Where to place module-info.java using Java 9?

Question

I have an OSGI application and I have around 30 bundles (jar files). Today I decided to see how it works/if it works with Java 9.

So I started my application and got

WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.apache.felix.framework.util.SecureAction (file:/home/.../jar/org.apache.felix.framework-5.4.0.jar) to method java.net.URLClassLoader.addURL(java.net.URL)
WARNING: Please consider reporting this to the maintainers of org.apache.felix.framework.util.SecureAction
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

After some reading I added command line option

--add-exports java.base/java.net=org.apache.felix.framework 

and created file module-info.java with the following content:

module org.apache.felix.framework { }

And I have two questions. Where should I place this module-info.java to make jvm read it? How should I bind this module-info with org.apache.felix.framework-5.4.0.jar file/bundle/jar?

If I do everything wrong please, show me right direction for fixing this problem.

Answer 1

Generic tips:

• You should read the State of the Module System to familiarize yourself with the JPMS. Alternatively, have a look at this module system tutorial (disclaimer: I'm the author).
• As described in the answer to your other question, there is no need to create modules if you don't want to.

To answer your specific questions:

The module declaration (module-info.java) needs to go into your source root directory (e.g. src/main/java). It then has to be among the list of files to compile, so it will get turned into a module descriptor (module-info.class). Last step is to include it in the list of class files that are packaged into a JAR. (Having a module descriptor in a JAR turns it into a modular JAR. If placed on the module path, the JPMS turns it into a module.)

If you don't want to create modules after all and prefer your code to run in the unnamed module, you can allow it to access internal APIs with the placeholder ALL-UNNAMED - in the case f your warning you need to open that package to reflection:

--add-opens java.base/java.net=ALL-UNNAMED

The better solution would be to stop using internal APIs, though.

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Answer 2

You should submit a bug to Apache Felix as it's the code in org.apache.felix.framework-5.4.0.jar that is doing the illegal access and needs to be fixed. I did a quick test with newer version 5.6.8 and with --illegal-access=debug and it appears that Felix has several issues that need attention. Yes, you can temporarily eliminate the specific warning above by opening the java.net package to "ALL-UNNAMED" but that is just one or many issues.

Answer 3

Well the Jigsaw quick start is a nice way to start off with if you're kick starting a project on Java-9.

Where should I place this module-info.java to make jvm read it?

Inferring your modeule name from the declaration module org.apache.felix.framework { }, you should place the module-info.java file in your project directory at:

src/org.apache.felix.framework/module-info.java 

How should I bind this module-info with org.apache.felix.framework-5.4.0.jar file/bundle/jar?

Further to compile modules and package them(bind the module-info.class at the top level directory of your modular jar), you can use the javac and jar commands.

Sample commands for the above would be somewhat like :

$ javac --module-path mods -d mods/org.apache.felix.framework \
    src/org.apache.felix.framework/module-info.java src/org.apache.felix.framework/com/apache/felix/framework/Application.java


$ jar --create --file=mlib/org.apache.felix.framework.jar \
    --main-class=com.apache.felix.framework.Application -C mods/com.apache.felix.framework

And further you can execute the module using:

$ java -p mlib -m com.apache.felix.framework

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Also apart from The State Module System and the Quick-Start documents, for migrating existing projects to Java-9, I would suggest you to follow the JDK9 Migration Guide which states a clear step wise transition required to adapt to Java9.