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.
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.
The files jem needs to operate are stored in the following locations
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 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 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
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 is generated from jem sources in the docs subdirectory after compiling jem. API documentation is created using doxygen and man page created from help2man.
# 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
jem binaries and sources are currently available for download via releases.
jem can be compiled via autotools or ninja, based on which generator is used for cmake
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
After configuring via cmake, to compile jem run make or ninja as normal in the root directory of the sources.
make
To see all make targets
make help
To build tests
make jem-test
ninja
To see all make targets
ninja help
To build tests
ninja jem-test
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.
Install using autotools
make install
Install using ninja
ninja install
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.
make package
ninja package