Virtual Wallet - A RESTful API Backend

This project creates a RESTful API backend using Java, Spring Framework, Hibernate, Maven and H2 (In-memory store) database, which provides service for a virtual wallet to track users transaction account.

How to Run

Clone this repository via git clone https://github.com/Ziruliu/virtual-wallet-backend.git.
Run mvn clean package on the command line to download all the maven dependencies and build the executable jar file.
Run java -jar target/virtual-wallet-backend-0.0.1-SNAPSHOT.jar to start the application.
By default, application will run on localhost:8080, you can change the port number by going to /src/main/resources/application.properties, and modify the server.port property.

About the Service

Following public endpoints are provided by the Wallet Service:

Create a new wallet for a user

GET /user/wallet

{
    "response": "Wallet successfully created!"
}

Each user can only have a single wallet, calling the endpoint again will result in the following response:

{
    "status": 400,
    "message": "User already has a wallet",
    "timeStamp": "2018-10-14 19:49:47"
}

Return current account balance

The initial account balance is 0.

GET /user/balance

{
    "account balance": 0
}

If the wallet has not been created yet, it will result in the following response:

{
    "status": 400,
    "message": "Wallet Not Exist",
    "timeStamp": "2018-10-14 20:00:20"
}

And it applyes to other requests as well.

Perform a deposit transaction on the account

GET /user/deposit/100

{
    "id": 1,
    "type": "Deposit",
    "amount": 100,
    "timestamp": "2018-10-14 20:03:07"
}

Only positive amount will be accepted, a negative amount will result in the following response:

{
    "status": 400,
    "message": "Please enter a positive amount",
    "timeStamp": "2018-10-14 20:04:23"
}

A deposit transaction will add the amount to the account balance:

GET /user/balance

{
    "account balance": 100
}

Perform a withdrawal transaction on the account

GET /user/withdrawal/50

{
    "id": 2,
    "type": "Withdrawal",
    "amount": 50,
    "timestamp": "2018-10-14 20:09:13"
}

If withdrawal amount make the account balance goes beyond zero, it will result in the following response:

GET /user/withdrawal/100

{
    "status": 400,
    "message": "Withdrawal amount cannot exceed 50",
    "timeStamp": "2018-10-14 20:11:06"
}

Return last N transactions

GET /user/history/2

[
    {
        "id": 2,
        "type": "Withdrawal",
        "amount": 50,
        "timestamp": "2018-10-14 20:09:13"
    },
    {
        "id": 1,
        "type": "Deposit",
        "amount": 100,
        "timestamp": "2018-10-14 20:03:07"
    }
]

If N is large than the total transactions, all transactions will be returned:

GET /user/history/100

[
    {
        "id": 2,
        "type": "Withdrawal",
        "amount": 50,
        "timestamp": "2018-10-14 20:09:13"
    },
    {
        "id": 1,
        "type": "Deposit",
        "amount": 100,
        "timestamp": "2018-10-14 20:03:07"
    }
]

Exceptions

Following custom exceptions are implemented in this project:

HasWalletException
NegativeAccountBalanceException
NegativeAmountException
WalletNotException

Concurrency

Concurrency is enforced by adding Async annotation to the two methos: getBalance(), get_last_N_transactions(int N) at \src\main\java\com\ziruliu\backend\service\WalletService.java.

Aysnc Executor Confirguation:

@Bean(name = "asyncExecutor")
    public Executor asyncExecutor() {
        ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
        executor.setCorePoolSize(5);
        executor.setMaxPoolSize(5);
        executor.setQueueCapacity(500);
        executor.setThreadNamePrefix("WalletService-");
        executor.initialize();
        return executor;
    }

Testing

There are a total of 8 custom test cases at \src\test\java\com\ziruliu\backend\VirtualWalletBackendApplicationTests.java.

Ziruliu/virtual-wallet-backend