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Universal *nix Java Environment Manager - port of Gentoo's python java-config in C

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jem - Java Environment Manager

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About

jem is a Java Environment Manager, a re-write and port to C of a program on Gentoo Linux called java-config, written in python, specific to Gentoo Linux and derivatives. jem being in C, is Linux distro agnostic and should work for any GNU, eventually POSIX, compliant operating system. The intention is to standardize java management and tools for scripts and programs.

jem provides means to manage and set active, system, and user virtual machines independently. Along with ability to build package classpath and other things for a variety of uses. By using jem systems can have portable and consistent access to java virtual machines and packages.

jem is available as a cli jem and shared object library libjem.so for usage in other languages or applications.

How it works

jem operates using properties style files for packages, vm, and virtuals. These are stored in various locations. Along with some configuration files for finer control. jem sets and manages symlinks for the system and user vm. Along with runtime vm selection via JEM_VM environment variable. Which overrides the system and user vm just for that environment.

jem also provides a wrapper shell script run-java-tool.bash symlinked to all binaries provided in a virtual machine. This allows the script to determine which VM should be used at that time, active, system, or user VM.

Finally of course jem also manages and sets JAVA_HOME environment variable and others needed for standard Java usage via profile.d shell files sourced at start of a shell session.

File locations

The files jem needs to operate are stored in the following locations

Packages package.env

Package files are stored in the following location for each package. All package operations of jem depend on these package.env files.

/usr/share/<package>(?-<slot>)/package.env

# example
/usr/share/jetty-server-9.4/package.env

Virtual Machine

Virtual Machine properties files are stored in the following location. One for each virtual machine on a system. All VM operations of jem depend on these vm properties files.

/etc/jem/vms.d/<vm-package>(?-<slot>)

# example
/etc/jem/vms.d/oracle-jdk-bin-10

Virtual packages

Virtual Packages files, that contain package names for all providers of a given virtual. Used by jem to match an actual package with a virtual.

/etc/jem/virtuals.d/<virtual-package>(?-<slot>)

# example
/etc/jem/virtuals.d/servlet-api-4.0

Virtual packages configuration

Virtuals preference configuration file. Used to bind a virtual package to a specific package of your choosing, or change default order.

/etc/jem/virtuals.conf

Documentation:

Documentation is generated from jem sources in the docs subdirectory after compiling jem. API documentation is created using doxygen and man page created from help2man.

Help Output

# jem --help
Usage: jem [OPTION...]

Java Environment Manager
Copyright 2015-2018 Obsidian-Studios, Inc.
Distributed under the terms of the GNU General Public License v3

 Global Options:
  -n, --nocolor              Disable color output

 VM Options:
  -a, --active-vm=VM, --select-vm=VM
                             Use this vm instead of the active vm when
                             returning information
  -c, --javac                Print the location of the javac executable
  -e, --exec_cmd=COMMAND     Execute something which is in JAVA_HOME
  -f, --show-active-vm       Print the active Virtual Machine
  -g, --get-env=VAR          Print an environment variable from the active VM
  -j, --jar                  Print the location of the jar executable
  -J, --java                 Print the location of the java executable
  -L, --list-vms, --list-available-vms
                             List available Java Virtual Machines
  -o, --jre-home             Print the location of the active JAVA_HOME
  -O, --jdk-home             Print the location of the active JAVA_HOME
  -P, --print=VM             Print the environment for the specified VM
  -r, --runtime              Print the runtime classpath
  -s, --set-user-vm=VM       Set the default Java VM for the user
  -S, --set-system-vm=VM     Set the default Java VM for the system
  -t, --tools                Print the path to tools.jar
  -v, --java-version         Print version information for the active VM

 Package Options:
  -d, --with-dependencies    Include package dependencies in --classpath and
                             --library calls
      --get-virtual-providers=PACKAGE(S)
                             Return a list of packages that provide a virtual
  -i, --library=LIBRARY(s)   Print java library paths for these packages
  -l, --list-packages, --list-available-packages
                             List all available packages on the system
  -p, --classpath=PACKAGE(s) Print entries in the environment classpath for
                             these packages
      --package=PACKAGE(s)   Retrieve a value from a package(s) package.env
                             file, value is specified by --query
  -q, --query=PARAM(s)       Parameter(s) value(s) to retrieve from package(s)
                             package.env file, specified by --package

 GNU Options:

  -?, --help                 Give this help list
      --usage                Give a short usage message
  -V, --version              Print program version

Download:

jem binaries and sources are currently available for download via releases.

Build:

jem can be compiled via autotools or ninja, based on which generator is used for cmake

Configure:

In the root directory of the sources, run the following commands to
configure cmake sources. cmake uses autotools by default. jem can be
built with ninja instead of autotools for faster builds. Little chance
of switching to meson build system.

  • To build jem with debugging symbols
cmake -D CMAKE_BUILD_TYPE=Debug ./
  • To build jem as normal
cmake -D CMAKE_BUILD_TYPE=Release ./
  • To build documentation add -D BUILD_DOC=ON to either
  • To build using ninja instead of autotools add -G Ninja to either

Compiling:

After configuring via cmake, to compile jem run make or ninja as normal in the root directory of the sources.

Autotools

make

To see all make targets

make help

To build tests

make jem-test

Ninja

ninja

To see all make targets

ninja help

To build tests

ninja jem-test

Installing:

Installing jem should be done through the systems package manager. For integration with package managers and/or manual installation you can run the following command.

Autotools

Install using autotools

make install

Ninja

Install using ninja

ninja install

Packaging:

jem's build system can also build DEB, RPM, and TBZ2 packages for distribution. To build all the above targets (they cannot be build individually at this time) run the following command.

Autotools

  make package

Ninja

  ninja package

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Universal *nix Java Environment Manager - port of Gentoo's python java-config in C

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