A Ready Solution for Unix
Lucky you if you have to use both Java 7 and 8 for different projects on the same dev box. I can totally relate the pain.
Initially, I was hoping brew would be able to magically sort out this problem for me. And boy, how naive was I. After few digging, it is not hard to find out brew is surely not the tool for this kind of job.
This is how jenv comes to the rescue. Obviously,
jenv is a Java version managing tool. How
jenv works is by setting up a shim in your home directory, and by adding the following lines to your
.bash_profile, it then takes over and finds the right Java version to use globally or in a specific directory.
Of course, you need to have different Java versions installed, and this is something brew cask will happily handle.
The next important thing is to make sure
jenv is aware of the JDKs installed by adding them to
jenv. The Java versions are normally installed under
jenv is in fact really easy and pleasant with command line.
This seems like a happy ever after love story, but think again, is it though?
The likelihood is the project is now configured to use right Java version, but other tools, such as Maven, may disagree. The reason being as
jenvshim takes over
.bash_profile, it does not physically reconfigure Java version installed in
/usr/bin. This will cause a hell lot of confusion while the project is configured to use one version of Java, yet Maven uses another version of Java by default.
There are different approaches to solving this problem, but rather than living with a tool I have no extended understanding of (which has in fact screwed me over more than once), I came up with a home grown solution.
A Home Grown Solution for Unix
Like I mentioned before, the downside of
jenv is that the default version of Java remains unchanged, which causes lots of confusion.
To tackle this problem, my plan is to change default Java environment. The default Java executables configured in
/usr/binare nothing but symlinks, which means despite the fact that they should remain the same (if you want anything to work at all) on the surface, by pointing the executables to the version I want can archive the Java version switching just the same.
To make this work, first of all, you need to install different Java versions needed through our best friend
brew cask. Then, replace all the current Java binaries in
/usr/bin with the target version.
Do remember to check your Java version to confirm the great success.
For whoever is not confident of what they are doing, I’d encourage you to take a copy of existing configs before trashing them.
As for the lazy ones, you know I must have a script to do this kind of dirty work. Yes, you are right. But also bear in mind, I have only come so far to make the script work for switching between Java 7 and 8 on a Mac with the listed Java versions installed.
After going through my solution, I am sure everyone would be able to create a version tailored to their systems.
One last tip I would give is: make sure Java version to use is compatible with the tools. I have colleagues trying to configure Maven 3.2+ to use Java 1.6, and I just can’t stress enough how big a disaster that is.
A Piece of Cake in Linux
Comparing to Unix, switching Java versions (OpenJDK) on Ubuntu 14.04 is like walking in the park.
It is quite unlikely, but if for any odds the package is not available, try running
sudo add-apt-repository ppa:openjdk-r/ppa first.
After all, the solution is solid and widely used by the community, so really, don’t try to be creative unless you are really bored.