According to Russell Ackoff “A system is not the sum of the behaviors of its parts, but the product of their interactions”. That’s why the design of those interactions is of the uttermost importance. In a Spring application, the primary means to establish relationships between application components is dependency injection (DI). With higher-level structuring approaches like Spring Modulith’s application modules in place, should the interaction of those be implemented by DI as well?

The talk presents different approaches to designing application module interactions and compares them regarding their applicability, effect on testability, consistency, error scenarios and how they affect the modularity of the system overall.