Multiple Java Versions

If you use multiple versions of Java in your development environment, perhaps you wished there was a better way to switch from one to the other, instead of remembering to set the JAVA_HOME environment variable.

Forgot to set the JAVA_HOME environment variable? If you use multiple versions of Java in your development environment, perhaps you wished there was a better way to switch from one to the other, instead of remembering to set the JAVA_HOME environment variable. Introducing jEnv:

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jEnv is a command line tool to help you forget how to set the JAVA_HOME environment variable.

Install

In the following sections, we describe the installation procedure of jEnv on Linux and macOS environments.

Linux

Simply clone the jEnv repository from GitHub:

git clone https://github.com/gcuisinier/jenv.git ~/.jenv

macOS

We need the Homebrew package manager for macOS:

/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"

Install jEnv using brew:

brew install jenv

Configure

Update your command line environment with jEnv-specific configuration:

export JAVA_HOME="$HOME/.jenv/versions/`jenv version-name`"
alias jenv_set_java_home='export JAVA_HOME="$HOME/.jenv/versions/`jenv version-name`"'

Next, you'll need to add the JAVA home directory paths to your jEnv environment. To list all the JVM versions and architectures in your environment, run:

/usr/libexec/java_home -V

You may get an output similar to (e.g., on macOS):

Matching Java Virtual Machines (3):
    11.0.1, x86_64:    "OpenJDK 11.0.1"    /Library/Java/JavaVirtualMachines/openjdk-11.0.1.jdk/Contents/Home
    1.8.0_192, x86_64:    "Java SE 8"    /Library/Java/JavaVirtualMachines/jdk1.8.0_192.jdk/Contents/Home
    1.8.0_101, x86_64:    "Java SE 8"    /Library/Java/JavaVirtualMachines/jdk1.8.0_101.jdk/Contents/Home

Based on the JVM list above you may add the JAVA home directory paths to your jEnv environment, e.g.:

jenv add /Library/Java/JavaVirtualMachines/openjdk-11.0.1.jdk/Contents/Home
jenv add /Library/Java/JavaVirtualMachines/jdk1.8.0_192.jdk/Contents/Home

Now your jEnv environment is ready to manage the various JVM versions in your development environment.

jenv versions

The aforementioned command would yield an output similar to:

  system
  1.8
  1.8.0.192
  11.0
  11.0.1
  openjdk64-11.0.1
  oracle64-1.8.0.192

You can set specific versions of JVM per workspace directory. Assuming you have a directory with a Java code base requiring JVM 1.8, you can switch to that directory and set the JVM version of choice, e.g.:

jenv local 1.8

You may still choose a default global version of JVM on your system, e.g., 11:

jenv global 11

Happy Java coding!

Resources

http://www.jenv.be/

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