Modularizing your code

As our shop application grew in size, we added code but we never went back to see how the components are interrelated. The following figure shows the classes involved in our application and the dependency links between them:

A diagram of the classes involved in the shop application and the dependency links between them. Note that the models.db.Schema component has no equivalent in the Java version.

We observe that there are many interdependencies between the parts of the application. Of course, controllers depend on services, but we also see that both services and controllers might depend on a web service client (for example, the OAuth controller and the SocialNetwork service in our case). More importantly, the same applies to the Play Application class. Both controllers and services might depend on the underlying application (the Application class has methods to get the application's configuration, plugins, or classpath).

Until now, I didn't give any particular recommendation...