Spring Boot like money-transfer application without Spring

Assignment: Create REST application for sending money between accounts without full-blown frameworks like Spring.

Note 1: If not specified module is written in Kotlin.

Note 2: JavaDoc or KotlinDoc is intentionally not present.

Module main-application

• contains main CLI class BankApplication
• generated .jar has manifest with main class specified - you can run it with java -jar bank.jar command
• default host is localhost
• default port is 8080
• default H2 DB directory is current dir .
• run it with --help parameter to see all parameters
• module also contains End-to-end integration test

Module business

• contains main business logic (usually with start of DB transaction)
• BankInitializer to initialize bank internal accounts for Top-up and Withdrawal actions
• AccountService for working with accounts itself
  • createPersonalAccount - for creating PERSONAL account with specified name and zero balance
  • createTopUpAccount - for creating bank internal TOP_UP account
  • createWithdrawalAccount - for creating bank internal WITHDRAWAL account
  • findAccount - for finding account by it's id
  • findTopUpAccount - for finding most suitable top-up account
  • findWithdrawalAccount - for finding most suitable withdrawal account
• PaymentOrderService for creating payment requests and returning data about payment orders
  • receivePaymentRequest - for creating payment requests between accounts
  • topUpRequest - for topping up accounts
  • withdrawalRequest - for withdrawal requests
  • paymentOrderState - to get state of particular payment order
  • listItemsForPersonalAccounts - to list all payment order of specified personal account
  • listItemsToProcess - to list requests that could be processed (they are in RECEIVED state)
• TransactionService for some helper methods
  • calculateBalance - to calculate balance of account from credit/debit side of amount (to check if account's balance is correct)
  • findAccountTransactions - to list all transactions of specified account
• Coordinator is used to coordinate which payment orders and when they will be processed
  • it polls database for data to process and sends them to Transactor
• Transactor is used to process payment request
  • it uses optimistic locking to fail when concurrent access to data is detected by VERSION database column
  • when concurrent processing occurs only first commit wins

Module dao

• contain DAO classes to access all three DB tables
  • account table for storing information about account and it's balance
  • payment-order for storing payment requests between accounts
  • transaction for storing actual money transactions
• JOOQ is used as SQL abstraction
  • also optimistic locking is used for keeping data consistency when money transfer occurred

Module domain

• contains domain data classes
  • Account - for storing information about account like it's type, name, dateOpened, and current balance
    • types are PERSONAL, TOP_UP for cash/card top-ups, WITHDRAWAL for eg. ATM withdrawals
  • PaymentOrder - for storing information about payment order request like fromAccount and toAccount transfer, amount of money to transfer, state of order, and dateCreated when order has been created
    • states are RECEIVED, OK, and NO_FUNDS when personal account does not have enough funds to finish transaction
  • Transaction - for actual transaction. It contains reference to paymentOrder and dateTransacted information.
    • fields fromAccount, toAccount, and amount are kind of duplicates to similar filed in PaymentOrder and are here for demo purposes

Module rest

• contains Jersey definition of REST endpoints
• also defines ApplicationServletContextListener which is used as starting point for application-context
  • inspired by Spring-web module
• RestApplication registers endpoints into Jersey context and configures Jackson JSON (de)serialization.
• every endpoint has to implement Endpoint interface with servletContext field which is used to lookup application context
• endpoints are:
  • POST /api/account - to create account
  • GET /api/account/{id} - to get info about account
  • GET /api/account/{id}/calculated-balance - to get calculated balance for account
  • GET /api/account/{id}/transactions - to find all transaction for particular account
  • POST /payment-order/transfer - to create transfer request between accounts
  • POST /payment-order/top-up - to create account top-up request
  • POST /payment-order/withdrawal - to create account withdrawal request
  • GET /payment-order/{id}/state - to find state of particular payment order

Module application-context

• inspired by Spring's IOC
• contains interface ApplicationContext with definition of all beans
• beans uses constructor injection
• beans are lazy created because of .start() and .stop() nature of context itself

Module database

• written in Java
• wraps Hikari connection pool and H2 database using Database interface
  • before use .start() method has to be called
  • to free database resources .stop() has to be called
• method .getDataSource() is used with cooperation of Transactional interface from "tx module"
• this module also contains database.sql file with DDL scripts
  • and generated JOOQ meta-model from database

Module tx

• written in Java and implementation is inspired by Spring's TransactionTemplate class
• main interface is Transactional which runs actions inside current transaction
• transaction is bound to current connection from Hikari pool and saved to ThreadLocal holder
• when we do not have current transaction/connection bound to thread new one is obtained from pool
  • and returned after end of helper callback methods

Module undertow-server

• written in Java and inspired by Spring-Boot
  • how it internally run selected embedded Servlet container
• wraps Undertow HTTP server into RestServer class with .start() and .stop() methods
• using constructor you can specify:
  • host (localhost is used as default)
  • requestedPort (when 0 random port is selected)
  • servletContextListener - usually contain application context
  • applicationClass - Jersey application class to start Rest endpoints