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I have been trying to figure out the best way to run OpenJDK Java Runtime as default Java for my Fedora box and use Oracle JDK 6 for Android development namely for running Android SDK Manager, Android Studio and Eclipse from Android Bundle.

I installed OpenJDK Java Runtime from the Fedora repository which has setup alternatives as follow.

[donnie@fedora ~]$ alternatives --list | grep java
jre_openjdk             auto    /usr/lib/jvm/java-1.7.0-openjdk-1.7.0.60-2.4.5.1.fc20.x86_64/jre
jre_1.7.0               auto    /usr/lib/jvm/java-1.7.0-openjdk-1.7.0.60-2.4.5.1.fc20.x86_64/jre
java                    auto    /usr/lib/jvm/java-1.7.0-openjdk-1.7.0.60-2.4.5.1.fc20.x86_64/jre/bin/java
libjavaplugin.so.x86_64 auto    /usr/lib64/IcedTeaPlugin.so

I have installed the Oracle JDK 6 using the rpm provided by Oracle.

I could make Android Bundle and Studio make use of JAVA_HOME to run under Oracle JDK by sticking following in .bashrc.

export JAVA_HOME=/usr/java/jdk1.6.0_45/
export PATH=$JAVA_HOME/bin:$PATH

I noticed that Chrome still uses OpenJDK (as I still need to link the plugin).

What are the difference between JAVA_HOME and using alternatives?

Gilles 'SO- stop being evil'
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Sudhir Singh Khanger
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1 Answers1

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Alternatives

Alternatives is a tool that will manage the locations of the installed software using links under the control of the alternatives tool.

These links are ultimately managed under /etc/alternatives with intermediate links created under a directory in $PATH, typically /usr/bin.

Example

$ ls -l /usr/bin/java
lrwxrwxrwx. 1 root root 22 Feb 24 17:36 /usr/bin/java -> /etc/alternatives/java

$ ls -l /etc/alternatives/java
lrwxrwxrwx. 1 root root 73 Feb 24 17:36 /etc/alternatives/java -> /usr/lib/jvm/java-1.7.0-openjdk-1.7.0.60-2.4.5.0.fc19.x86_64/jre/bin/java

$JAVA_HOME

$JAVA_HOME is where software can be told to look through the use of an environment variable. Adding it to the $PATH simply adds the executables present in $JAVA_HOME/bin to your $PATH. This is sometimes necessary for certain applications.

The 2 mechanisms are related but can be used together or independent of each other, it really depends on the Java application which mechanism is preferable.

What I do

I typically use $JAVA_HOME for some GUI applications, but in general use it only for server installations that make use of Jetty, Tomcat, or JBOSS, for example.

For these installations I'll still use alternatives to manage the Java installations prior to setting the $JAVA_HOME. I like doing it this way in cases where I might need to have multiple installations of Java.

Alternatives does allow you to have certain tools use one installation of Java while other tools use a completely different one.

References

slm
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  • The giveaway is that with alternatives I can use different components of Java. For example, Alternatives can set `java` and `javac` from different JDKs on the other hand `JAVA_HOME=JAVALOCATION` would point `java`, `javac`, and `javaws` to `java`, `javac` and `javaws` in `JAVALOCATION`, respectively. – Sudhir Singh Khanger Apr 07 '14 at 05:49
  • The reason I asked this [question](http://goo.gl/qmcqEx) was how can I use OpenJDK as default Java Runtime and make Android Studio, Eclipse and SDK Manager use Oracle JDK. I can run those three programs under Oracle JDK by hard editing their startup scripts which might get broken if they are updated. I was looking for something more generic like `STUDIO_JDK`, that I can add to `~/.profile` or `~/.bashrc`, that is used by Android Studio for picking up JDK but I think Android Bundle (Eclipse and SDK Manager) won't honor that. – Sudhir Singh Khanger Apr 07 '14 at 05:56
  • @donniezazen - yeah `STUDIO_JDK` is a custom thing. I would use alternatives for those tools and set `JAVA_HOME`to the path under `/usr/bin` which is managed by `alternatives`. When upgrades are performed, changing `alternatives` is all that's required. – slm Apr 07 '14 at 11:45
  • I am not sure what you are proposing. Point both `alternatives` and `JAVA_HOME` to say `/usr/bin/java`. Also it seems like `JAVA_HOME` overrides `alternatives`. – Sudhir Singh Khanger Apr 07 '14 at 12:23
  • @donniezazen - yes use alternatives to manage your JAVA installs and then use `JAVA_HOME`, pointing it to `/usr/bin`. You're correct, `JAVA_HOME` can operate independently from `alternatives`. – slm Apr 07 '14 at 13:08
  • What are we trying to accomplish by pointing `JAVA_HOME` to `/usr/bin`? `/usr/bin` contains java binaries managed by `alternatives`. `JAVA_HOME` would be redundant in the case you are suggesting. And either `OpenJDK` or `Oracle JDK` will become system default. Whereas I want OpenJDK as default and Oracle JDK for Android development. – Sudhir Singh Khanger Apr 07 '14 at 13:30
  • @donniezazen - yes but some applications will only utilize Java through `JAVA_HOME`. Often times this is app servers such as JBoss or Jetty. They have stop/start service scripts that need `JAVA_HOME` defined. GUI apps too will often times need `JAVA_HOME`. It's hit or miss which fall into this category so it's often easier to just define it up front for the box. – slm Apr 07 '14 at 13:37
  • Thanks @slm you have been very helpful. It seems like there is no generic way to achieve what i want to do. I think i will go ahead and use OpenJDK's Icedtea for chrome for security and Oracle JDK as system default as Android development takes precedence. – Sudhir Singh Khanger Apr 07 '14 at 13:50