79 lines
3.8 KiB
Markdown
79 lines
3.8 KiB
Markdown
# Introduction to JVM Packaging Concepts
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For those of you new to the JVM who have never touched Maven in anger:
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don't panic. Leiningen is designed with you in mind. Leiningen is
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built on some Maven libraries; specifically the dependency resolution
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parts. These aspects of Maven are not nearly as complex as the build
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features that have given it its somewhat fearsome reputation. Think of
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it as the package manager of the JVM world, much like Rubygems, CPAN,
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etc. There is a central canonical Java-centric repository, a
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Clojure-specific repository called Clojars, and projects often also
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make their jars available through project-specific public
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repositories. It allows you to define the dependencies of your
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project, which it then goes and retrieves, stores in a local
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repository ("~/.m2" on Unix by default), and copies into your
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project's "lib/" directory. This makes it so that you don't have to
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check your dependent jar files into your SCM or make developers hunt
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down dependency jars by hand.
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Leiningen describes packages using identifiers that look like:
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org.clojure/swank-clojure "1.0"
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* "org.clojure" is called the 'group-id'
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* "swank-clojure" is called the 'artifact-id'
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* "1.0" is the version of the jar file you require
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Sometimes versions will end in "-SNAPSHOT". This means that it is not
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an official release but a development build. In general relying on
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snapshot dependencies is discouraged, but sometimes its necessary if
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you need bug fixes etc. that have not made their way into a release
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yet. Adding a snapshot dependency to your project will cause Leiningen
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to actively go seek out the latest version of the dependency every
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time you run "lein deps", (whereas normal release versions just use
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the local cache) so if you have a lot of snapshots it will slow things
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down.
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While it's customary to make group IDs match either artifact IDs or
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the Java package, it's not required. Let's take for an example the
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[JYaml jar](http://jyaml.sourceforge.net). Looking at their javadocs,
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the Java package name is "org.ho.yaml". If you try to add the
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following dependency in your project.clj file:
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[org.ho.yaml/jyaml "1.3"]
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You'll get an error when you run "lein deps" because the group id
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doesn't match the package name in this case. One way to find the
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correct group id is to use a maven search web site like
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[Jarvana](http://jarvana.com). In the "project search" box, enter
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"jyaml", and you'll see results that indicate the correct group-id
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("org.jyaml") and artifact id ("jyaml").
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If the jar you're looking for is published in a project's own public
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repository instead of the central one, you can use the :repositories
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option in project.clj. For instance, if we wanted to use the jars from
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the HornetQ project:
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(defproject com.motionbox.hornetq/dashboard "0.0.1-SNAPSHOT"
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:description "a simple web interface to the hornetq jmx API"
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;; this repository will be referred to in log messages as "jboss-release"
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:repositories {"jboss-release" "http://repository.jboss.org/maven2"}
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:dependencies [[org.clojure/clojure "1.1.0"]
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[org.clojure/clojure-contrib "1.0-SNAPSHOT"]
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[commons-logging "1.1.1"]
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[org.hornetq/hornetq-core "2.0.0.GA"]
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[org.hornetq/hornetq-jms-client "2.0.0.GA"]
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[org.hornetq/hornetq-transports "2.0.0.GA"]
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[org.hornetq/hornetq-logging "2.0.0.GA"]
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[org.jboss.netty/netty "3.1.0.GA"]
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[org.jboss.javaee/jboss-jms-api "1.1.0.GA"]
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[log4j "1.2.15" :exclusions [javax.mail/mail
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javax.jms/jms
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com.sun.jdmk/jmxtools
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com.sun.jmx/jmxri]]
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]
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:dev-dependencies [[swank-clojure "1.1.0"]]
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:namespaces [com.motionbox.hornetq])
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For an in-depth walkthrough see the Full Disclojure screencast:
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http://vimeo.com/8934942
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