8 Jan 2011 rkrishnan   » (Journeyer)

Embracing maven

After several failed attempt to understand maven and going back and forth between lein and maven, I have finally decided to settle on maven. There are several reasons for this. One of the most important one is that Debian has a very well packaged maven and a local repository system. i.e. Debian java packages installed on a machine is available as a local repo. With that, offline builds become quite easy (provided all the dependencies are available as Debian packages). Maven is also well supported by the Java ecosystem. Though XML turns me off as well, maven takes care of generating much of the boilerplate for us.

I will walk through creating a trivial clojure project using maven. I assume that maven is already installed on your machine.

First, run the following command:

$ mvn archetype:create -DgroupId=in.clj.hello -DartifactId=hello

This gives the following output on my machine: [INFO] Scanning for projects... [INFO] Searching repository for plugin with prefix: 'archetype'. [INFO] ------------------------------------------------------------------------ [INFO] Building Maven Default Project [INFO] task-segment: [archetype:create] (aggregator-style) [INFO] ------------------------------------------------------------------------ [INFO] Setting property: classpath.resource.loader.class => 'org.codehaus.plexus.velocity.ContextClassLoaderResourceLoader'. [INFO] Setting property: velocimacro.messages.on => 'false'. [INFO] Setting property: resource.loader => 'classpath'. [INFO] Setting property: resource.manager.logwhenfound => 'false'. [INFO] [archetype:create {execution: default-cli}] [WARNING] This goal is deprecated. Please use mvn archetype:generate instead [INFO] Defaulting package to group ID: in.clj.hello [INFO] ---------------------------------------------------------------------------- [INFO] Using following parameters for creating OldArchetype: maven-archetype-quickstart:RELEASE [INFO] ---------------------------------------------------------------------------- [INFO] Parameter: groupId, Value: in.clj.hello [INFO] Parameter: packageName, Value: in.clj.hello [INFO] Parameter: package, Value: in.clj.hello [INFO] Parameter: artifactId, Value: hello [INFO] Parameter: basedir, Value: /tmp/hello-mvn [INFO] Parameter: version, Value: 1.0-SNAPSHOT [INFO] ********************* End of debug info from resources from generated POM *********************** [INFO] OldArchetype created in dir: /tmp/hello-mvn/hello [INFO] ------------------------------------------------------------------------ [INFO] BUILD SUCCESSFUL [INFO] ------------------------------------------------------------------------ [INFO] Total time: 1 second [INFO] Finished at: Wed Apr 21 22:13:22 IST 2010 [INFO] Final Memory: 15M/150M [INFO] ------------------------------------------------------------------------

A directory called hello is created. Let us look at the parameters to archetype:create. groupId is a unique way to identify the module. Think of it as the namespace. artifactId is the name of the project. groupId:artifactId:version uniquely identify an ‘artifact’. By default, maven will create a version number 1.0-SNAPSHOT for the project, if it is omitted from commandline.

The directory tree at this point looks like this:

$ tree
.
|-- pom.xml
`-- src
    |-- main
    |   `-- java
    |       `-- in
    |           `-- clj
    |               `-- hello
    |                   `-- App.java
    `-- test
        `-- java
            `-- in
                `-- clj
                    `-- hello
                        `-- AppTest.java
Let us get rid of the java files first. $ rm -rf src/main/java $ rm -rf src/test Create the following directory structure: $ mkdir -p src/main/clojure/in/clj Note that we have created the structure according to our groupId specification. Create a file called hello.clj at the leaf of this directory and put the following contents inside it:
REXML could not parse this XML/HTML: 
<pre>
(ns in.clj.hello)

(defn greet & args (apply str args)) </pre>

Now, open the pom.xml file. Some changes needs to be done here so that maven knows that we are building a clojure project and the dependencies. The following things are done:

  1. The dependency on junit is removed.
  2. A dependency on clojure is added.
  3. A new plugin clojure-maven-plugin is added and configured.
  4. Repositories from where, dependencies are fetched, are added.
At the end of this process, the pom.xml looks like this:
REXML could not parse this XML/HTML: 
<pre>
<span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">project</span> <span class="nxml-namespace-attribute-xmlns">xmlns</span>=<span class="nxml-namespace-attribute-value-delimiter">"</span><span class="nxml-namespace-attribute-value">http://maven.apache.org/POM/4.0.0</span><span class="nxml-namespace-attribute-value-delimiter">"</span> <span class="nxml-namespace-attribute-xmlns">xmlns</span><span class="nxml-namespace-attribute-colon">:</span><span class="nxml-namespace-attribute-prefix">xsi</span>=<span class="nxml-namespace-attribute-value-delimiter">"</span><span class="nxml-namespace-attribute-value">http://www.w3.org/2001/XMLSchema-instance</span><span class="nxml-namespace-attribute-value-delimiter">"</span>
  <span class="nxml-attribute-prefix">xsi</span><span class="nxml-attribute-colon">:</span><span class="nxml-attribute-local-name">schemaLocation</span>=<span class="nxml-attribute-value-delimiter">"</span><span class="nxml-attribute-value">http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd</span><span class="nxml-attribute-value-delimiter">"</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">modelVersion</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">4.0.0</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">modelVersion</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">groupId</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">in.clj.hello</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">groupId</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">artifactId</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">hello</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">artifactId</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">packaging</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">jar</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">packaging</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">version</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">1.0-SNAPSHOT</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">version</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">name</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">hello</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">name</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">url</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">http://maven.apache.org</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">url</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">description</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">project to demonstrate maven</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">description</span><span class="nxml-tag-delimiter">&gt;</span>
<
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">plugins</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">plugin</span><span class="nxml-tag-delimiter">&gt;</span>
    <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">groupId</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">com.theoryinpractise</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">groupId</span><span class="nxml-tag-delimiter">&gt;</span>
    <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">artifactId</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">clojure-maven-plugin</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">artifactId</span><span class="nxml-tag-delimiter">&gt;</span>
    <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">version</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">1.3.2</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">version</span><span class="nxml-tag-delimiter">&gt;</span>
    <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">executions</span><span class="nxml-tag-delimiter">&gt;</span>
      <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">execution</span><span class="nxml-tag-delimiter">&gt;</span>
        <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">id</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">compile-clojure</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">id</span><span class="nxml-tag-delimiter">&gt;</span>
        <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">phase</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">compile</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">phase</span><span class="nxml-tag-delimiter">&gt;</span>
        <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">goals</span><span class="nxml-tag-delimiter">&gt;</span>
          <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">goal</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">compile</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">goal</span><span class="nxml-tag-delimiter">&gt;</span>
        <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">goals</span><span class="nxml-tag-delimiter">&gt;</span>
      <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">execution</span><span class="nxml-tag-delimiter">&gt;</span>
    <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">executions</span><span class="nxml-tag-delimiter">&gt;</span>
    <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">configuration</span><span class="nxml-tag-delimiter">&gt;</span>
      <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">sourceDirectories</span><span class="nxml-tag-delimiter">&gt;</span>
        <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">sourceDirectory</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">src/main/clojure</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">sourceDirectory</span><span class="nxml-tag-delimiter">&gt;</span>
      <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">sourceDirectories</span><span class="nxml-tag-delimiter">&gt;</span>
    <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">configuration</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">plugin</span><span class="nxml-tag-delimiter">&gt;</span>
<span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">plugins</span><span class="nxml-tag-delimiter">&gt;</span>
<<
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">dependency</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">groupId</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">org.clojure</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">groupId</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">artifactId</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">clojure</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">artifactId</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">version</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">1.1.0</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">version</span><span class="nxml-tag-delimiter">&gt;</span>
<span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">dependency</span><span class="nxml-tag-delimiter">&gt;</span>
<<
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">repository</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">id</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">clojure-snapshots</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">id</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">url</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">http://build.clojure.org/snapshots</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">url</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">releases</span><span class="nxml-tag-delimiter">&gt;</span>
    <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">enabled</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">false</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">enabled</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">releases</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">snapshots</span><span class="nxml-tag-delimiter">&gt;</span>
    <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">enabled</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">true</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">enabled</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">snapshots</span><span class="nxml-tag-delimiter">&gt;</span>
<span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">repository</span><span class="nxml-tag-delimiter">&gt;</span>
<span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">repository</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">id</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">clojure-releases</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">id</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">url</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">http://build.clojure.org/releases</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">url</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">releases</span><span class="nxml-tag-delimiter">&gt;</span>
    <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">enabled</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">true</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">enabled</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">releases</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">snapshots</span><span class="nxml-tag-delimiter">&gt;</span>
    <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-element-local-name">enabled</span><span class="nxml-tag-delimiter">&gt;</span><span class="nxml-text">false</span><span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">enabled</span><span class="nxml-tag-delimiter">&gt;</span>
  <span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">snapshots</span><span class="nxml-tag-delimiter">&gt;</span>
<span class="nxml-tag-delimiter">&lt;</span><span class="nxml-tag-slash">/</span><span class="nxml-element-local-name">repository</span><span class="nxml-tag-delimiter">&gt;</span>
<<
REXML could not parse this XML/HTML: 
</pre>
REXML could not parse this XML/HTML: 
</pre>

Now do: $ mvn package This produces the following output on my machine:

[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------------
[INFO] Building hello
[INFO]    task-segment: [package]
[INFO] ------------------------------------------------------------------------
[INFO] [resources:resources {execution: default-resources}]
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /tmp/hello-mvn/hello/src/main/resources
[INFO] [compiler:compile {execution: default-compile}]
[INFO] No sources to compile
[INFO] [clojure:compile {execution: compile-clojure}]
Compiling in.clj.hello to /tmp/hello-mvn/hello/target/classes
[INFO] [resources:testResources {execution: default-testResources}]
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /tmp/hello-mvn/hello/src/test/resources
[INFO] [compiler:testCompile {execution: default-testCompile}]
[INFO] No sources to compile
[INFO] [surefire:test {execution: default-test}]
[INFO] No tests to run.
[INFO] [jar:jar {execution: default-jar}]
[INFO] Building jar: /tmp/hello-mvn/hello/target/hello-1.0-SNAPSHOT.jar
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 4 seconds
[INFO] Finished at: Wed Apr 21 22:57:11 IST 2010
[INFO] Final Memory: 23M/121M
[INFO] ------------------------------------------------------------------------
A jar file is created under the target directory. Now, we add the jar into our classpath and invoke the clojure repl: $ java -cp /usr/share/java/clojure.jar:target/hello-1.0-SNAPSHOT.jar clojure.main Clojure 1.1.0 user=> (use 'in.clj.hello) nil user=> (greet "Hello World") "Hello World" user=> You can also invoke the repl from maven: $ mvn clojure:repl That wasn’t really too hard. With emerging tools around maven like the Polyglot Maven which supports Clojure and a S-expression syntax for writing the POM, we don’t even have to do as much as we did now. I have put this example in this repository for anyone to play with.

Syndicated 2010-04-21 07:00:00 from Ramakrishnan Muthukrishnan

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