Can I use module-info.java if target level is 8?

Question

I know that module-info.java is recognized by jdk9+

I wonder however whether module-info.java can still be used in combination with target level 8.

E.g. I want my library to be used in java9+ projects, which will recognize it as a module exporting specific packages, but also be used in java8 projects as a plain jar file.

Yes, you can. There are various guides on the net showing that's possible. — DodgyCodeException, Jan 09 '19 at 17:44
Such a guide, which I personally find clear, is the following: https://blog.codefx.org/tools/multi-release-jars-multiple-java-versions/ — Olivier Grégoire, Jan 09 '19 at 17:54

score 5 · Answer 1 · edited Jun 20 '20 at 09:12

The Multi-Release JAR files are meant for the exact same purpose itself.

In a JDK that does not support MRJARs, only the classes and resources in the root directory will be visible, and the two packagings will be indistinguishable.

In a JDK that does support MRJARs, the directories corresponding to any later Java platform release would be ignored; it would search for classes and resources first in the Java platform-specific directory corresponding to the currently-running major Java platform release version, then search those for lower versions, and finally the JAR root.

On a Java 9 JDK, it would be as if there were a JAR-specific class path containing first the version 9 files, and then the JAR root; on a Java 8 JDK, this class path would contain only the JAR root.

For an example of this based on Maven, take a look at this - maven-jep238.

Can I use module-info.java if target level is 8?

1 Answers1