java-home commands fetch and install JVMs. The
java command runs them too.
If a JVM is already installed on your system, the
java command simply calls it, just as if you called it yourself:
$ java -version java version "1.8.0_121" Java(TM) SE Runtime Environment (build 1.8.0_121-b13) Java HotSpot(TM) 64-Bit Server VM (build 25.121-b13, mixed mode) $ cs java -version java version "1.8.0_121" Java(TM) SE Runtime Environment (build 1.8.0_121-b13) Java HotSpot(TM) 64-Bit Server VM (build 25.121-b13, mixed mode)
java-home command prints its base directory, which can look like
$ cs java-home /Library/Java/JavaVirtualMachines/jdk1.8.0_121.jdk/Contents/Home
If no JVM is installed on your system, the default one is automatically downloaded and extracted in the JVM cache, and used. As of writing this, the default JVM is the latest AdoptOpenJDK 8 from the JVM index.
java-home commands accept a JVM name via
--jvm. For example, one can run the
java binary from AdoptOpenJDK 13.0.2 via
$ cs java --jvm adopt:13.0-2 -version openjdk version "13.0.2" 2020-01-14 OpenJDK Runtime Environment AdoptOpenJDK (build 13.0.2+8) OpenJDK 64-Bit Server VM AdoptOpenJDK (build 13.0.2+8, mixed mode, sharing)
The AdoptOpenJDK 13.0.2 JVM is automatically downloaded and extracted on your system if it's not already.
cs java --available lists the JVMs available in the index:
$ cs java --available | grep adopt adopt:1.8.0-172 adopt:1.8.0-181 adopt:1.8.0-192 adopt:1.8.0-202 adopt:1.8.0-212 …
cs java --installed lists the ones currently installed on your system:
$ cs java --installed adopt:1.8.0-242 adopt:1.11.0-6 adopt:1.13.0-2 graalvm:19.3.1 graalvm-java11:19.3.1 openjdk:1.14.0
To list the JVM that can be installed from it, run
$ cs java --available
If needed, that index could be complemented or replaced by an index of our own at some point.
Short JVM names
The full names from the index can be cumbersome to remember and type (
Shorter syntaxes are supported. If the version doesn't exactly match an available one, it is assumed it corresponds to an interval. For example
19.3 gets substituted by
19.3+, which will match all 19.3.x versions, and the latest one will be selected:
$ cs java-home --jvm graalvm:19.3 # picks graalvm:19.3.1 ~/.firstname.lastname@example.org
$ cs java --jvm openjdk:14 -version # picks openjdk:1.14.0 openjdk version "14" 2020-03-17 OpenJDK Runtime Environment (build 14+35-1460) OpenJDK 64-Bit Server VM (build 14+35-1460, mixed mode, sharing)
If one only specifies a version, with no JVM type upfront, AdoptOpenJDK is used by default. This feature can be combined with version intervals above:
$ cs java --jvm 11 -version # picks adopt:11.0.6 openjdk version "11.0.6" 2020-01-14 OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.6+10) OpenJDK 64-Bit Server VM AdoptOpenJDK (build 11.0.6+10, mixed mode)
$ cs java --jvm 13 -version # picks adopt:13.0.2 openjdk version "13.0.2" 2020-01-14 OpenJDK Runtime Environment AdoptOpenJDK (build 13.0.2+8) OpenJDK 64-Bit Server VM AdoptOpenJDK (build 13.0.2+8, mixed mode, sharing)
--env to the
java command makes it print a bash script that sets the right environment variables for a JVM to be used:
$ cs java --jvm 11 --env export JAVA_HOME="/email@example.com" export PATH="/firstname.lastname@example.org/bin:$PATH"
This script can be evaluated for the specified JVM to be used:
$ eval "$(cs java --jvm 11 --env)" $ java -version openjdk version "11.0.6" 2020-01-14 OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.6+10) OpenJDK 64-Bit Server VM AdoptOpenJDK (build 11.0.6+10, mixed mode)
Note that on macOS,
PATH isn't updated, as the default
java binary reads
JAVA_HOME and start
Revert the changes made to the environment variables with
$ eval "$(cs java --disable)"
Note that you can call
--env several times. Calling
--disable once will revert to the state right before the first call to
$ eval "$(cs java --jvm 11 --env)" $ eval "$(cs java --jvm 13 --env)" $ eval "$(cs java --disable)" # reverts both commands above
Setting a default JVM version
The previous section explains how to generate environment settings for a specific JVM version using the
--env option in
This is useful when a particular, one-off version of Java is needed, but it doesn't set a default Java version. In order to do the latter, the
--setup option does the trick.
For example, suppose we want to set the default JVM to AdoptOpenJDK 11. We can achieve this by running the following command:
$ cs java --jvm adopt:11 --setup
Note that this command will update shell configuration files. In order to see the effect of these updates, it is recommended to stop terminal sessions that were already running and start new sessions.
Managed JVM directory
The default directory for JVMs managed by coursier is OS-specific:
%LOCALAPPDATA%\Coursier\Cache\jvm, typically looking like
It can be changed via
COURSIER_JVM_CACHEenvironment variable, or
Note that the
setup commands also accept a custom managed JVM directory via
$ cs java --jvm-dir my-custom-directory --jvm 11 -version Extracting /Users/alex/Library/Caches/Coursier/v1/https/github.com/AdoptOpenJDK/openjdk11-binaries/releases/download/jdk-11.0.6%252B10/OpenJDK11U-jdk_x64_mac_hotspot_11.0.6_10.tar.gz in email@example.com Done openjdk version "11.0.6" 2020-01-14 OpenJDK Runtime Environment AdoptOpenJDK (build 11.0.6+10) OpenJDK 64-Bit Server VM AdoptOpenJDK (build 11.0.6+10, mixed mode)
Parsing of arguments by the
java command parses its arguments differently than the other coursier commands.
It parses its arguments until it gets an option it doesn't recognize (see
cs java --help for the list of options it accepts). All arguments from the first it doesn't recognize are passed as is to the
java process it starts. For example, in
cs java --jvm 11 -Xmx32m -version, it doesn't recognize
-Xmx32m. So both
-version are passed to
java as is.
System JVM detection
java-home commands use the JVM setup on your system by default.
In order to find it, they successively:
- check the
- on macOS, run
- on Linux and Windows, check for a
If none of these methods finds a JVM, it is assumed no JVM was installed prior to running
cs java or
cs java-home. Running one of these command will install the default JVM (as of writing this, the latest AdoptOpenJDK 8 in the JVM index).