Installer doesn't actually install

[inso99]

I'm having trouble installing this package via Ubuntu Software on Ubuntu 22.04/x64.

The installer completes, and everything seems ok in the Ubuntu Software Centre (no issues during installation, says "installed" afterwards).

But then when I run the command:
sudo update-alternatives --config java
no OpenJDK 21 shows up, just the previous versions already installed.

I try to restart the machine and run the same command, but still no OpenJDK 21 to be seen.

There is a user review in Ubuntu Software Center going by the nickname "bdsm" that said back in 25th of August 23 "kya bhai...! Launch hi nahi ho raha tera application", which I found is hindi translates to "What's up bro...! Your application is not launching", indicating that this is not a new problem, and that it has existed for users since at least 25th of August, meaning before OpenJDK 21 was released, ie. also affecting previous releases.

[jgneff]

But then when I run the command: sudo update-alternatives --config java no OpenJDK 21 shows up, just the previous versions already installed.

That's correct. The update-alternatives command is for Debian packages and does not work for confined Snap packages. The OpenJDK Snap package works differently than the normal openjdk-17-jdk Debian package, for example.

Please see the Usage section of the README file in the package repository for information on running the OpenJDK Snap package or configuring it for your development environment. Note that the README provides two ways to use the OpenJDK snap:

1. as a strictly confined package that is limited in its access to your system, or
2. as an unconfined development kit that runs with full access to your system.

For the first option, you can set up your environment by sourcing the openjdk command (with the dot or . command), as shown below:

$ java --version
openjdk 17.0.8.1 2023-08-24
OpenJDK Runtime Environment (build 17.0.8.1+1-Ubuntu-0ubuntu122.04)
OpenJDK 64-Bit Server VM (build 17.0.8.1+1-Ubuntu-0ubuntu122.04, mixed mode, sharing)
$ . $(openjdk)
$ java --version
openjdk 21.0.1 2023-10-17
OpenJDK Runtime Environment (build 21.0.1+12-snap)
OpenJDK 64-Bit Server VM (build 21.0.1+12-snap, mixed mode, sharing)

If you're running Ubuntu 18.04 or later, you can use the second option by defining the JAVA_HOME environment variable and optionally adding it to your PATH variable:

$ java --version
openjdk 17.0.8.1 2023-08-24
OpenJDK Runtime Environment (build 17.0.8.1+1-Ubuntu-0ubuntu122.04)
OpenJDK 64-Bit Server VM (build 17.0.8.1+1-Ubuntu-0ubuntu122.04, mixed mode, sharing)
$ export JAVA_HOME=/snap/openjdk/current/jdk
$ export PATH=$JAVA_HOME/bin:$PATH
$ java --version
openjdk 21.0.1 2023-10-17
OpenJDK Runtime Environment (build 21.0.1+12-snap)
OpenJDK 64-Bit Server VM (build 21.0.1+12-snap, mixed mode, sharing)

These steps are documented in the README file, which is linked from the OpenJDK Snap package description in the Snap Store.

[jgneff]

Actually, it turns out you can add the JDK tools in the OpenJDK Snap package to your system alternatives! It's a tedious process, though, if you're doing it manually for all of the tools in the JDK:

$ ls /snap/openjdk/current/jdk/bin
jar        javap      jdeps   jlink     jrunscript  jwebserver
jarsigner  jcmd       jfr     jmap      jshell      keytool
java       jconsole   jhsdb   jmod      jstack      rmiregistry
javac      jdb        jimage  jpackage  jstat       serialver
javadoc    jdeprscan  jinfo   jps       jstatd

You would need to run a command like the following for each of the tools:

$ sudo update-alternatives \
    --install /usr/bin/java java /snap/openjdk/current/jdk/bin/java 2101 \
    --slave /usr/share/man/man1/java.1 java.1 /snap/openjdk/current/jdk/man/man1/java.1

You don't need the --slave option, but that option also sets up the manual pages of the tool for the man command. After running the command, the java tool is set up as you wanted:

$ update-alternatives --config java
There are 3 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                         Priority   Status
------------------------------------------------------------
* 0            /snap/openjdk/current/jdk/bin/java            2101      auto mode
  1            /snap/openjdk/current/jdk/bin/java            2101      manual mode
  2            /usr/lib/jvm/java-11-openjdk-amd64/bin/java   1111      manual mode
  3            /usr/lib/jvm/java-17-openjdk-amd64/bin/java   1711      manual mode

Press <enter> to keep the current choice[*], or type selection number:
$ update-alternatives --display java
java - auto mode
  link best version is /snap/openjdk/current/jdk/bin/java
  link currently points to /snap/openjdk/current/jdk/bin/java
  link java is /usr/bin/java
  slave java.1 is /usr/share/man/man1/java.1
  slave java.1.gz is /usr/share/man/man1/java.1.gz
/snap/openjdk/current/jdk/bin/java - priority 2101
  slave java.1: /snap/openjdk/current/jdk/man/man1/java.1
/usr/lib/jvm/java-11-openjdk-amd64/bin/java - priority 1111
  slave java.1.gz: /usr/lib/jvm/java-11-openjdk-amd64/man/man1/java.1.gz
/usr/lib/jvm/java-17-openjdk-amd64/bin/java - priority 1711
  slave java.1.gz: /usr/lib/jvm/java-17-openjdk-amd64/man/man1/java.1.gz

The java tool and man java then point to the OpenJDK Snap package:

$ java --version
openjdk 21.0.1 2023-10-17
OpenJDK Runtime Environment (build 21.0.1+12-snap)
OpenJDK 64-Bit Server VM (build 21.0.1+12-snap, mixed mode, sharing)
$ man -w java
/snap/openjdk/1539/jdk/man/man1/java.1

I can look into adding a command, such as openjdk.install, that runs update-alternatives for each of the JDK tools in the OpenJDK Snap package. An openjdk.remove command could remove all of the OpenJDK Snap alternatives. There's also the command update-java-alternatives, but that seems to be more closely tied to the way that Ubuntu (and Debian) create their own OpenJDK packages. This might work only for Ubuntu and Debian systems, so I would need to look into what Red Hat, Fedora, and other systems do for JDK alternatives.

@inso99 If I can get something like this working well, would you be willing to test it?