jar-dependencies
add gem dependencies for jar files to ruby gems.
getting control back over your jar
jar dependencies are declared in the gemspec of the gem using the same notation as https://github.com/mkristian/jbundler.
when using require_jar to load the jar into JRuby's classloader then an version conflict will be detected and only ONE jar gets loaded. jbundler allows to select the version suitable for you application.
most maven-artifact do NOT use versions ranges but depends pick a version. then jbundler can always overwrite any such version.
vendoring your jars before packing the jar
add to your Rakefile following:
require 'jar_installer'
task :install_jars do
Jars::JarInstaller.vendor_jars
end
which will install download the dependent jars into JARS_HOME and creats a file lib/my_gem_jars.rb which is just an enumeration of require_jars statements to load all the jars. the vendor_jars will copy them into the lib directory of the gem.
the location where jars are cached is per default $HOME/.m2/repository the same default as maven has to cache the jar-artifacts. it respects $HOME/.m2/settings.xml from maven with all its mirror and other settings or the environment variable JARS_HOME.
IMPORTANT: make sure that jar-dependencies is only a development dependency of your gem. if it is a runtime dependencies the require_jars file will be overwritten during installation.
reduce the download and reuse the jars from maven local repository
if you do not vendor the jars into gem then the jar-dependency gem can vendor them when you install the gem. just skip use Jars::JarInstaller.install_jars from the above rake tasks.
until JRuby itself comes with this jar-dependencies as default gem, for this feature to work you need to install the jar-dependencies gem first and for bundler you need to use the bundle-with-jars command :(
IMPORTANT: make sure that jar-dependencies is a runtime dependency of your gem so the require_jars file will be overwritten during installation with the "correct" versions of the jars.
for development you do not need to vendor the jars at all
just set an environment variable
export JARS_VENDOR=false
this tells the jar_installer not vendor any jars but only create the file with the require_jar statements. this require_jars method will find the jar inside the maven local repository and loads it from there.
some drawbacks
* first you need to install the jar-dependency gem with its development dependencies installed (then ruby-maven gets installed as well)
* bundler does not install the jar-dependencies (unless JRuby adds the gem as default gem)
* you need ruby-maven doing the job of dependency resolution and downloading them. gems not part of <http://rubygems.org> will not work currently
jar others then from maven-central
per default all jars need to come from maven-central (<search.maven.org>), in order to use jars from any other repo you need to add it into your settings.xml and configure it in a way that you use it without interactive prompt (username + passwords needs to be part of settings.xml).
NOTE: gems depending on jars other then maven-central will NOT work when they get published on rubygems.org since the user of those gems will not have the right settings.xml to allow them to access the jar dependencies.
examples
an example with rspec and all walks you through setup and shows how development works and shows what happens during installation.
there are some more examples with the various project setups for gems and application. this includes using proper maven for the project or ruby-maven with rake or the rake-compiler in conjuction with jar-dependencies.
configuration
| ENV | java system property | default | description |
| `JARS_DEBUG` | jars.debug | false | if set to true it will produce lots of debug out (maven -X switch) |
| `JARS_VERBOSE` | jars.verbose | false | if set to true it will produce some extra output |
| `JARS_HOME` | jars.home | $HOME/.m2/repository | filesystem location where to store the jar files and some metadata |
| `JARS_MAVEN_SETTINGS` | jars.maven.settings | $HOME/.m2/settings.xml | setting.xml for maven to use |
| `JARS_VENDOR` | jars.vendor | true | set to true means that the jars will be stored in JARS_HOME only |
| `JARS_SKIP` | jars.skip | true | do **NOT** install jar dependencies at all |
motivation
just today I tumbled across https://github.com/arrigonialberto86/ruby-band which usees jbundler to manage their jar dependencies which happens on the first 'require "ruby-band"'. their is no easy or formal way to find out which jars are added to jruby-classloader.
another issue was brought to my notice yesterday mmmries/derelicte#1
or the question of how to manage jruby projects with maven http://ruby.11.x6.nabble.com/Maven-dependency-management-td4996934.html
or a few days ago an issue for the rake-compile rake-compiler/rake-compiler#87
with jruby-9000 coming it is the right time to get the jar dependencies right - the current situation is like the time before bundler for gems.