[arch-dev-public] JAVA_HOME in systemd

[Guillaume ALAUX]

On 6 February 2013 15:46, Tom Gundersen <teg at jklm.no> wrote:
> On Feb 6, 2013 3:09 PM, "Guillaume ALAUX" <guillaume at archlinux.org> wrote:
>>
>> On 6 February 2013 15:08, Guillaume ALAUX <guillaume at archlinux.org> wrote:
>> > ---------- Forwarded message ----------
>> > From: Leonidas Spyropoulos <artafinde at gmail.com>
>> > Date: 6 February 2013 14:52
>> > Subject: Re: [arch-dev-public] JAVA_HOME in systemd
>> > To: guillaume at archlinux.org
>> >
>> >
>> > On Wed, Feb 6, 2013 at 1:36 PM, Jan Steffens <jan.steffens at gmail.com>
> wrote:
>> >> On Wed, Feb 6, 2013 at 1:58 PM, Gaetan Bisson <bisson at archlinux.org>
> wrote:
>> >>> You can always have each Java runtime provide a different file, and
>> >>> include all of them in each Java service file using
>> >>>
>> >>>         EnvironmentFile=-/path/to/java/runtime/number/one
>> >>>         EnvironmentFile=-/path/to/java/runtime/number/two
>> >>>
>> >>> etc.
>> >>
>> >> You can also pass a wildcard expression, avoiding hardcoding several
> files,
>> >> maybe like this:
>> >>
>> >> EnvironmentFile=-/etc/java-runtime.d/*
>> >> EnvironmentFile=-/etc/java-runtime
>> >>
>> >> Needs testing, but could allow the user to set a default runtime via
> symlink.
>> >>
>> >> Alternatively, just EnvironmentFile=/etc/java-runtime and create this
> symlink
>> >> at post_install of every java-runtime, if it doesn't exist already.
>> >> To be tidy, post_remove then deletes the file if java-runtime.d
>> >> doesn't exist anymore.
>> >
>> > I can't send to mailing list as I am not a dev / TU.
>> > Isn't it possible to detect the JDK on runtime? Getting it from the
>> > java command? (or the javac command)
>> >
>> > --
>> > Caution: breathing may be hazardous to your health.
>> >
>> > #include <stdio.h>
>> > int main(){printf("%s","\x4c\x65\x6f\x6e\x69\x64\x61\x73");}
>>
>> The point is to enable the user to statically set which JRE must be
>> used. Detecting it at each java app runtime would not be ideal.
>>
>> And I'd also rather not have to list all potential JRE in all java
>> systemd files.
>>
>> Creating a symlink at post_install if it does not already exist looks
>> nice to me.
>
> The symlink seems reasonable to me. It would be nice if all the
> distros/upstreams could agree on a scheme though as this does not sound
> Arch/systemd specific.
>
> Cheers,
>
> Tom

Someone [0] proposed a clean/clever solution.

What about a symlink /usr/lib/jvm/default-java pointing to the
required runtime environment? Each Java runtime would need to check if
this link already exists. If not then just create it to point at the
newly installed JRE, if it already exists then just warn the user
about it and how to modify it.

Systemd service files could then use
'Environment=JAVA_HOME=/usr/lib/jvm/default-java' or if they wish use
a specific one.

[0] http://stackoverflow.com/a/663726