Is OOP Compatible With an Enterprise Context?

Is OOP Compatible With an Enterprise Context?

This look at object-oriented programming considers whether it holds up in an enterprise context with a simple examine using Spring, Kotlin, and Java.

This week, during a workshop related to a Java course I give at a higher education school, I noticed the code produced by the students was mostly ok — entirely procedural. In fact, though the Java language touts itself as an Object-Oriented language, it’s not uncommon to find such code developed by professional developers in enterprises. For example, the JavaBean specification is in direct contradiction of one of OOP’s main principles, encapsulation.

Another example is the widespread controller, service, and DAO architecture found equally in Java EE and Spring applications. In that context, entities are generally anemic, while all business logic is located in the service layer. While this is not bad per se, this design separates between state and behavior and sits at the opposite end of true OOP.

Both Java EE and the Spring framework enforce this layered design. For example, in Spring, there’s one annotation for every such layer: @Controller@Service, and @Repository. In the Java EE world, only @EJB instances — the service layer — can be made transactional.

This post aims to try to reconcile both the OOP paradigm and the layered architecture. I’ll be using the Spring framework to highlight my point because I’m more familiar with it, but I believe the same approach could be used for pure Java EE apps.

A Simple Use Case

Let’s have a simple use-case: from an IBAN number, find the associated account with the relevant balance. Within a standard design, this could look like:

class ClassicAccountController(private val service: AccountService) {
    fun getAccount(@PathVariable("iban") iban: String) = service.findAccount(iban)
class AccountService(private val repository: ClassicAccountRepository) {
    fun findAccount(iban: String) = repository.findOne(iban)
interface ClassicAccountRepository : CrudRepository<ClassicAccount, String>
@Table(name = "ACCOUNT")
class ClassicAccount(@Id var iban: String = "", var balance: BigDecimal = BigDecimal.ZERO)

There are a couple of issues there:

  1. The JPA specifications mandates for a no-arg constructor. Hence, it’s possible to create ClassicalAccount instances with an empty IBAN.
  2. There’s no validation of the IBAN. A full round-trip to the database is required to check if an IBAN is valid.

Note: No, there’s no currency. It’s a simple example, remember?

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