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Key Takeaways • Implementing applications in a modular fashion encourages good design practices, such as separation of concerns and encapsulation. • The Java Platform Module System (JPMS) lets developers define what the application’s modules are, how they are to be used by other modules, and which other modules they depend upon. • It is possible to add JPMS module definitions to applications that were already using a different system to define the application’s modules, e.g. Maven modules or Gradle subprojects.

• The JDK comes with tools to help developers migrate existing code to JPMS. • Application code can still have dependencies upon pre-Java-9 libraries, these jar files are treated as a special 'automatic' modules.

This makes it easier to migrate gradually to Java 9. This article demonstrates a case study of the changes needed by a real application in order to make use of the new Java Platform Module System (JPMS).

Note that you do not need to do this in order to use Java 9, but an understanding of the module system (often referred to as Jigsaw) will no doubt, over time, become an important skill for Java developers. I’ll walk through the steps I took to refactor a, which was already organized in a modular fashion, to use the new Java module system. Download Java 9 Firstly download and install. This is currently an early access release (this article uses 9-ea+176). Until the impact of Java 9 on your system is understood, you probably don’t want this to be the default Java version. Instead of updating $JAVA_HOME to point to the new installation, you may wish to create a new environment variable $JAVA9_HOME instead. I’ll be using this approach throughout this article. There are plenty of other tutorials that talk about some of the steps you may need to take in order to use Java 9.

We will be confining our discussion to the modularization component, but you may want to check out Oracle’s for more information. Modularity The feature you’ll hear most about in the context of Java 9 is, the introduction of modules to Java. There are lots of tutorials and articles on exactly what this is or how it works, this article will cover how you can migrate your existing code to use the new Java Platform Module System. Download Facebook Messenger For Sony Ericsson Wt13i. Many developers are surprised to learn that they don’t have to add modularity to their own code in order to use Java 9.

The is probably one of the features that concerns developers when considering Java 9, but just because that part of Jigsaw may impact developers does not mean that developers need to fully embrace modularity in order to make use of Java 9. I'm a bit concerned with the modules names used. Requires javax.websocket.api As far as I know that should be java.websocket. Specifies that Standard modules, whose specifications are governed by the JCP, must have names starting with the string 'java.' JSON-P went with 'java.json', Bean Validation when with 'java.validation'. Both of them have been endorsed as good examples by the JPMS-lead.

Stephen Colebourne proposed a which seems to be followed by open source projects outside of the JCP like and your application modules. Requires javax.websocket.server.impl This seems really unfortunate to depend on an implementation as Jigsaw is about the encapsulation of internals. In addition this seems to be required for the classes in the 'org.eclipse.jetty.websocket' package so the module name is really confusing and does not reflect the contents well. All of this would be less of an issue if Jigsaw would allow to define dependencies on a package instead of a module, a lesson OSGi learnt the hard way years ago. I haven't had much of a chance to work with Gradle and Java 9 yet, as full support for Java 9 has only just been introduced in Gradle 4.1.

This case study actually was a multi-module Gradle project initially, but when I migrated to Java 9 modules I realised I wanted to restructure the whole project - this is not a Gradle-specific problem but an issue I made for myself due to my deployment limitations. As with all questions like this, I think the answer is 'it depends' (sorry!).

I personally would want to tackle something simple with few dependencies early on to see how difficult the process is. Of course, you have to ask yourself what the value is for each module - if nothing is dependent upon your module, is there any value in turning it into a full-blown JPMS module? So I'd start simple and also check there was value in the migration for each module. Once you've tackled a couple of modules and are comfortable with the process, my instinct would be to start with the core modules and work outwards.

Of course, this could get quite complicated as changes to the core may have an impact that ripples outwards. Personally, I'd probably wait to see how others are tackling the problem before taking the plunge with an important, complex application. Of course, someone has to be first.

I have a strange feeling that this tech will share the same fate of other designs done by the house of IBM, Oracle and the rest. First it will be forcefully used by Oracle, then after many attempts it will be recognized that it is too complicated and doesn't fit nicely with other technologies. Then there will be a huge refactoring and the version 2.0 will come out with Java 10. Just like EJB 1.x, 2.x were pretty much useless and only after huge push from the community the 3.x were somewhat usable.

The module names situation may well improve now that automatic modules can define their module names without having to go all the way to being full JPMS modules. Automatic modules are a necessary evil in order to ease some of the pain of migration, and being able to define a better (or at least more standard) name for them will further ease this pain. Depending upon the *.impl* package is, I believe, part of this migration effort. Or it may even be required in this case as I am actually using websockets at a very low level - at least Jigsaw lets me be clear about this dependency (and also highlights my use of it, which should make the developer/architect question if it is needed at all - I see this exposure of what's being used a very useful part of Jigsaw). On the other hand, some of these 'requires' might even go away by the time the 'real' Java 9 comes out. Earlier versions of my module-info files for this project were MUCH more nasty, they needed to 'require' pretty much every package that was used, whether directly or indirectly, and this seems to have got much better over the last 6 months of releases.

This may improve further before the actual release of Java 9. It's difficult to tell at this point, but it's definitely true that developers are wary of adopting something that could require big changes to their architecture, especially if there are no clear gains. When I was working on library code, I definitely saw the need to encapsulate internal APIs, which is a big part of Jigsaw of course.

But for enterprise developers, even Oracle's developers are not recommending refactoring existing code bases to use JPMS unless there's a real reason to do so. I guess we'll have to wait and see.