JPMS (Java Platform Module System) demo

It's an open source (Apache license) very simple JPMS demo.

Goal

It's a preparation for a more ambitious objective: add support for JPMS/JIGSAW in PF4J (Plugin Framework for Java).
My opinion is that JPMS is an excellent solution for modularization of Java Platform but it adds to small value for modularization of Java applications.
I hope that PF4J can be integrated with JPMS and it will fill the gap on the modularization of Java applications.

Note: The project uses only Java 9 as dependency. PF4J is not involved in this demo.

Structure

The demo application is the same demo as PF4J demo.

In few words, this projects contains a very simple extension point (or service), Greeting

public interface Greeting {

    String getGreeting();

}

some implementations: HelloGreeting, WelcomeGreeting and a main class, Boot, that prints all the implementations:

public class Boot {

    public static void main(String[] args) {
        ServiceLoader<Greeting> providers = ServiceLoader.load(Greeting.class);
        providers.stream().forEach(provider -> {
            Greeting greeting = provider.get();
            System.out.println(greeting.getClass().getName() + " > " + greeting.getGreeting());
        });
    }

}

The directories layout is:

• api (declares Greeting as extension-point)
• app (contains Boot class as the main class of application)
• hello (provides an implementation for Greeting, HelloGreeting)
• welcome (provides another implementation for Greeting, WelcomeGreeting)

I use java.util.ServiceLoader and providers feature from module-info.java to declare services/extensions.

The project comes with a trivial run.sh linux script that allows you to run the demo from command line.

How to build and run

Requirements:

• Git
• JDK 9 (test with java -version)
• Apache Maven 3 (test with mvn -version)

Note: On my machine (Ubuntu 16.04) I use Java 9 build 9+175 for this project.

Steps:

• create a local clone of this repository (with git clone https://github.com/decebals/jpms-demo.git)
• go to project's folder (with cd jpms-demo)
• run the demo (with run.sh)

The run.sh is very simple:

# create jar file for each module, in "mods" directory
mvn clean package

# run demo
java --module-path mods --module jpms.demo.app/ro.fortsoft.jpms.demo.Boot

The first line creates the jar files for each module and put these files in mods directory.

14:11 $ ls -l mods/
total 20
-rw-rw-r-- 1 decebal decebal 2535 iun 26 23:36 jpms-demo-api-0.0.1.jar
-rw-rw-r-- 1 decebal decebal 4237 iun 26 23:36 jpms-demo-app-0.0.1.jar
-rw-rw-r-- 1 decebal decebal 2779 iun 26 23:36 jpms-demo-hello-0.0.1.jar
-rw-rw-r-- 1 decebal decebal 2820 iun 26 23:36 jpms-demo-welcome-0.0.1.jar

Note: I specified the directory mods as jar output directory in the pom.xml file:

The second line runs the demo. It contains two segments:

• --module-path mods specifies the directory of modules (mods in our case)
• --module jpms.demo.app/ro.fortsoft.jpms.demo.Boot specifies the main module and the main class

The output console of demo application is:

Running JPMS demo:
ro.fortsoft.jpms.demo.hello.HelloGreeting > Hello
ro.fortsoft.jpms.demo.welcome.WelcomeGreeting > Welcome
ro.fortsoft.jpms.demo.WhazzupGreeting > Whazzup
ro.fortsoft.jpms.demo.HowdyGreeting > Howdy

Resources

• Project Jigsaw: Module System Quick-Start Guide
• JEP 261: Module System
• Java 9 modules - JPMS basics
• Snippet: Java 9 Modules and JPMS

License

Copyright 2017 Decebal Suiu

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this work except in compliance with the License. You may obtain a copy of the License in the LICENSE file, or at:

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.