switching Java version

in

I've been switching between Mac and Ubuntu, and between Java 6 and 7 lately.
This is a memo of how to switch Java versions on both Mac and Ubuntu.

Update: Yoshida-san told me about this thing called jEnv, which does all this.

Zshrc

Here's one way of loading different shell files depending on the OS:

## basic
[ -f $HOME/dotfiles/zshrc.basic ] && source $HOME/dotfiles/zshrc.basic

## aliases
[ -f $HOME/dotfiles/zshrc.alias ] && source $HOME/dotfiles/zshrc.alias

case "${OSTYPE}" in
# MacOSX
darwin*)
  [ -f $HOME/dotfiles/zshrc.osx ] && source $HOME/dotfiles/zshrc.osx
  ;;
# Linux
linux*)
  [ -f $HOME/dotfiles/zshrc.linux ] && source $HOME/dotfiles/zshrc.linux
  ;;
esac

## color
[ -f $HOME/dotfiles/zshrc.color ] && source $HOME/dotfiles/zshrc.color

environment variables

In zshrc.osx and zshrc.linux respectively you can define environment variables for Java 6, 7, and 8. Here's for Mac:

export JAVA_1_6_HOME=`/usr/libexec/java_home -v 1.6`
export JAVA_1_7_HOME=`/usr/libexec/java_home -v 1.7`
export JAVA_1_8_HOME=`/usr/libexec/java_home -v 1.8`

and here's for Ubuntu:

export JAVA_1_6_HOME="/usr/lib/jvm/java-1.6.0-openjdk-amd64"
export JAVA_1_7_HOME="/usr/lib/jvm/java-1.7.0-openjdk-amd64"
export JAVA_1_8_HOME="/usr/lib/jvm/java-8-oracle"

aliases

To use the environment variables for a duration of one shell command, we can use env command. Define these in zshrc.alias.

alias jdk6='env JAVA_HOME=$JAVA_1_6_HOME PATH=$JAVA_1_6_HOME/bin:"$PATH" JDK_SET="1"'
alias jdk7='env JAVA_HOME=$JAVA_1_7_HOME PATH=$JAVA_1_7_HOME/bin:"$PATH" JDK_SET="1"'
alias jdk8='env JAVA_HOME=$JAVA_1_8_HOME PATH=$JAVA_1_8_HOME/bin:"$PATH" JDK_SET="1"'

Here's how to use this:

$ java -version
java version "1.8.0_40-ea"
Java(TM) SE Runtime Environment (build 1.8.0_40-ea-b23)
Java HotSpot(TM) 64-Bit Server VM (build 25.40-b25, mixed mode)
$ echo $JAVA_HOME
/Library/Java/JavaVirtualMachines/jdk1.8.0_40.jdk/Contents/Home
$ jdk6 java -version
java version "1.6.0_65"
Java(TM) SE Runtime Environment (build 1.6.0_65-b14-466.1-11M4716)
Java HotSpot(TM) 64-Bit Server VM (build 20.65-b04-466.1, mixed mode)

For the duration of the command jdk6 COMMAND will run using JDK 6. If you want it for the duration of the session, you start a new shell as follows:

$ jdk6 zsh
$ java -version
java version "1.6.0_65"
Java(TM) SE Runtime Environment (build 1.6.0_65-b14-466.1-11M4716)
Java HotSpot(TM) 64-Bit Server VM (build 20.65-b04-466.1, mixed mode)

If you've noticed that I'm setting JDK_SET variable, you'll see why soon.

system-level Java

You might also be interested in switching the default JDK for the system. For Ubuntu, you can use:

$ update-java-alternatives -l
java-1.6.0-openjdk-amd64 1061 /usr/lib/jvm/java-1.6.0-openjdk-amd64
java-1.7.0-openjdk-amd64 1071 /usr/lib/jvm/java-1.7.0-openjdk-amd64
java-8-oracle 1072 /usr/lib/jvm/java-8-oracle
$ sudo update-java-alternatives -s java-1.7.0-openjdk-amd64

The situation with Mac is weirder. To really change the system-level Java, you would have to find the latest installer and install it last to take effect. If you care only about how java runs in your terminal, the following should work:

if [ -z "$JDK_SET" ]; then
  export JAVA_HOME=`/usr/libexec/java_home -v 1.7`
  export PATH=$JAVA_HOME/bin:$PATH
fi

This checks if $JDK_SET has been set by us, and if not forces JDK 1.7.