Account Money Transfer Test

Synopsis

The account money transfer application has been built by exposing a REST api to create account, deposit money and transfer money. The API description is given in a more detail bellow. The application runs in standalone mode, hence no extra application server/container is needed in order for the application to run.

Moreover, the appropriate unit and functional tests are included.

Used Frameworks

For the implementation a series of frameworks and tools have been used. Also, the application has been developed in Java 8. The frameworks:

• Dropwizard 1.1 with embedded Jetty server
• Spock framework for functional and unit testing
• Gradle as building and dependency management tool

Implementation Overview

The purpose was the implementation of a REST standalone service for money transfer between accounts. For that reason the Service - Repository pattern has been chosen. The two main domain objects that have been considered are the "account" and "transaction".

The account represents the actual account where money are getting debited and credited.

The transaction represents the actual transaction that the user can perform. A "money-transfer" is considered a transaction. The same holds for the "money-deposit".

Aside from the above entities, the accountMovementRecord is also used as part of an account's history movements ledger. Once a transaction has been created the corresponding accountMovementRecord(s) is/are created and reference the transaction's id. The record can have one of the following types: DEPOSIT, INBOUND_TRANSFER, OUTBOUND_TRANSFER. All the amounts are recorded in positive manner.

In-memory data store

For the reasons of this test a simple in-memory store has been implemented. The store has been implemented with a very basic and abstract mechanism of ACID transactionality with READ_COMMITTED isolation level. It gives the ability to create a transaction which can either commit or rollback. However, it has to be noted that the functionality is basic and for the purposes of the test in order to be able to have and demonstrate that ACID properties have been taken into account. What could be done as a future improvement is an implementation of conditions on an update operation or a type of versioning in order to ensure that no-one else has touched a previously read record.

Currency conversion

During a money transfer from an account to another a conversion on the currency is happen to the destination account's currency. In that way somebody can transfer an amount of money from an account of a currency "A" to another account of currency "B". The corresponding conversion of the amount is happen. Class CurrencyConverter is responsible for the conversion. Currently the following currencies are supported: "EUR","USD","GBP".

API

The service's API is given bellow. Also, a Postman full collection is included under the folder /postman with all the available calls. The rest implementation is under the package java/rest.

Account Resource API

- Create a new Account

Creates a new account with zero initial balance. It returns on the header "location" the url
to retrieve the details of the newly created account

• URL

  /api/account

• Method:

  POST

• Data Params

  {
    "ownerName": "name",
    "currency": "EUR | GBP | USD"
  }
  

• Success Response:

  • Code: 202
    Header: Location /api/account/{account-id}

  • Code: 400
    When the given currency is invalid 400 is returned

- Get Account

Retrieves the details for the given account id

• URL

  /api/account/{account-id}

• Method:

  GET

• Success Response:

  • Code: 200
    Content:

    {
       "accountId": "account-uuid",
       "ownerName": "owner name",
       "balance" : "40",
       "currency": "EUR",
       "status": "OPEN",
       "created": 12442425.4214242
       "modified": 12442425.4214242
    }
    

• Error Response:

  • Code: 404
    In case where the account has not been found a 404 error is returned

  • Code: 409
    In case where the account is closed

- Get Account Movements

Retrieves all the movements (deposit, transfer) for the given account id.

• URL

  /api/account/{account-id}/movements

• Method:

  GET

• Success Response:

  • Code: 200
    Content:

    "movements":
    [{
        "id": "movement id",
        "accountId": "account uuid",
        "referenceTransactionId": "transaction id",
        "money": 
        {
            "amount": "20",
            "currency": "EUR | USD | GBP"
        }
        "accountMovementType": "DEPOSIT",
        "created": 12442425.4214242
    }]
    

• Error Response:

  • Code: 404
    In case where the account has not been found a 404 error is returned

Transaction Resource API

- Create a new deposit transaction

Creates a new deposit transaction which credits a given amount of money on the selected account. It returns
on the header "Location" the url to retrieve the newly created url. It also creates a corresponding
accountMovementRecord

• URL

  /api/transaction/deposit-money

• Method:

  POST

• Data Params

  {
      "accountId": "account uuid",
      "money": 
      {
          "amount": "20",
          "currency": "EUR | USD | GBP"
      }
  }
  

• Success Response:

  • Code: 202
    Header: Location /api/transaction/{transaction-id}

• Error Response:

  • Code: 404
    In case where the account has not been found a 404 error is returned

  • Code: 400
    In case where the given amount, currency or account id are invalid.

- Create a new transfer transaction

Creates a new transfer transaction which debits a given amount of money on one account and credits another. It returns
on the header "Location" the url to retrieve the newly created url. It also creates a corresponding
accountMovementRecord(s) for both accounts.

• URL

  /api/transaction/transfer-money

• Method:

  POST

• Data Params

  {
      "fromAccountId": "account uuid to debit the amount",
      "toAccountId": "account uuid to credit the amount",
      "money": 
      {
          "amount": "20",
          "currency": "EUR | GBP | USD"
      },
      "note": "a note for the transaction"
  }
  

• Success Response:

  • Code: 202
    Header: Location /api/transaction/{transaction-id}

• Error Response:

  • Code: 404
    In case where any of the accounts has not been found a 404 error is returned

  • Code: 400
    In case where the given amount, currency or account ids are invalid.

  • Code: 409
    if the account to debit has not the required amount of money, then this code is returned too.

- Get Transaction

Retrieves a transaction by the given transaction id

• URL

  /api/transaction/{transaction-id}

• Method:

  GET

• Success Response:

  • Code: 200
    Content:

    {
        "transactionId": "transaction id",
        "debitAccountId": "the id of the account where the amount has been debited",
        "creditAccountId": "the id of the account where the amount has been credited",
        "money": 
        {
            "amount": "20",
            "currency": "EUR | USD | GBP"
        },        
        "transactionType": "DEPOSIT | WITHDRAW | TRANSFER",
        "note": "a transfer note",
        "created": 12442425.4214242
    }
    

• Error Response:

  • Code: 404
    In case where the account has not been found a 404 error is returned

  • Code: 409
    In case where any of the accounts is closed

How to run

In order to run the application gradle is needed. To build and run the service the following command is used:

./gradlew run 

To build only the application, then the following command can be used:

./gradlew clean build

The service runs on the local port 8080. So, every rest point listens on the base url http://localhost:8080.

Unit And Functional Tests

Project contains unit and functional tests under the directory src/test/groovy. On the folder unit there are the unit tests. On the folder functional/service are the functional tests which test the service's behaviour (the service has to be up and running in order for the tests to run).