Create MRJAR with module-info.class

[webracer999]

PR to issue #262

This creates a "Multi-Release JAR" (MRJAR). The generated jar works with Java 1.8 and Java >= 9.

For Java >= 9 a module-info.class is provided (META-INF/versions/9/module-info.class). This allows the usage of jlink-tool to generate custom java runtime image.

[bowbahdoe]

What is this provides declaration for? At first glance it doesn't seem like that class is relevant to the service loader?

[webracer999]

Thank you @bowbahdoe for your feedback!

Sorry, I forgot to mention how I created the module-info.java.
As a workaround for my project I found out that moditect can generate and inject module-info to dependencies.

I used in my project the following configuration in my pom.xml under <project> -> <build> -> <plugins>:

<plugin>
    <groupId>org.moditect</groupId>
    <artifactId>moditect-maven-plugin</artifactId>
    <version>1.0.0.Final</version>
    <executions>
        <execution>
            <id>add-module-infos</id>
            <phase>generate-resources</phase>
            <goals>
                <goal>add-module-info</goal>
            </goals>
            <configuration>
                <overwriteExistingFiles>true</overwriteExistingFiles>
                <modules>
                    <module>
                        <artifact>
                            <groupId>org.ocpsoft.prettytime</groupId>
                            <artifactId>prettytime</artifactId>
                            <version>5.0.7.Final</version>
                        </artifact>
                        <moduleInfo>
                            <name>prettytime</name>
                        </moduleInfo>
                    </module>
                </modules>
            </configuration>
        </execution>
    </executions>
</plugin>

In the PR I used the generated module-info.java. To be honest, I was and I am not sure what the provides really does.
At least the BasicJavaApp.java from https://www.ocpsoft.org/prettytime/ would also work without provides.

Do you think it is safe to delete it?

[bowbahdoe]

Nope, I found where in the code it came from

https://github.com/ocpsoft/prettytime/blob/master/core/src/main/resources/META-INF/services/org.ocpsoft.prettytime.PrettyTime

So it does seem like that is legitimate (if a bit strange)

[lincolnthree]

Yeah, I can't remember exactly why that service file was added. It may be simply so that PrettyTime can be loaded via a ServiceLoader, but... I can't honestly recall.

[webracer999]

As long as there is a defined service I think it is correct to add it to the module-info.java.

[webracer999]

I have changed the module name to reverse DNS.
It is advised according to https://stackoverflow.com/questions/43192741/how-should-i-name-my-java-9-module -> https://mail.openjdk.org/pipermail/jpms-spec-experts/2017-May/000687.html

[bowbahdoe]

I think there is nothing stopping this from being merged