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Java RESTful API for money transfer between user accounts

mvn exec:java

• Spark Java (Light weight microservices backend framework with embedded Jetty container)
• Junit 4 (for unit testing)
• Cucumber (for acceptance testing of features)
• Mockito (for mocking database calls and methods in unit testing)
• Dagger 2 (It is very light dependency injection framework from google like Guice)
• Lombok (for creating getter/setter using annotations)
• Rest Assured (for Integration testing)

• Double check locking singleton pattren
• Builder pattren

For thread safety, i am using java 1.8 StampedLock, in which we have optimistic read lock. Which make synchronization overhead is very low.

I have used Dagger to construct services objects and inject databse layer objects in it to demo that we can use light weight DI tools in order to avoid boiler plate code of building dependencies through code. In real systems, it comes really handy to build up dependencies. Since Dagger build up dependencies on compile time, it is fast as well on runtime to fetch those dependencies.

Application starts a jetty server on localhost port 4567.I am using port method to set port to 8080.Developer can update port according.In memory hashmap based data structure initialized with some sample user, account, and transaction data to play around with.

Few example calls are given below.

• localhost:8080/user/u1
• localhost:8080/user/u2
• localhost:8080/account/a1
• localhost:8080/account/a2

TDD and BDD practice has been followed in developing the API in following areas

• Unit Testing
• Integration Testing
• Functional Testing
• Acceptance Testing

Although, acceptance testing overlaps with the functional testing in a sense that in acceptance tests , features are tested as in functional testing but in acceptance testing, the point is to write tests in such a way which can be even read by product as they are defined in English and are converted into domain language. For example, it can be defined like following

@MoneyTransfer
	Feature: Money Transfer

	Scenario: Successful money transfer
		Given Transaction request with sender account id, reciever account and amount 
	When transfer action is called
		Then amount is deducted from sender account
		And reciever will recieve amount

For the sake of this assignment, and simpicity i am using in memory data, using concurrentHashMap.I could not use transactional features of database with rollback option but in real systems for testing, it it necessary to perform tests in transactional manner and rollback after running each transaction to persist the data or use in memory databases in development environment like H2 for fast execution of tests. To mimic the rollback operation, I have reversed every transaction in the final blocks of every test which included database calls.

Sample requesta and response objects

    {
       "user" : {
                    "id":"23211",
                    "address":"test12323",
                  "CNIC":"weqjh1k2378172",
                    "email":"[email protected]",
                    "firstName":"Ali",
                    "contactNumber":"+262711",
                    "lastName":"Javed"

                 }
    }
    {
       "user" : {
                    "id":"23222",
                    "address":"wqsgq123",
                  "CNIC":"123-7895-9996-9",
                    "email":"[email protected]",
                    "firstName":"Levo",
                    "contactNumber":"+964623",
                    "lastName":"Iop"

                 }
    }

    { 
       "account" : {
                    "id": "23122",
                    "accountTitle": "TEMP2",
                    "balance": 8310,
                    "currency": "EUR",
                    "userId": "23211"
                    }
    }

{
	"fromAccount":"23122",
	"toAccount":"23ww122",
	"amount":310
}        

Sample requests and response objects

{
		"statusType": "SUCCESS",
		"data": {
    		"id": "23211",
    		"firstName": "Ali",
    		"lastName": "Javed",
    		"email": "[email protected]",
    		"CNIC": "weqjh1k2378172",
    		"address": "test12323",
    		"contactNumber": "+262711"
			},
		"message": "User for ID [23211] created successfully"
}

{
		"statusType": "SUCCESS",
		"data": {
    		"id": "23122",
    		"accountTitle": "TEMP2",
    		"balance": 8310,
    		"currency": "EUR",
    		"userId": "23211"
			},
		"message": "Account for ID [23122] created successfully"
}

{
		"statusType": "ERROR",
		"message": "User already exists against id [23211]"
}

{
		"statusType": "SUCCESS",
		"data": {
    	"reciever": {
        		"id": "23ww122",
        		"accountTitle": "TEMP2",
        		"balance": 620,
        		"currency": "EUR",
        		"userId": "231111"
    		},
    	"sender": {
        		"id": "23122",
        		"accountTitle": "TEMP2",
        		"balance": 8000,
        		"currency": "EUR",
        		"userId": "23211"
    		}
		},
		"message": "Amount transfer successfully"
}

• 200 OK: The request has succeeded
• 400 Bad Request: The request could not be understood by the server
• 404 Not Found: The requested resource cannot be found
• 417 Bad Exception: Internal server exception
• 500 Internal Server Error: The server encountered an unexpected condition