Java 9 Spring MVC Example

This Repository is an example of how to use Spring with Java 9 modules, leveraging maven multi-modules for per module dependency management.

Intention for Writing

Interoperability between Spring and Java 9 is still very fiddly. This repository serves as a functioning example that can be used to help diagnose some common issues.

Running this example

NOTE: At the moment, you can't just dive on in and run the application inside an IDE. The support simply isn't there yet.

From the root of the project:

mvn clean install
java -jar app/target/app-1.0-SNAPSHOT-exec.jar

This will spin up a spring boot application with a two endpoints, /users/{id} that you can fire a GET request at to get some dummy output and /admin/metrics which will give you a dummy, basic metrics endpoint.

How this works

Dependency Management

Each of the modules are themselves maven modules, which a parent pom in the root of the project. The parent pom orchestrates building each of the modules.

Working with Spring

The admin and users modules don't contain a main method in them. They act as collections of all the functionality related to admins and users.

The app module then brings these in as dependencies, which can be seen in pom.xml for the app module and in the module-info.java inside /src/main in the app module.

This is configured to automatically detect beans on the classpath and in the current package or lower, so each of the modules must be of the form java9.spring.mvc.**, otherwise Spring will not detect the beans.

The advantage of this approach is that the users and admin modules don't need to know anything about how the app is running. They simply spin up the APIs they're interested in.

Weird bits

Because they're maven multi modules, you need to define the dependencies in multiple different places. It would have been preferable to define them in one place and require them in the module-info.java. Perhaps this is possible; I'm not a maven wizard so will investigate further.