MoneyTransferRESTApi - A dead simple Java REST API(without Spring)
to transfer money between accounts

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Requirements

Java 8+

Quick Start - Run

1.In Project Root Directory,type

 java -jar money-transfer-api-1.0.jar (App will be running on http://localhost:8080 ,if nothing is running on 8080)

or

1) ./gradlew build
2) ./gradlew startApp (App will be running on http://localhost:8080 ,if nothing is running on 8080)

Run All Tests[Make sure nothing is running on port 8080]

./gradlew test

Problem

Design and implement a RESTful API (including data model and the backing implementation)
for money transfers between accounts.
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.
Implicit requirements:
1. The code produced by you is expected to be of high quality.
2. There are no detailed requirements, use common sense.

Solution

Why do I find this interesting ? The last time I worked on a rest api in java without Spring boot was in somewhere
2015 when I had the opportunity to deploy Ghana TV License payment channel - Jersey with raw java.
It's just fun to try to build without any spring magic,And I get to go low level again,NEW LEARNINGS!! 🔥🔥🔥

Assumption 1 : Java was chosen. Kotlin would have been sweeter & swifter
but why would I be on the JVM(Jungle Of The Violent Monks) & expect an easy life? 😛

Assumption 2 : Keep it simple . What's simpler than Guice+Spark+Hibernate With Repository Pattern &
a customized MVC style design? Oh,currency and account type and other negligible details that doesn't make money get lost in banking were
taken out intentionally to keep it simple.Couldn't use one of my numerous docker templates 😥

Assumption 3: API invoked by multiple systems & services?
Well,I guess we need to keep it stateless.Is that not REST commandment number 1?
Multi-threaded environment? Build for high concurrent requests ?
Did I hear someone say Sparkjava does 200 ThreadPools by default here ?

Assumption 4: Point 5 mentioned in memory,H2 inmemory db was used for this There is a code snippet which is worth a shoutout :

  @Override
    public void updateAccountBalancesAndTransactionLog(AccountEntity updatedSenderAccountBalance,
                                                       AccountEntity updatedRecieverAccountBalance,
                                                       AccountTransactionEntity accountTransactionEntity) {

        entityManager.getTransaction().begin();

        entityManager.persist(updatedSenderAccountBalance);
        entityManager.persist(updatedRecieverAccountBalance);
        entityManager.persist(updateTransactionEntity(accountTransactionEntity,
                TransactionStatus.SUCCESS,
                ""));

        entityManager.getTransaction().commit();
    }

Above code inside AccountEntityRepository ensures that nobody's money is lost anywhere,unless it's crediting my account 🏃 🏃 💥

Still curious? Checkout a 2min audio introduction of the codebase ➡️ ➡️ RIGHT HERE...

Application usage

Accounts

Create an account

The following request creates an account and returns empty body with 201 status code

    POST localhost:8080/api/accounts
    { 
    "name":"ace", 
    "emailAddress":"ace@g.com", 
    "accountBalance":5000 
    }

Response:

    HTTP 201 Created
    <Response body is empty>

Get All Accounts

The following request gets all accounts :

    GET http://localhost:8080/accounts
    

Response:

    HTTP 200 OK
   [
     {
       "id": 1,
       "name": "ace",
       "emailAddress": "ace@g.com",
       "accountBalance": 5000
     }
   ]

Delete an account

The following request deletes an account:

    DELETE localhost:8080/api/accounts/0

Response:

    HTTP 204 No Content

Create Money Transfer Transaction

Transfer money from one account to another:

    POST http://localhost:8080/accounts/1/transactions [Account with id =1 will be debited 1 and recieving account will be credited 1 
    
    { 
    "sendingAccountId":1, 
    "receivingAccountId":2, 
    "transactionAmount":1 
    }

Response:

    HTTP 201 No Content

Retrieve all money transfer transactions on specific account id

The folowing request retrieves all money transfer transactions on specific account id

    GET http://localhost:8080/accounts/1/transactions

Response:

    HTTP 200 OK
    [
      {
        "id": 3,
        "sendingAccountId": 1,
        "receivingAccountId": 2,
        "transactionAmount": 1,
        "transactionStatus": "SUCCESS",
        "dateOfTransaction": "Aug 27, 2019",
        "reason": ""
      },
      {
        "id": 4,
        "sendingAccountId": 1,
        "receivingAccountId": 2,
        "transactionAmount": 100000,
        "transactionStatus": "FAILED",
        "dateOfTransaction": "Aug 27, 2019",
        "reason": "Not Enough Balance to initiate transaction"
      }
    ]

Retrieve one account

The following request retrieves one account in the datastore

    GET http://localhost:8080/accounts/1

Response:

    HTTP 200 OK
{
  "id": 1,
  "name": "ace",
  "emailAddress": "ace@g.com",
  "accountBalance": 4999
}

Delete

Delete Account

The following request deletes an account by its id

    DELETE http://localhost:8080/accounts/1
   

Response:

    HTTP 204 No Content
 

Like every other code ,improvements can be made,here are a list of some improvements to be made :

TO-DOs / Improvements

• Presentation (HTTP) errors (status codes) should be separated from business code.
  Ideally business domain should have own set of errors which are later mapped to presentation layer errors.