Money Transfer Application

Instructions to Build & Run:

Steps to run the application from IDE:

1. Import project into any IDE like Intellij using pom.xml
2. Run App from Intellij Configuration straight away
3. (Or) Go to MoneyTransferApplication File -> Right Click -> Run

From command line:

1. Build the project using pom.xml - > mvn clean install
2. Run the application -> java -jar target/revolut-1.0-SNAPSHOT.jar

Note: Application runs on port 4567 by default.

Tech/Tools:

1. Java 8
2. Spark Java (for REST)
3. GSON (for JSON handling)
4. Junit 5 unit tests
5. Postman Client (for API test suite)

API Endpoints:

Command	HTTP Method	Description
/accounts	POST	Creates New Account (Initial Balance should be provided as input)
/accounts/:id	GET	Fetches an account of the ID passed
/accounts	GET	Fetches all the accounts
/accounts/:id/credits	GET	Fetches all the credits of an account of the ID passed
/accounts/:id/debits	GET	Fetches all the debits of an account of the ID passed
/transactions	POST	Creates New Transaction (From Account ID, To Account ID, Transaction Amount are to be provided in the input payload)
/transactions/:id	GET	Fetches a transaction of the ID passed
/transactions	GET	Fetches all the transactions

Sample Account Creation Request:

{
	"balance":200.45
}

Sample Account Creation Response:

{
    "id": 3,
    "balance": 200.45,
    "credits": [],
    "debits": []
}

Sample Transaction Creation Request:

{
	"fromAccountId" :1,
	"toAccountId" :2,
	"amount": 124.25
}

Sample Transaction Creation Response:

{
    "id": 1,
    "amount": 124.25,
    "fromAccountId": 1,
    "toAccountId": 2,
    "timestamp": "Jan 11, 2020, 12:58:21 PM"
}

PS: API test suite is checked into this repo inside resources folder which can be imported onto POSTMAN.

Implementation Details:

1. There's one main class which initiates the REST API and its controllers.
2. Both account and transaction have seperate controller classes for handlings its corresponding routes
3. Input validations are handled in a common validation utility and applied wherever necessary in controllers.
4. Service classes each having its own for handling specific operations has the ID generated and automatically assigned. In-memory data structures are used for storage.
5. A custom exception handler is registered during API initialization and sets error code to response based on the type of exception.
6. A new custom exception called "BusinessException" is created for application errors.
7. GSON is used for request parsing and response handling
8. For concurrency, reentrant read write locks are used at the time of amount transfer.