Provides support for JEP 238: Multi-Release JAR Files.
Note that this plugin is not building the jar itself, but just making sure to compile using the right JDK version files which live under src/[test|main]/[java|scala]-jdk11. The packaging into a JAR you can still use your favourite plugin of choice, such as sbt-assembly or others.
addSbtPlugin("com.lightbend.sbt" % "sbt-multi-release-jar" % "0.1.2")
This plugin allows you to keep "Java 11 only" sources in:
src/main/scala-jdk11src/main/java-jdk11src/test/scala-jdk11src/test/java-jdk11
which will only be compiled (and tests would only run) if running on JDK11.
The purpose of this plugin though is not only that, it is to be able to package
such classes into the special "multi-release jar format" defined by JEP-238 (see link above).
For example this allows you to implement a specific class once using pre-JDK11 features,
and also separately using the JDK11+ features (like varhandles or other library additions).
Assuming the such implemented class is akka.stream.impl.MagicEngine for example, you'd
implement it in src/main/scala/akka/stream/impl/MagicEngine.scala
and src/main/scala-jdk11/akka/stream/impl/MagicEngine.scala, and the resulting JAR will end up containing:
akka/stream/impl/MagicEngine.class
...
META-INF/versions/11/akka/stream/impl/MagicEngine.class
In runtime, when Java 11 is used, the META-INF/versions/11/... class is automatically loaded instead of the
"normal class". This is a feature of the Java 9 Runtime and is transparent to the application itself.
Java runtimes prior to version 9 do not know about the special meaning of these directories, and thus will
simply load the "normal class" from the root of the JAR.
This summarises the main use-case of Multi-Release JARs, however feel free to read more in the JEP 238: Multi-Release JAR Files.
sbt-multi-release-jar was originally developed by Konrad @ktoso Malawski, and currently maintained by volunteer sbt-multi-release-jar team.
Yes, pull requests and opening issues are very welcome!
Please test your changes using sbt scripted.
This plugin is released under the Apache 2.0 License