Home

Keywords:

• design

  • data model
  • rest api
  • money transfers
  • accounts
  • simple
  • common sense

• implementation

  • no spring
  • in-memory datastore
  • executable (jar / war)
  • tests
  • demo
  • high quality

Own requirements:

• track time
• save notes / docs
• versioning
• double booking
• gnucash

API Data Model:

Account {
	String number
	String owner
	String currency
	BigDecimal balance
}

Transfer {
	String id
	Date createdAt (=now)
	String from
	String to
	BigDecimal amount
}

Object Store Data Model:

Account {
	UUID number
	String owner
	String currency
}

Transfer {
	UUID id
	Date createdAt
	List<Split> splits
}

Split {
	UUID account
	Money amount
}

REST API resources / URLs:

POST /accounts - create account
GET /accounts?owner=XYZ - view accounts of XYZ
GET /accounts/123 - view account basic info
GET /accounts/123?fields=balance - view info with balance
GET /accounts/123/transfers - view transfers from/to this account, 307 redirect

POST /transfers - enter a new transfer
GET /transfers - debug list of transfers
GET /transfers?account=XYZ - account transfers
GET /transfers/123 - get info about the transfer

User Stories:

1. As a user I can create new accounts under my name
2. As a user I can view my accounts with their balance
3. As a user I can view my account history (incoming and outgoing transfers)
4. As a user I can transfer money between accounts
5. As a user I can view the status of the transfer

Technologies

• Java 8 SE - base
• JAX-RS & Jersey Client & Server
• Jetty - embedded servlet container
• simple own object store
• assembly/shade plugins - executable jar
• groovy & spock - unit and acceptance tests
• maven - project tool
• github - source control

Project structure

• single project with tests

Possible improvements

• json Message with details of error (to complement http status code)
• bean validation for input objects
• hateoas (very limited as part of 201 Created and Location header)
• monitoring, tracing, etc
• registration in service registry to allow discovery
• api module for DTOs and interfaces to make it easy for consumers
• Optional<> instead of nulls
• validation of transfers against account store (see incode TODOs)

Time statistics:

What	Time
Analysis and design	2h
Prototyping	7h
Impl. & testing	14h
Self review	1h
Total	24h