I would like to know how you divide project modules in java for monolith with possibility of transforming modules to micro-services later?
My personal naming looks like this:
com.company.shopapp.product
...product.domain (ddd, services, repositories, entities, aggregates, command handlers - everything with package scope)
...product.api (everything with public scope)
...product.controller (CQRS endpoints for commands in web perspective - (package scope))
...product.query(CQRS - package scope)
com.company.shopapp.sales
- domain
- api
- controller
- query
What we have here is basically product management context and sales context as packages.
Modules communicate each other using public interfaces (api package) only. In my project I use "..api.ProductFacade" to centralize communication points.
When my "sales" module grow i will turn it into microservice by implementing "..api.ProductFacade" interface as a "rest" or "soap" client and on the other side I will create Endpoint/RestController based on ProductFacade interface. Package "com.company.shopapp.product.api" will be transformed into extended library and added to both projects.
Edit: I can achive this out of the box using @Feign library. https://cloud.spring.io/spring-cloud-netflix/multi/multi_spring-cloud-feign.html#spring-cloud-feign-inheritance
The whole idea feels nice, but maybe you have better way to design project and ensure that breaking it into micro-services will not break whole application.