Wiki ->https://fedoraproject.org/wiki/Changes/Java21

**This is a *proposed* Change for Fedora Linux.**
This document represents a *proposed* Change. As part of the [Changes
process](https://docs.fedoraproject.org/en-US/program_management/changes_policy/),
proposals are publicly announced in order to receive community
feedback. This proposal will only be implemented if approved by the
Fedora Engineering Steering Committee.


== Summary ==
Update the system JDK in Fedora from java-17-openjdk to java-21-openjdk.

== Owner ==
* Name: [[User:pmikova| Petra Alice Mikova]]
* Email: <pmik...@redhat.com>
* Product: java and java stack
* Responsible WG: java-sig (java and java-maint)(which no longer exists)
* rcm ticket: https://pagure.io/releng/issue/11859
* named side tag ticket: TBD



=== Expected schedule ===
* During January 2024, we will create a new package, java-21-openjdk,
which will be a clone of java-latest-openjdk, which contains STS
versions of OpenJDK (currently 21) and will move to JDK 22 in
February/March.
* December 2023 I will do mass rebuild in copr
** all maintainers will be informed about the results
* January 2023 I will do second mass rebuild in copr
** all maintainers will be informed about the results
*  February 2023 mass rebuild in rawhide - side tag
** FTBFS bugs will be filed
*  February 2023 the sidetag will be merged
* Change Checkpoint: 100% Code Complete Deadline TBD
** hard deadline for feature completed

== Detailed Description ==
Fedora currently ships:
* java-1.8.0-openjdk (LTS)
* java-11-openjdk (LTS)
* java-17-openjdk (LTS), system JDK
* java-latest-openjdk (currently JDK21)
* java-21-openjdk will be cloned from java-latest-openjdk

Therefore, every package honoring the packaging rules and requiring
java via java-headless or java-devel is built in koji using
java-17-openjdk-devel and pulling java-17-openjdk during runtime (see
[https://fedoraproject.org/wiki/Java java] ). Also,
javapackaging-tools are using java-11-openjdk as hardcoded runtime
(see 
[https://fedoraproject.org/wiki/Changes/Decouple_system_java_setting_from_java_command_setting
changes]).

We were intentionally delaying jdk11 on-boarding for stability
reasons. But there is reason for this approach with 21 (for recall,
see https://fedoraproject.org/wiki/Changes/Java11)

Major incompatibility is again (as we were bumping 8->11)
encapsulation. What was hidden is now even more hidden and few more
parts were hidden. Luckily, most of the projects, when shifted to 11,
did it properly. Still few projects may hit usage of some  newly
restricted APIs.

== Feedback ==


== Benefit to Fedora ==

JDK21 was released a while ago, but compatibility with JDK 17 is good
enough and it is a stable release. Although we can expect some group
of packages to use jdk8 forever, and some other (much smaller) group
of packages stay on jdk11 for a while, the java stack should be able
to use the JDK 21. Both JDK 8 and JDK 11 will remain part of Fedora as
long as they are supported upstream, and there is a target audience in
our OS.


== Scope ==
=== To keep the java-17-openjdk (and lower versions of JDK), but to
remove its java/javac versionless provides, make java-21-openjdk the
provider of java, javac and other versionless provides, and keep
java-latest-openjdk as rolling package for STS JDKs) ===
* will guarantee fedora to be pure JDK21 distro.
* will allow maintainers of JDK21 (or higher) incompatible packages to
keep using JDK 17, JDK 11 and JDK 8
** if any package depends on a package built by JDK 21, JDK 17, JDK 11
and JDK 8 may not be able to pick up that dependency.
** this may lead to quite a lot of bundling or compat packages, but
that may be acceptable
** people developing JDK8 and JDK11 applications will very likely stay
with fedora
** we are bumping the system JDK every time a new JDK LTS comes up and
it proved itself as a good practice

While quite a lot of users will rejoice, there may be cases where
application is very hard to migrate to JDK11, so the contingency plan
should be taken very serious.
==== Bytecode version ====
* It appeared, that several applications have to be built by jdk8,
while they work fine with jdk11
* It lead to manual work on aligned libraries on 1.8 byte code
version.  see https://pagure.io/java-maint-sig/issue/7
* Other approaches how to avoid this in next update (jdk17, aprox f36,
minimal bytecode 7) were mentioned here:
https://src.fedoraproject.org/rpms/javapackages-tools/pull-request/3#comment-50266
==== Workflow ====
* announce as by
https://docs.fedoraproject.org/en-US/program_management/changes_policy/#_essential_communication
* tune java-latest-openjdk package (for all live Fedoras)
* clone java-21-openjdk package (for all live Fedoras)
* several rounds of mass rebuilds ( see
https://fedoraproject.org/w/index.php?title=Changes/Java21#Expected_schedule)
** from copr
** over side tag
** to koji
==== Change owners ====
* Feature will be implemented in
[https://fedoraproject.org/wiki/Changes/Java21#side_tag side tag]
** --target '''f40-java21'''  is tag of choice
** In its mass rebuild, approximately XYZ packages were built, and ABC
failed. FTBFS bugs filled, most of them needs manual fix later
* the JDK 17 and JDK 21 packages will be changed for this side tag
* the mass rebuild of java stack will start
** if necessary, several rounds of them
* Failures will be gathered by me and few other volunteers
** Most common issues and theirs fixes will be published
** Package maintainers will be notified in case of failure via
[https://bugzilla.redhat.com/ bugzilla]
* Depending on the fail rate, importance of failed packages and effort
to fix them
** the side tag will be merged to Fedora
** or the [https://fedoraproject.org/wiki/Changes/Java21#Contingency_Plan
contingency] plan will be activated

==== Other developers ====
* should fix their packages
** this usually means to update to newer version, which supports jdk21
* or to retire them if they appear non-fixable
* or to base them on JDK11 without much warranty (as they will need to
compat most of dependency chain)


==== Other ====
* Proposal owners:
** based on above, adapt jdk11 and jdk17 package provides
** If necessary tune the build environment

* Other developers:
** based on selected approach to tune the main build tools
*** jpackage-tools and maven will affected
** based on selected approach to tune the rpmbuild/macros
** many java package maintainers will maybe need to adapt theirs packages
*** FTBFS bugs connected with this proposal, maybe with pagure ticket
to allow discussion.
*** Solutions to most common errors should be gathered and published

* Release engineering: TICKET_TBD (a check of an impact with Release
Engineering is needed)
** mass rebuild will be required for this change

* Policies and guidelines: how to deal with build failures, eventually
how to use some jdk17 specific build features will be provided

* Trademark approval: N/A (not needed for this Change)


== Upgrade/compatibility impact ==
Once the change is implemented properly, the update should be flawless
and seamless


== How To Test ==
* only JDK 21 should remain the only system JDK after installing base
javastack on clean system
* the JDK 8, JDK 11, JDK 17, JDK 21 and java-latest-openjd can
co-exist on one system
* JDK 21 will be selected by default and will run most of the base java stack


== User Experience ==
* Standard user should be still be able to use java stack without even
noticing the change.
* Standard developer should still be able develop any java application
comfortably
* Standard packager will not suffer to much, and should be able to
pack any java application for fedora


== Dependencies ==
Around 2000 packages will need attendance
 $ repoquery -q --whatrequires java-headless |wc -l
 736
 $ repoquery -q --whatrequires java | wc -l
 41
 $ repoquery -q --whatrequires java-devel | wc -l
 13
 $ repoquery -q --whatrequires java-1.8.0-openjdk-headless |wc -l
 653
 $ repoquery -q --whatrequires java-1.8.0-openjdk  | wc -l
 8
 $ repoquery -q --whatrequires java-1.8.0-openjdk-devel  | wc -l
 4
 $ repoquery -q --whatrequires java-11-openjdk-headless |wc -l
 663
 $ repoquery -q --whatrequires java-11-openjdk  | wc -l
 8
 $ repoquery -q --whatrequires java-11-openjdk-devel  | wc -l
 5
 $ repoquery -q --whatrequires java-17-openjdk-headless |wc -l
 757
 $ repoquery -q --whatrequires java-17-openjdk |wc -l
 55
 $ repoquery -q --whatrequires java-17-openjdk-devel |wc -l
 20

with src repos on, build time depndnecies:
 set +x ;echo "dont forget to enable all (correct fedora,
fedotra-testing, fedora modules) SOURCE repos (sections in .repo
files)!" ; for x in ant maven-local maven mvn xmvn java-headless java
java-devel java-1.8.0-openjdk-headless java-1.8.0-openjdk
java-1.8.0-openjdk-devel java-11-openjdk-headless   java-11-openjdk
java-11-openjdk-devel ; do for y in ""  "--arch src"  ;do set -x ;
repoquery $y -q --whatrequires $x  |wc -l ; set +x ; done; done
 dont forget to enable all (correct fedora, fedotra-testing, fedora
modules) SOURCE repos (sections in .repo files)
 + repoquery --arch src -q --whatrequires ant
 152
 + repoquery --arch src -q --whatrequires maven-local
 401
 + repoquery --arch src -q --whatrequires maven
 4
 + repoquery --arch src -q --whatrequires mvn
 0
 + repoquery --arch src -q --whatrequires xmvn
 0
 + repoquery --arch src -q --whatrequires java-headless
 5
 + repoquery --arch src -q --whatrequires java
 0
 + repoquery --arch src -q --whatrequires java-devel
 207
 + repoquery --arch src -q --whatrequires java-1.8.0-openjdk-headless
 6
 + repoquery --arch src -q --whatrequires java-1.8.0-openjdk
 0
 + repoquery --arch src -q --whatrequires java-1.8.0-openjdk-devel
 19
 + repoquery --arch src -q --whatrequires java-11-openjdk-headless
 0
 + repoquery --arch src -q --whatrequires java-11-openjdk
 0
 + repoquery --arch src -q --whatrequires java-11-openjdk-devel
 15


Packages needing major work will be
* java-17-openjdk
* java-21-openjdk
* javapackages-tools
* maybe maven base


== Contingency Plan ==
* If the mass rebuild, after the changes are applied, breaks too many
packages, or some crucial component will be unfixable, JDK 17 must be
restored back to the position of system JDK.

* Contingency mechanism: Return jdk8 as system jdk and mass rebuild
again. Note, that this may be very hard, because during build of
packages by jdk8, by jdk11 built dependencies will be picekd up, so
build will fail. Maybe several iterations of mass rebuild will be
needed.
* Contingency deadline: Announce release blocking deliverables     Tue
2022-02-01     Tue 2022-02-01     0 (8days before branching, 22 before
beta freeze)
* Blocks release? Yes
* Blocks product? N/A
* In general, going back will be, in my opinion, impossible. Once the
decision is taken, java stack should be fixed, and where it can not be
fixed, it has to migrate to compat packages, or bundled-dependencies
packages, or be orphaned.
=== side tag ===
https://fedoraproject.org/wiki/Package_update_HOWTO#Creating_a_side-tag
* for these changes, Fedora has technology known as side tag
* I do not have experience with it, but it is making the contingency
plan much smoother
* it is an approach, which will be used first

== Documentation ==
* oracle 21 release notes:
https://www.oracle.com/java/technologies/javase/21-relnote-issues.html
* openjdk21 jeps: https://openjdk.java.net/projects/jdk/21/
https://openjdk.java.net/projects/jdk/20/
https://openjdk.java.net/projects/jdk/19/
https://openjdk.java.net/projects/jdk/18/
* oracle migration guide
https://docs.oracle.com/en/java/javase/21/migrate/index.html
=== common issues packagers can face and gathered solutions ===
Contacts: ask on devel@lists.fedoraproject.org or
java-de...@lists.fedoraproject.org or directly to me
pmik...@redhat.com
Threads of "F40 system wide change, java-21-openjdk as a system JDK"

Major database can be browsing of closed bugs of blockers of
https://bugzilla.redhat.com/show_bug.cgi?id=TODO ; unluckily, when it
was analysed, it was not summarised up (that would actually double the
work)
==== My package can not work with JDK 21 ====
No program can say, that it does not support JDK 21, because any
javac/java application can be remade to work with JDK 21 - see
https://jvanek.fedorapeople.org/devconf/2017/portingjavaInternalToJdk9/portingOfItwToJdk9-II.pdf
(really all except package split over modules, which is impossible)

Now above mentioned approaches are indeed *hacked*, and I discourage
everybody to do so. The upstream should be moved to jdk21, and not
much excuses are around to support to not to do so. If you package is
really bound to JDK 17, you can move to the version-full requires:
  BuildRequires: java-17-openjdk(-devel)
and
  Requires: java-17-openjdk(-headless).

In addition, '''if  you work with maven/ant or similar builders, you
must set export JAVA_HOME=/usr/lib/jvm/java-11
-openjdk before calling
it.''' javapackage-tools and comp are made to accept it.

However there is a trap - the packages you are depending on.  Once
some of your dependencies will be compiled
with --target > 8, you are doomed, and you have to bundle it or create
its compat version. By doing
so you can easily end up in dependency hell.

Please, try to avoid this as much as possible!
===== Intermediate step build with java-17-openjdk-devel and run with
java (that means any sytem java, eg java-21-openjdk) =====
Some projects support JDK21 for runtime, but not for compile time.
 Buildrequires: java-17-openjdk-devel
 ...
 Requires: java(-headless)
 ...
 %build
 ...
  export JAVA_HOME=/usr/lib/jvm/java-17-openjdk
 ...

Should work for a while. See the "My package can not work with jdk11" section

==== My package is not in your copr! ====
If your package is not listed in the copr rebuild repo, I can see two causes
* You have very indirect BR on java.
** Solution
** Email me (pmik...@redhat.com) or ping me (pmikova), I will gladly
add you package(s)
* You have exact requires on java-11-openjdk(-devel)
** Solution
** Unless you have good reason, you are actually breaking packaging
guidelines. Switch to java-devel. Once done, again let me know and I
will gladly add your package
** If you can't, then you most likely can not bump to jdk17, and you
will live with jdk11 until it dies,

==== Wrong source/target version ====
maven
 [ERROR] Source option 1.3 is no longer supported. Use 7 or later.
 [ERROR] Target option 1.3 is no longer supported. Use 1.7 or later.
ant
 -do-compile:
     [mkdir] Created dir: /builddir/build/BUILD/jpanoramamaker-5/build/empty
     [javac] Compiling 45 source files to
/builddir/build/BUILD/jpanoramamaker-5/build/classes
     [javac] warning: [options] bootstrap class path not set in
conjunction with -source 5
     [javac] error: Source option 5 is no longer supported. Use 7 or later.
     [javac] error: Target option 1.5 is no longer supported. Use 1.7 or later.
 BUILD FAILED
* Solution
** Your javac is run with wrong source/tag parameters.
[https://duckduckgo.com/?t=ffsb&q=javac+source+target&ia=web net
search will give you quick answer]
** Fixes are:
*** 
[https://src.fedoraproject.org/rpms/CardManager/blob/2d6e0f1e3d23d864c1ed0b20f6076fa4c9a15c21/f/bumpJdk.patch
example patch for netbeans generated ant]

== Release Notes ==


-- 
Aoife Moloney

Fedora Operations Architect

Fedora Project

Matrix: @amoloney:fedora.im

IRC: amoloney
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