Ubuntu 10.04 : Install and set Sun JDK as default

 
Since ubuntu 10.04, Sun JDK has been dropped and replaced by openjdk.
Literally replaced, ie : Sun JDK remove, openjdk installed.

This is performed during the upgrade without explicitly asking you for your consent...
which is quite ugly... After the upgrade, my tomcat was not working anymore...

Anyway, in order to install Sun JDK back you just have to :

vi /etc/apt/sources.list

and check if the following line is present :

deb http://archive.canonical.com/ lucid partner

if not, add it at the end of the file.
then run

sudo aptitude update

to get the package list from the new repo.
and then run :

sudo aptitude install sun-java6-jdk

but after that, if you run java -version, it's still the openjdk version.

thomas@daisybox:/usr/lib/jvm/java-6-sun$ java -version
java version "1.6.0_18"
OpenJDK Runtime Environment (IcedTea6 1.8) (6b18-1.8-0ubuntu1)
OpenJDK 64-Bit Server VM (build 14.0-b16, mixed mode)

thomas@daisybox:/usr/lib/jvm/java-6-sun$ which java
/usr/bin/java
thomas@daisybox:/usr/lib/jvm/java-6-sun$ ll /usr/bin/java
lrwxrwxrwx 1 root root 22 2010-05-11 23:44 /usr/bin/java -> /etc/alternatives/java
thomas@daisybox:/usr/lib/jvm/java-6-sun$ ll /etc/alternatives/java
lrwxrwxrwx 1 root root 40 2010-05-11 23:44 /etc/alternatives/java -> /usr/lib/jvm/java-6-openjdk/jre/bin/java

You could try to remove openjdk, but you'll hit some annoying dependency issue.

Instead of removing you can configure the system to default to Sun JDK

thomas@daisybox:~$ sudo update-alternatives --config java
There are 2 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                      Priority   Status
------------------------------------------------------------
* 0            /usr/lib/jvm/java-6-openjdk/jre/bin/java   1061      auto mode
  1            /usr/lib/jvm/java-6-openjdk/jre/bin/java   1061      manual mode
  2            /usr/lib/jvm/java-6-sun/jre/bin/java       63        manual mode

Press enter to keep the current choice[*], or type selection number: 2
update-alternatives: using /usr/lib/jvm/java-6-sun/jre/bin/java to provide /usr/bin/java (java) in manual mode.

thomas@daisybox:/usr/lib/jvm/java-6-sun$ ll /etc/alternatives/java
lrwxrwxrwx 1 root root 36 2010-05-11 23:48 /etc/alternatives/java -> /usr/lib/jvm/java-6-sun/jre/bin/java

thomas@daisybox:~$ java -version
java version "1.6.0_20"
Java(TM) SE Runtime Environment (build 1.6.0_20-b02)
Java HotSpot(TM) 64-Bit Server VM (build 16.3-b01, mixed mode)

Or more directly like "Daniel Bos" suggest in the comments :

sudo update-java-alternatives -s java-6-sun

_{image taken from : http://www.sucka.net/2010/04/jdk-linux-update-script/}