balance by id
GET	/account/all	get all accounts
POST	/transaction	perform money transfer
DELETE	/transaction/{id}	revert money transfer
GET	/transaction/{id}	get transaction by id
GET	/transaction/account/{id}	get transactions by account id
GET	/transaction/account/{id}/outcome	get outcome transactions by account id
GET	/transaction/account/{id}/income	get income transactions by account id
GET	/transaction/user/{id}	get transactions by user id
GET	/transaction/user/{id}/outcome	get outcome transactions by user id
GET	/transaction/user/{id}/income	get income transactions by user id
GET	/transaction/all	get all transactions

Entities JSON structure

User

{
    "id": 1,
    "firstName": "Aleksei",
    "lastName": "Domozhirov",
}

Account

{
    "id": 1,
    "userId": 1,
    "currencyCode": "USD",
    "balance": 100.0
}

Transaction

{
    "id": 1,
    "sourceAccountId": 1,
    "targetAccountId": 2,
    "amount": 30.0
}

Server Errors

All handled errors returns as an Error JSON object in response. For example:

{
    "status": 400,
    "message": "Cannot find account by id=1"
}

Constraints

• User cannot be deleted if there are related accounts with this User
• Supported currency codes are: USD, EUR, PLN, RUB
• Transaction amount should be positive
• Transaction cannot be reverted if ether source or target Account have been deleted
• Money transfer is not allowed between accounts with different currency

Http Status

• 200 OK
• 400 Bad Request
• 404 Not Found
• 500 Internal Server Error