Linux Alternatives and Oracle Java

If, like me, you prefer to run the Oracle version of Java on your Linux machine as the default JDK, you will often find that the Linux distro will have other ideas.  Fedora for example has a number of Java based applications as part of the distribution which will include a dependency on the OpenJDK.  When the distro installs OpenJDK is will generally be setup as the default for executing the various Java binaries (e.g. 'java', 'javac').  However, the team at Redhat built a system called alternatives which maintains a set of symbolic links that allows the user to switch between multiple implementations of a package the supports the same functionality.  I've managed to understand enough about the alternatives package that I can now easily switch between the Oracle JDK and the OpenJDK.

Alternatives has the notion of master and slave configurations.  The way that the OpenJDK sets up the alternatives is that it uses 2 masters 'java' for the runtime (JRE) and 'javac' for the development tools (JDK).  To set the Oracle JDK in a similar way you need a script like this:

	#!/bin/bash
	LINKDIR=/usr/bin
	JHOME=/usr/java/latest
	JREDIR=$JHOME/jre/bin
	JDKDIR=$JHOME/bin
	sudo alternatives --install $LINKDIR/java java$JREDIR/java 20000 \
	--slave $LINKDIR/keytool keytool$JREDIR/keytool \
	--slave $LINKDIR/orbd orbd$JREDIR/orbd \
	--slave $LINKDIR/pack200 pack200$JREDIR/pack200 \
	--slave $LINKDIR/rmid rmid$JREDIR/rmid \
	--slave $LINKDIR/rmiregistry rmiregistry$JREDIR/rmiregistry \
	--slave $LINKDIR/servertool servertool$JREDIR/servertool \
	--slave $LINKDIR/tnameserv tnameserv$JREDIR/tnameserv \
	--slave $LINKDIR/unpack200 unpack200$JREDIR/unpack200 \
	--slave $LINKDIR/jcontrol jcontrol$JREDIR/jcontrol \
	--slave $LINKDIR/javaws javaws$JREDIR/javaws
	sudo alternatives --install $LINKDIR/javac javac$JDKDIR/javac 20000 \
	--slave $LINKDIR/appletviewer appletviewer$JDKDIR/appletviewer \
	--slave $LINKDIR/apt apt$JDKDIR/apt \
	--slave $LINKDIR/extcheck extcheck$JDKDIR/extcheck \
	--slave $LINKDIR/idlj idlj$JDKDIR/idlj \
	--slave $LINKDIR/jar jar$JDKDIR/jar \
	--slave $LINKDIR/jarsigner jarsigner$JDKDIR/jarsigner \
	--slave $LINKDIR/javadoc javadoc$JDKDIR/javadoc \
	--slave $LINKDIR/javah javah$JDKDIR/javah \
	--slave $LINKDIR/javap javap$JDKDIR/javap \
	--slave $LINKDIR/jcmd jcmd$JDKDIR/jcmd \
	--slave $LINKDIR/jconsole jconsole$JDKDIR/jconsole \
	--slave $LINKDIR/jdb jdb$JDKDIR/jdb \
	--slave $LINKDIR/jhat jhat$JDKDIR/jhat \
	--slave $LINKDIR/jinfo jinfo$JDKDIR/jinfo \
	--slave $LINKDIR/jmap jmap$JDKDIR/jmap \
	--slave $LINKDIR/jps jps$JDKDIR/jps \
	--slave $LINKDIR/jrunscript jrunscript$JDKDIR/jrunscript \
	--slave $LINKDIR/jsadebugd jsadebugd$JDKDIR/jsadebugd \
	--slave $LINKDIR/jstack jstack$JDKDIR/jstack \
	--slave $LINKDIR/jstat jstat$JDKDIR/jstat \
	--slave $LINKDIR/jstatd jstatd$JDKDIR/jstatd \
	--slave $LINKDIR/native2ascii native2ascii$JDKDIR/native2ascii \
	--slave $LINKDIR/policytool policytool$JDKDIR/policytool \
	--slave $LINKDIR/rmic rmic$JDKDIR/rmic \
	--slave $LINKDIR/schemagen schemagen$JDKDIR/schemagen \
	--slave $LINKDIR/serialver serialver$JDKDIR/serialver \
	--slave $LINKDIR/wsgen wsgen$JDKDIR/wsgen \
	--slave $LINKDIR/wsimport wsimport$JDKDIR/wsimport \
	--slave $LINKDIR/xjc xjc$JDKDIR/xjc
	sudo alternatives --install /usr/lib64/mozilla/plugins/libjavaplugin.so libjavaplugin.so.x86_64 $JHOME/jre/lib/amd64/libnpjp2.so 20000

view raw java-alternatives-install.sh hosted with ❤ by GitHub

Once you have run that script then you can configure the JRE and JDK of your choice:

$ sudo alternatives --config java

Which will provide a prompt allowing you to choose your desired JRE

There is 2 program that provides 'java'.

  Selection    Command
-----------------------------------------------
*  1           /usr/lib/jvm/java-1.7.0-openjdk-1.7.0.60...
 + 2           /usr/java/latest/jre/bin/java

Enter to keep the current selection[+], or type selection number:

And run the same thing for the JDK:

$ sudo alternatives --config javac