bump to OpenJDK 21

[donsizemore]

@prpfialho correctly notes that RHEL/Rocky/CentOS 10 only offers OpenJDK 21: #11563 (comment)

I've found that EPEL 10 offers OpenJDK 24: https://distro.ibiblio.org/fedora/pub/epel/10.1/Everything/x86_64/Packages/j/

Debian and Ubuntu drop old Java releases in new distributions; Dataverse currently running on Java 17 may limit it to RHEL9 and others or below until we move to a newer Java version.

[poikilotherm]

You're not wrong.

I removed some kinks recently when folks would use Java 23.

IIRC, Payara 6 supports up to Java 21 only. Not sure if Jakarta EE 10 is/will be supported on Java 25 (LTS).

Anyone using any RHEL version can just install Temurin 17, if that helps.

From a dev standpoint I would favor waiting for final arrival of Java 24+, as some very interesting language pieces made it into that "LTS" release.

I'd also suggest using our container images, which packages all the necessary stuff for you in a neat package.

[donsizemore]

FWIW, develop (as of v6.7.1) packages cleanly on OpenJDK 21, and unit tests pass:

[dls@rdmc-dls-p340 develop]$ java -version
openjdk version "21.0.8" 2025-07-15 LTS
OpenJDK Runtime Environment (Red_Hat-21.0.8.0.9-1) (build 21.0.8+9-LTS)
OpenJDK 64-Bit Server VM (Red_Hat-21.0.8.0.9-1) (build 21.0.8+9-LTS, mixed mode, sharing)

Tests run: 1767, Failures: 0, Errors: 0, Skipped: 37

[dls@rdmc-dls-p340 develop]$ ls -al target/dataverse-6.7.1.war 
-rw-r--r--. 1 dls dls 173459657 Aug  8 14:46 target/dataverse-6.7.1.war

[pdurbin]

Yes, as of the following PR, versions newer than Java 17 were made to work but we still emphasize that Java 17 is the version we test against:

• Fix @AutoService classes not being loaded at runtime when using JDK23+ for compilation #11487

[pdurbin]

I adjusted the title of this issue to only say "bump to 21" because that's what this PR does, which closes it:

• Upgrade to Payara 7 and Java 21 #12043