Use release javac option

[fvaleri]

Type of change

• Enhancement

Description

Starting JDK 9, the javac executable can accept the --release option to specify against which Java SE release you want to build the project. Unlike the -source and -target options, the compiler will detect and generate an error when using APIs that don't exist in previous releases of Java SE. This option is available in maven-compiler-plugin since version 3.6.

Using --release N is roughly equivalent to:

• for N < 9: -source N -target N -bootclasspath <documented-APIs-from-N>
• for N >= 9: -source N -target N --system <documented-APIs-from-N>

For more details see https://openjdk.org/jeps/247.

Checklist

• Make sure all tests pass

[scholzj]

What are supposed to be the benefits of this change?

[fvaleri]

What are supposed to be the benefits of this change?

The -source and -target options are not sufficient to safely compile to an older release.

By default javac compiles against the most-recent version of the platform APIs. The compiled program can therefore accidentally use APIs only available in the current version of the platform. Instead the --release flag automatically adds bootclasspath or system option to produce class files that will link against an implementation of the given platform version.

See this for a concrete example: https://www.baeldung.com/java-compiler-release-option#1-with-existing--source-and--target-option

Another important point is that you can only use public APIs when compiling with --release, which I think it's good to have, and doesn't seem to cause any problem in this project.

[scholzj]

Doesn't the article you linked suggest that this will not work as we do not have the older JDKs installed?

[fvaleri]

Doesn't the article you linked suggest that this will not work as we do not have the older JDKs installed?

No. It suggests that JDK 9 and later releases already contain the needed information to prevent you from accidental linking to symbols that did not exist in older JDK.

[scholzj]

Ok, let's try it. But if it breaks the release process I will never forget it 😉.

[scholzj]

/azp run acceptance

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[fvaleri]

Ok, let's try it. But if it breaks the release process I will never forget it 😉.

I really hope not. I didn't know that flag but found out while working on Kafka, which also switched to using this from source and target some time ago.

[ppatierno]

LGTM. Assuming it works ;-)