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java

The java and 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)

Likewise, the 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.

Managed JVMs

Both java and 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

JVM index

By default, the java and java-home commands rely on the coursier index. This index is regularly updated, and lists a large variety of JVMs for Linux / macOS / Windows.

This index supports Oracle OpenJDK, AdoptOpenJDK, GraalVM community edition, Zulu, among others.

To list the JVM that can be installed from it, run

$ cs java --available

The JVM index source can be changed by using the --jvm-index option. Possible values are

  • cs (default)

    Uses coursier index

  • cs-maven

    Fetches index from io.get-coursier:jvm-index Maven repository

  • an arbitrary URL

    It's also possible to specify arbitrary URL containing JVM index. For example,

    cs java --available --jvm-index https://url/of/your/index.json

Short JVM names

The full names from the index can be cumbersome to remember and type (adopt:13.0.2, adopt:1.8.0-232, graalvm:19.3.1, etc.).

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
~/.cache/coursier/jvm/graalvm@19.3.1

$ 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)

Environment variables

Passing --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="/home/alex/.cache/coursier/jvm/adopt@1.11.0-6"
export PATH="/home/alex/.cache/coursier/jvm/adopt@1.11.0-6/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 $JAVA_HOME/bin/java itself.

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 --env:

$ 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 cs java.

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:

  • Linux: ~/.cache/coursier/jvm
  • macOS: ~/Library/Caches/Coursier/jvm
  • Windows: %LOCALAPPDATA%\Coursier\Cache\jvm, typically looking like C:\Users\Alex\AppData\Local\Coursier\Cache\jvm

It can be changed via

  • the COURSIER_JVM_CACHE environment variable, or
  • the coursier.jvm.cache Java property.

Note that the java, java-home, and setup commands also accept a custom managed JVM directory via --jvm-dir, like

$ 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
  my-custom-directory/adopt@1.11.0-6
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

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 -Xmx32m and -version are passed to java as is.

System JVM detection

The java and java-home commands use the JVM setup on your system by default.

In order to find it, they successively:

  • check the JAVA_HOME environment variable,
  • on macOS, run /usr/libexec/java_home,
  • on Linux and Windows, check for a java command in PATH.

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).

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