Gradle & Spring Boot: choose dependency with implementation

Question

I have:

• library X with pure interfaces
• libraries X1, X2, X3, ..., XN which implement interfaces from X
• SpringBoot project Y built with Gradle 4 and using X

The implementation of X depends on the client we prepare build for.

Options I have in mind:

• Conditional Gradle build gradle build -Pclient=client1 which will include only one specific implementation
• Include all implementation as dependencies and have configuration variable which will be discovered runtime and define used implementation.

Now there is a question what are the best practices to follow?

Answer 1

Both mechanisms of handling the presented problem are more or less equivalent. I find including only single dependency (namely XN) not only easier to implement using this technology stack but also more reliable:

• reliable because there's only one particular dependency found on runtime - it's impossible that spring will mess something up with DI
• easier because if only one implementation is included there's no need for manually handling DI.
• if only single implementation will be used at runtime - what's the reason for including the else?

Two important things here:

• provide a detailed log message not only which implementation is included (during build time) but also which one is used (during runtime)
• it can be done in gradle in two different ways on war level or in dependencies block. Personally I'd go for dependencies block - it make war easier to build.