Juggling with JDKs on Apple OS X
- by Blueberry Coder
I recently got a shiny new MacBook Pro to help me support our ADF Mobile customers. It is really a wonderful piece of hardware, although I am still adjusting to Apple's peculiar keyboard layout. Did you know, for example, that the « delete » key actually performs a « backspace »? But I disgress... As you may know, ADF Mobile development still requires JDeveloper 11gR2, which in turn runs on Java 6. On the other hand, JDeveloper 12c needs JDK 7. I wanted to install both versions, and wasn't sure how to do it.
If you remember, I explained in a previous blog entry how to install JDeveloper 11gR2 on Apple's OS X. The trick was to use the /usr/libexec/java_home command in order to invoke the proper JDK. In this case, I could have done the same thing; the two JDKs can coexist without any problems, since they install in completely different locations. But I wanted more than just installing JDeveloper. I wanted to be able to select my JDK when using the command line as well. On Windows, this is easy, since I keep all my JDKs in a central location. I simply have to move to the appropriate folder or type the folder name in the command I want to execute. Problem is, on OS X, the paths to the JDKs are... let's say convoluted.
Here is the one for Java 6.
/System/Library/Java/JavaVirtualMachines/1.6.0.jdk/Contents/Home
The Java 7 path is not better, just different.
/Library/Java/JavaVirtualMachines/jdk1.7.0_45.jdk/Contents/Home
Intuitive, isn't it? Clearly, I needed something better...
On OS X, the default command shell is bash. It is possible to configure the shell environment by creating a file named « .profile » in a user's home folder. Thus, I created such a file and put the following inside:
export JAVA_7_HOME=$(/usr/libexec/java_home -v1.7)
export JAVA_6_HOME=$(/usr/libexec/java_home -v1.6)
export JAVA_HOME=$JAVA_7_HOME
alias java6='export JAVA_HOME=$JAVA_6_HOME'
alias java7='export JAVA_HOME=$JAVA_7_HOME'
The first two lines retrieve the current paths for Java 7 and Java 6 and store them in two environment variables. The third line marks Java 7 as the default. The last two lines create command aliases. Thus, when I type java6, the value for JAVA_HOME is set to JAVA_6_HOME, for example.
I now have an environment which works even better than the one I have on Windows, since I can change my active JDK on a whim. Here a sample, fresh from my terminal window.
fdesbien-mac:~ fdesbien$ java6
fdesbien-mac:~ fdesbien$ java -version
java version "1.6.0_65"
Java(TM) SE Runtime Environment (build 1.6.0_65-b14-462-11M4609)
Java HotSpot(TM) 64-Bit Server VM (build 20.65-b04-462, mixed mode)
fdesbien-mac:~ fdesbien$
fdesbien-mac:~ fdesbien$ java7
fdesbien-mac:~ fdesbien$ java -version
java version "1.7.0_45"
Java(TM) SE Runtime Environment (build 1.7.0_45-b18)
Java HotSpot(TM) 64-Bit Server VM (build 24.45-b08, mixed mode)
fdesbien-mac:~ fdesbien$
Et voilà! Maximum flexibility without downsides, just I like it.
