The Java platform module system, known under the codename Project Jigsaw, is the main feature of Java 9. If you’re not familiar yet with this feature, I recommend you to watch one of the talks about it, or read its design overview by Mark Reinhold.
In short, Project Jigsaw is aimed at replacing the error-prone “classpath” with a reliable configuration as well as breaking the monolithic JDK into modules that could be deployed and used independently.
Though the release of Java 9 is scheduled for March, 2017, an early preview of the JDK 9 with Project Jigsaw is available. For those who’d like to play with modules and learn how to define them, there is a step-by-step tutorial.
Since the implementation of the module system is under heavy development and may change, IntelliJ IDEA doesn’t provide official support for it yet. I expect it to appear closer to June, 2016 when the feature hits Feature Complete. However if you’d like to try Jigsaw with IntelliJ IDEA already, below you’ll find instructions on that. Note that the standard JDK9 can be used with IntelliJ IDEA without any limitations — just as any other JDK.
How to configure an IntelliJ IDEA project that uses Jigsaw
2) Configure a separate IntelliJ IDEA module for each Jigsaw module:
3) Specify dependencies between IntelliJ IDEA modules according to your module-info.java files:
4) Tune the Java compiler options in Settings → Build, Execution, Deployment → Compiler → Java Compiler by adding the “modulepath” parameter pointed to the project output directory:
5) Make the project via Ctrl + F9 (Cmd + F9 for OS X)
6) The trickiest thing now is how to run the application. If you want the JRE to load the services defined in your modules, instead of the “classpath” you have to use the “modulepath” parameter. This is something IntelliJ IDEA doesn’t allow you to do in the Run configuration dialog. In overcome this limitation, run your application using the command line from the built-in Terminal:
I hope you’ll find these instructions useful.