Gentoo Java Guide
1. Installing a JDK/JRE
Gentoo provides numerous JDKs and JREs. The default is the Blackdown JDK/JRE
pair, as it is freely (beer) available without any registration fuss.
As kaffe becomes a JRE/JDK drop-in replacement, that will most likely become our
Both the Sun JDK/JRE and the IBM JDK/JRE are generally faster, but getting them
is a bit more work, as you are required to read and accept their license before
downloading (IBM additionally requires you to register).
Our ebuilds for the Sun and IBM JDK/JREs will notify you of where to go to
Installing the Sun/IBM JDK/JREs
If you run emerge sun-jdk-1.3.1 or emerge ibm-jdk-1.3.1, you will
be notified that you are required to download the actual tarballs yourself. This
has to do with license restrictions for the Sun JDK/JRE (online click-wrap
license) and registration issues with the IBM JDK/JRE.
There is also a sun-jdk-1.4.0, but not all packages work nicely with Java 1.4,
so you're on your own if you use the 1.4.0 JDK.
You should download the indicated file(s) into
/usr/portage/distfiles. Once that is done, you can rerun the emerge
command, then the JDK/JRE will be installed properly into /opt.
2. Configuring your JDK/JRE
Gentoo has the ability to have multiple JDKs and JREs installed without them
Using the java-config tool, you can set the system-wide default if you
have root access. Users can also use java-config to set up their own
personal default, that is different from the system-wide default.
Setting a default JDK/JRE
Running the command java-config --list-available-vms will give you a list
of all available JREs and JDKs on your system, thus:
Code Listing 2.1: Listing available VMs
# java-config --list-available-vms
[blackdown-jdk-1.3.1] Blackdown JDK 1.3.1 (/etc/env.d/java/20blackdown-jdk-1.3.1)
[blackdown-jre-1.3.1] Blackdown JRE 1.3.1 (/etc/env.d/java/20blackdown-jre-1.3.1)
[ibm-jdk-1.3.0] IBM JDK 1.3.0 (/etc/env.d/java/20ibm-jdk-1.3.0)
[ibm-jdk-1.3.1] IBM JDK 1.3.1 (/etc/env.d/java/20ibm-jdk-1.3.1)
[ibm-jre-1.3.1] IBM JRE 1.3.1 (/etc/env.d/java/20ibm-jre-1.3.1)
[sun-jdk-1.4.0] Sun JDK 1.4.0 (/etc/env.d/java/20sun-jdk-1.4.0)
The name in the brackets "" is the handle or ID for that
particular VM. You use pass that ID to java-config --set-system-vm, thus:
Code Listing 2.2: Setting the System VM
# java-config --set-system-vm=ibm-jdk-1.3.1
Now using IBM JDK 1.3.1 (/etc/env.d/java/20ibm-jdk-1.3.1)
You will have to be root to run --set-system-vm.
Once you have issued java-config --set-system-vm with a particular VM ID,
you will need to regenerate your /etc/profile.env, thus:
Code Listing 2.3: Regenerating /etc/profile.env
After this, you will either want to relogin, or resource
/etc/profile into your environment.
As a regular user, you can use java-config --set-user-vm, which will
create $HOME/.gentoo/java-env with all required env vars. You would
normally source this from your shell's startup script
($HOME/.zshenv in my case).
Setting a default CLASSPATH
java-config can also be used to set a system-wide default CLASSPATH, and
of course a user-specific default CLASSPATH.
First you want to list available java libraries that might be interesting to put
in your CLASSPATH, thus:
Code Listing 2.4: Listing classes
# java-config --list-available-packages
[ant] No description (/usr/share/ant/classpath.env)
[java-gnome] No description (/usr/share/java-gnome/classpath.env)
[java-gtk] No description (/usr/share/java-gtk/classpath.env)
[log4j] "" (/usr/share/log4j/package.env)
None of these packages have a proper description. That is something that will be
implemented in the not-so-distant future.
Again, the name in brackets "" are the IDs that you have to pass
to java-config --set-system-classpath, thus:
Code Listing 2.5: Setting classpaths
# java-config --set-system-classpath=log4j,java-gtk,java-gnome
The current directory (.) will not be part of the system classpath, as that
should be added in root's login profile.
Again, you will want to run env-update to update your system's
environment, and you might also want to relogin or resource the
For users, java-config --set-user-classpath will create
$HOME/.gentoo/java-env-classpath, which is automatically included
3. Additional resources
- java-config man page
- java-config --help
- The /usr/bin/java-config script itself
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