transaction-manager

Context
Objectives
Approach
Schema
API System
API Flows
TDD-Red->Green->Refactor cycle
- Test Coverages
Setup
Libraries Used
Challenges
References

Context

A Small, light-weight Rest API based Java application without any framework, which does not require any server.

Objectives

Following are the primary objectives this project is based on

The REST API should be built on an embedded server which means there should be no server or container that helps these API end points run at a particular application endpoint
TDD should be enforced at every stage of the implementation
The Application implementation should be simple and scalable as if it has real time traffic with multiple users accessing the system simultaneously
The Application is meant to be Light weight hence Heavy frameworks such as Spring could not considered while implementing
Application could only rely on in memory datastores

The Approach

Based on the aforementioned objectives the system that is being built has been built based on the following approach:

Using Jersey-Server library to create a JAX-RS reliant REST API server which can run as a self contained, embedded server that can be started and stopped from a simple Java application.
Using Mockito and PowerMocktio frameworks the entire implementation is developed following the TDD strategy where fail tests -> refactor -> pass tests cycle was strictly carried on.
JAX-RS application are simple, fast, reliable at the same time scaled based on the underlying data access implementations
SQLite datastore is used to store the data without involving any sever runtime or containers to actively engage with data connections.
Hibernate-JPA library is used to leverage the advantages javax.persistence library which helps in efficient, simple and scaled database access approaches.

Schema

API System flow

API Flows

Endpoint info

Endpoint\HTTP METHOD	POST	GET
CRUD OP	CREATE	READ
/users	Create new User	List existing users
/users/1	--	Show Existing user
/users/1/accounts	Create an account for user1	List All Accounts of user 1
/users/1/accounts/1	--	Show Existing User's Chosen Account
/users/1/accounts/1/transactions	Post a transaction to the given account - payload varies	Show Selected Account transactions
/users/1/accounts/1/transactions/1	--	Show Chosen Transaction detail

Response Status Codes

Following are the response status codes that are sent as part of the system

200 - OK
304 - Not Modified
400 - Bad Request
404 - Not Found
500 - Internal Server Error

Endpoint	Applicable status codes
/users	200, 304, 500
/users/1	200, 404
/users/1/accounts	200, 400, 500
/users/1/accounts/1	200, 400, 404
/users/1/accounts/1/transactions	200, 400, 404, 500
/users/1/accounts/1/transactions/1	200, 304, 400, 404, 500,

Endpoint details

/users

GET:

curl http://localhost:8080/users

HTTP STATUS: 200

[
    {
        "city": "Pasedena",
        "dob": "11/03/1980",
        "email": "[email protected]",
        "firstName": "Leonard",
        "gender": "male",
        "id": 1,
        "lastName": "Hofstader",
        "phoneNumber": "+811297983423"
    },
    {
        "city": "Pasedena",
        "dob": "12/12/1983",
        "email": "[email protected]",
        "firstName": "Penny",
        "gender": "female",
        "id": 2,
        "lastName": "Barrington",
        "phoneNumber": "+8242312213123"
    }
]

POST:

curl -d '{"city": "Pasedena","dob": "11/03/1980","email": "[email protected]","firstName": "Leonard","gender": "male","lastName": "Hofstader","phoneNumber": "+811297983423"}' -H "Content-Type: application/json" -X POST http://localhost:8080/users/

HTTP STATUS: 201

{
    "city": "Pasedena",
    "dob": "11/03/1980",
    "email": "[email protected]",
    "firstName": "Leonard",
    "gender": "male",
    "id": 1,
    "lastName": "Hofstader",
    "phoneNumber": "+811297983423"
}

Possible error messages:

Record Creation Failed!
Required Field(s) are Invalid! Field(s) :
Unable to Find Record with given data!
Internal Server Error! Please check Logs!

/users/{user-id}

GET:

curl http://localhost:8080/users/1

HTTP STATUS: 200

{
    "city": "Pasedena",
    "dob": "11/03/1980",
    "email": "[email protected]",
    "firstName": "Leonard",
    "gender": "male",
    "id": 1,
    "lastName": "Hofstader",
    "phoneNumber": "+811297983423"
}

/users/{user-id}/accounts

GET:

curl http://localhost:8080/users/1/accounts

HTTP STATUS: 200

[
    {
        "accountNumber": "2321342SFDS12",
        "accountType": "SAVINGS",
        "balance": 123.456,
        "currency": "USD",
        "id": 1,
        "timeCreated": 1561723026458,
        "user": {
            "city": "Pasedena",
            "dob": "12/12/2019",
            "email": "[email protected]",
            "firstName": "Leonard",
            "gender": "male",
            "id": 1,
            "lastName": "Hofstader",
            "phoneNumber": "+811297983423"
        }
    }
]

POST:

curl -d '{"accountNumber" : "2321342SFDS12","accountType" : "SAVINGS","currency" : "USD","balance" : 123.456}' -H "Content-Type: application/json" -X POST http://localhost:8080/users/1/accounts

HTTP STATUS: 201

{
    "accountNumber": "2321342SFDS12",
    "accountType": "SAVINGS",
    "balance": 123.456,
    "currency": "USD",
    "id": 1,
    "timeCreated": 1561723026458,
    "user": {
        "city": null,
        "dob": null,
        "email": null,
        "firstName": null,
        "gender": null,
        "id": 1,
        "lastName": null,
        "phoneNumber": null
    }
}

Possible error messages:

Record Creation Failed!
Required Field(s) are Invalid! Field(s) :
Unable to Find Record with given data!
Internal Server Error! Please check Logs!

/users/{user-id}/accounts/{account-id}

GET:

curl http://localhost:8080/users/1/accounts/1

HTTP STATUS: 200

{
    "accountNumber": "2321342SFDS12",
    "accountType": "SAVINGS",
    "balance": 123.456,
    "currency": "USD",
    "id": 1,
    "timeCreated": 1561723026458,
    "user": {
        "city": "Pasedena",
        "dob": "12/12/2019",
        "email": "[email protected]",
        "firstName": "Leonard",
        "gender": "male",
        "id": 1,
        "lastName": "Hofstader",
        "phoneNumber": "+811297983423"
    }
}

/users/{user-id}/accounts/{account-id}/transactions

GET:

curl http://localhost:8080/users/1/accounts

HTTP STATUS: 200

{
    "message": "Record Creation Failed!"
}

POST (DEPOSIT):

curl -d '{"transactionType" : "CHEQUE_DEPOSIT","amount" : 100.00,"currency" : "USD"}' -H "Content-Type: application/json" -X POST http://localhost:8080/users/1/accounts/1

HTTP STATUS: 304

{
    "amount": 100,
    "currency": "USD",
    "fromAccount": null,
    "id": 1,
    "timeCreated": 0,
    "toAccount": {
        "accountNumber": "2321342SFDS12",
        "accountType": "SAVINGS",
        "balance": 223.45600000000002,
        "currency": "USD",
        "id": 1,
        "timeCreated": 1561723026458,
        "user": {
            "city": "Pasedena",
            "dob": "12/12/2019",
            "email": "[email protected]",
            "firstName": "Leonard",
            "gender": "male",
            "id": 1,
            "lastName": "Hofstader",
            "phoneNumber": "+811297983423"
        }
    },
    "transactionType": "CHEQUE_DEPOSIT"
}

POST (TRANSFER):

curl -d '{"transactionType" : "TRANSFFER", "fromAccountId" : 2,"amount" : 10.00,"currency" : "USD"}' -H "Content-Type: application/json" -X POST http://localhost:8080/users/1/accounts/1

HTTP STATUS: 304

{
    "amount": 100,
    "currency": "USD",
    "fromAccount": {
        "accountNumber": "1211342SFDS12",
        "accountType": "SAVINGS",
        "balance": 23.456000000000003,
        "currency": "USD",
        "id": 2,
        "timeCreated": 1561731946466,
        "user": {
            "city": "Pasedena",
            "dob": "12/12/2019",
            "email": "[email protected]",
            "firstName": "Penny",
            "gender": "female",
            "id": 2,
            "lastName": "Hofstader",
            "phoneNumber": "+811297983423"
        }
    },
    "id": 1,
    "timeCreated": 1561732053415,
    "toAccount": {
        "accountNumber": "1211342SFDS12",
        "accountType": "SAVINGS",
        "balance": 223.45600000000002,
        "currency": "USD",
        "id": 1,
        "timeCreated": 1561731933733,
        "user": {
            "city": "Pasedena",
            "dob": "12/12/2019",
            "email": "[email protected]",
            "firstName": "Leonard",
            "gender": "male",
            "id": 1,
            "lastName": "Hofstader",
            "phoneNumber": "+811297983423"
        }
    },
    "transactionType": "TRANSFER"
}

Possible transaction types:

TRANSFER
CHEQUE_DEPOSIT
CASH_DEPOSIT

Possible error messages:

Record Creation Failed!
Unable to process transaction! Currency Conversion Not enabled
Unable to process transaction! Insufficient Balance in you Account!!
Required Field(s) are Invalid! Field(s) :
Unable to Find Record with given data!
Cannot transfer within the Same Account!
Internal Server Error! Please check Logs!

/users/{user-id}/accounts/{account-id}/transactions/{transaction-id}

GET:

curl http://localhost:8080/users/1/accounts/1/transactions/1

HTTP STATUS: 200

{
    "amount": 100,
    "currency": "USD",
    "fromAccount": null,
    "id": 1,
    "timeCreated": 0,
    "toAccount": {
        "accountNumber": "2321342SFDS12",
        "accountType": "SAVINGS",
        "balance": 223.45600000000002,
        "currency": "USD",
        "id": 1,
        "timeCreated": 1561723026458,
        "user": {
            "city": "Pasedena",
            "dob": "12/12/2019",
            "email": "[email protected]",
            "firstName": "Leonard",
            "gender": "male",
            "id": 1,
            "lastName": "Hofstader",
            "phoneNumber": "+811297983423"
        }
    },
    "transactionType": "CHEQUE_DEPOSIT"
}

Error handling

All the internal errors including runtime errors are handled at controller and sent as a valid response to user following is an example

curl -d '{"accountNumber" : "2321342SFDS12","accountType" : "SAVINGS","currency" : "USD","balance" : 123.456}' -H "Content-Type: application/json" -X POST http://localhost:8080/users/1/accounts

HTTP STATUS: 304

{
    "message": "Record Creation Failed!"
}

TDD - Red->Green->Refactor cycle

Unit test and Integration test coverage

Setup and launch

installing the packages

With Tests:

$ mvn clean install -U

running tests

Unit tests:

$ mvn  test

Integration tests:

$ mvn integration-test

running server

$ java  com.revolut.assesment.project.server.EmbeddedJettyServer

Libraries Used

Following are the Libraries that are used as part of source and test cycles

    Developed in Jetbrain's IntelliJ IDE

Challenges

Had a lot of challenges in setting up environment first with maven as there was a certificate issue that was messing with my maven commands due to network provider issues
Had difficulty in choosing the embedded server library as the prime objective was to keep the application light weight
Initially started with H2 in-memory DB and found out the hard way that it cannot be alive without a server/container or a EJB environment like JBoss.
Faced quite a lot of difficulties when trying to adapt the JAX-RS framework over the jetty-server library provided by sun.net and not the glassfish one.
Chose SQLite as it was serving the purpose and lightweight but I had to write a lot of boilerplate code initially as I was not able to find any ORM support like JPA adapting to JAX-RS and embedded server format.
But after spending a lot of time researching I have found a way to make JPA from hibernate support SQLite which let me throw away all my code involving explicit connection handling.
Had issues trying to setup integration tests, tried glassfish-jersey-client and faced a lot of dependency mismatch issues but finally found the restassured.io that helped me adapt to the sun.net jersey-client library.

References

Jersey-Server based Embedded Server supporting JAX-RS: https://dzone.com/articles/lightweight-embedded-java-rest-server-without-a-fr
Enabling CORS for the Above embedded server approach: https://crunchify.com/what-is-cross-origin-resource-sharing-cors-how-to-add-it-to-your-java-jersey-web-server/
https://dzone.com/articles/how-i-test-my-java-classes-for-thread-safety
JAXRS-H2: https://github.com/dprasanthv/JAX-RS-JPA-Hibernate-H2-In-Memory-Database
JPA-SQlite: https://github.com/juniorware/sqlite-jpa/

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