Revolut Account transfer Service

RESTful API for money transfers between accounts.

Dependencies

• Java 11

Alternatively project can be build and run with Docker.

Tech stack

• Liquibase
• Sparkjava
• H2
• jOOQ
• REST-assured

Maven wrapper

Service is using maven wrapper, so no need setup maven execution environment.

Important notes

• Database is running completely in memory. After the application is stopped, all the data will be lost.
• Data consistency is guaranteed by append-only approach for storing the data and usage of idempotency keys.
• Pessimistic locking used for update accounts balance.

Database

Scripts to populate database schema and at startup apply changes.

Running tests

To run unit and integration tests execute the following command:

./mvnw clean verify

Running service locally

Build an executable jar:

./mvnw clean package

Then run it:

java -jar ./target/transfer-jar-with-dependencies.jar

By default server is running on port 4000. It can be changed using server.port system property, e.g.:

java -Dserver.port=4000 -jar ./target/transfer-jar-with-dependencies.jar

Building and running inside docker

First run may take some time. Provided image is not optimized for any kind of workload and can only be used for testing.

First build an image:

docker build -t transfer:latest .

Start the container using the following command:

docker run --rm -it -p 4000:4000 transfer:latest

Endpoints

All rest apis exist in http-client

Create a new account

Request: POST /api/v1/accounts

Request body:

{"currency":"USD"}

The output of the command should be similar to the following:

HTTP/1.1 201 Created
Date: Tue, 28 Jan 2020 16:00:52 GMT
Content-Type: application/json
Transfer-Encoding: chunked
Server: Jetty(9.4.18.v20190429)

{
  "accountNumber": "d00035af-46e6-4ba4-bf90-f6718bd49ab2",
  "currency": "USD"
}

accountNumber in the response is an ID of a newly created account.

Get account information

Request: GET /api/v1/accounts/:account_number

Request body: No

The output of the command should be similar to the following:

{
  "accountStatusType": "ACTIVE",
  "accountNumber": "d00035af-46e6-4ba4-bf90-f6718bd49ab2",
  "createDatetime": [2020,1,28,19,30,52,662261000],
  "balance": 0.00,
  "currency": "USD"
}

Newly created accounts always have a 0 balance.

Top-up account balance

Request: POST /api/v1/accounts/deposit

Request body: JSON document with the following properties

• transactionId - id of the deposit transaction. It is used for idempotency. If not set in request created by server.
• accountNumber - account number for top-up
• amount - amount to credit in currency of account .

The output of the command should be similar to the following:

HTTP/1.1 201 Created
Date: Tue, 28 Jan 2020 16:24:25 GMT
Content-Type: application/json
Transfer-Encoding: chunked
Server: Jetty(9.4.18.v20190429)

{
  "transactionId": "5f273e85-74fc-4eab-b5cf-1e2991c505bc"
}

Withdraw account balance

Request: POST /api/v1/accounts/withdraw

Request body: JSON document with the following properties

• transactionId - id of the deposit transaction. It is used for idempotency. If not set in request created by server.
• accountNumber - account number for top-up
• amount - amount to credit in currency of account .

The output of the command should be similar to the following:

HTTP/1.1 201 Created
Date: Tue, 28 Jan 2020 17:12:01 GMT
Content-Type: application/json
Transfer-Encoding: chunked
Server: Jetty(9.4.18.v20190429)

{
  "transactionId": "2"
}

Transfer money between accounts

Request: POST /api/v1/transfers

Request body: JSON document with the following properties

• transactionId - id of the transfer. It is used for idempotency. It should be a new random UUID every time.
• source_account_id - id of the source account. It will be debited.
• target_account_id - id of the target account. It will be credited.
• amount - amount to transfer in cents.

The output of the command should be similar to the following:

HTTP/1.1 201 Created
Date: Tue, 28 Jan 2020 17:31:26 GMT
Content-Type: application/json
Transfer-Encoding: chunked
Server: Jetty(9.4.18.v20190429)

{
  "transactionId": "3"
}

After a successful transfer, new balances can be observed by querying the account transaction list.

Get account transactions

Request: GET /api/v1//accounts/:account_number/transaction

The output of the command should be similar to the following:

HTTP/1.1 201 Created
Date: Tue, 28 Jan 2020 17:57:47 GMT
Content-Type: application/json
Transfer-Encoding: chunked
Server: Jetty(9.4.18.v20190429)

{
  "accountTransactionDTOList": [
    {
      "createDatetime": [2020,1,28,20,50,1,365024000],
      "financialAccount": 2,
      "amount": 10.00,
      "balance": 10.00,
      "transactionType": "DEPOSIT",
      "transfer": 1,
      "transactionId": "3"
    }
  ]
}