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Getting Started with Maven

Written by Bob Aiello

Monday, 02 November 2009 15:10

Maven is a popular build framework that is used by many technology professionals to manage large scale java application development. The Apache Maven website (http://maven.apache.org) states that "Maven is a software project management and comprehension tool". Maven builds are based upon a project object model (POM) which is coded in XML. Maven is used to manage a project's build, reporting and documentation from a central place. I have worked with both Maven 1.0.2 and the very popular Maven 2. For this article I used Maven 2.2.1 on RHEL 5.3.

Setting up the environment
To get started, I downloaded the Maven 2.1.1 as a compressed tar (apache-maven-2.2.1-bin.tar.gz) and unpacked it into a central location (e.g. /usr/local). Then I set the JAVA_HOME to point to the current version of Java (/usr/java/jdk1.6). Then I checked the maven version by typing:

mvn -version

Which displayed
Apache Maven 2.2.1 (r801777; 2009-08-06 15:16:01-0400)

Along with the compiler version and OS name.

Creating your first Maven project
Maven has a very helpful feature where you can create your first project with the following command:

mvn archetype:generate \
-DarchetypeGroupId=org.apache.maven.archetypes \
-DgroupId=com.cmcrossroads.app \
-DartifactId=my-app

You will prompted to enter a number and then to confirm the information entered. You will then see Maven automatically download dependencies from Maven "central".

Note that I abbreviated the output below, but you should see "BUILD SUCCESSFUL" at the end.

[INFO] Scanning for projects...
[INFO] Searching repository for plugin with prefix: 'archetype'.
[INFO] org.apache.maven.plugins: checking for updates from central
[INFO] org.codehaus.mojo: checking for updates from central
[INFO] artifact org.apache.maven.plugins:maven-archetype-plugin: checking for updates from central
Downloading: http://repo1.maven.org/maven2/org/apache/maven/plugins/maven-archetype-plugin/2.0-alpha-4/maven-archetype-plugin-2.0-alpha-4.pom
4K downloaded (maven-archetype-plugin-2.0-alpha-4.pom)
Downloading: http://repo1.maven.org/maven2/org/apache/maven/archetype/maven-archetype/2.0-alpha-4/maven-archetype-2.0-alpha-4.pom
13K downloaded (maven-archetype-2.0-alpha-4.pom)
Downloading: http://repo1.maven.org/maven2/org/apache/maven/maven-parent/9/maven-parent-9.pom
32K downloaded (maven-parent-9.pom)
Downloading: http://repo1.maven.org/maven2/org/apache/apache/4/apache-4.pom
4K downloaded (apache-4.pom)
Downloading: http://repo1.maven.org/maven2/org/apache/maven/plugins/maven-archetype-plugin/2.0-alpha-4/maven-archetype-plugin-2.0-alpha-4.jar
53/63K
63K downloaded (maven-archetype-plugin-2.0-alpha-4.jar)
[INFO] ------------------------------------------------------------------------
[INFO] Building Maven Default Project
[INFO] task-segment: [archetype:generate] (aggregator-style)
[INFO] ------------------------------------------------------------------------
[INFO] Preparing archetype:generate
[INFO] No goals needed for project - skipping
Downloading: http://repo1.maven.org/maven2/org/apache/maven/archetype/archetype-common/2.0-alpha-4/archetype-common-2.0-alpha-4.pom
15K downloaded (archetype-common-2.0-alpha-4.pom)
Downloading: http://repo1.maven.org/maven2/org/apache/maven/maven-core/2.0.8/maven-core-2.0.8.pom
6K downloaded (maven-core-2.0.8.pom)
Downloading: http://repo1.maven.org/maven2/org/apache/maven/maven/2.0.8/maven-2.0.8.pom
11K downloaded (maven-2.0.8.pom)
Downloading: http://repo1.maven.org/maven2/org/apache/maven/maven-parent/6/maven-parent-6.pom

Output abbreviated by Bob Aiello

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 28 seconds
[INFO] Finished at: Sun Oct 04 21:29:15 EDT 2009
[INFO] Final Memory: 10M/151M
[INFO] ------------------------------------------------------------------------

Sample Application Created
This creates a directory structure called my-app which includes a src subdirectory, the maven pom.xml and a readme file:

my-app/src
my-app/pom.xml
my-app/README.txt

The my-app/src directory includes a sample java program (in the main subdirectory) and a test stub (in the test subdirectory).

The pom.xml is the main configuration file for Maven. There is a lot of complexity and power in dissecting and understanding the POM. We'll examine the POM, in detail, in future articles, but this is not the only structure that you need to understand.

Maven also creates a local repository, by default, in your $HOME/.m2 directory. It is important to become familiar with this local repository. By default, you will see a simple App.java program and a test stub called AppTest.java.

> find .
.
./my-app
./my-app/pom.xml
./my-app/src
./my-app/src/main
./my-app/src/main/java
./my-app/src/main/java/com
./my-app/src/main/java/com/cmcrossroads
./my-app/src/main/java/com/cmcrossroads/app
./my-app/src/main/java/com/cmcrossroads/app/App.java
./my-app/src/test
./my-app/src/test/java
./my-app/src/test/java/com
./my-app/src/test/java/com/cmcrossroads
./my-app/src/test/java/com/cmcrossroads/app
./my-app/src/test/java/com/cmcrossroads/app/AppTest.java

Configuring your local Maven repository

The local repository is stored in a directory called ${user.home}/.m2 and stores the configuration items created by the maven build. I have seen some challenges with managing the contents of the .m2 subdirectory. For example, many people do not have much room in their home directory for large builds. You can relocate the .m2 directory by creating a ${user.home}/.m2/settings.xml and specify an alternate location for your local Maven repository:

...

/mylocalrepo/

...

I have also seen files get corrupted during the build and I had to manually deleted them from the .m2 directory. Aside from the unique structure, Maven also has a unique runtime lifecycle.

The Maven lifecycle

It's import to understand the Maven lifecycle

Here is the default lifecycle with description indicated on this link
(http://maven.apache.org/guides/introduction/introduction-to-the-lifecycle.html)

validate - validate the project is correct and all necessary information is available
compile - compile the source code of the project
test - test the compiled source code using a suitable unit testing framework. These tests should not require the code be packaged or deployed
package - take the compiled code and package it in its distributable format, such as a JAR. integration-test - process and deploy the package if necessary into an environment where integration tests can be run
verify - run any checks to verify the package is valid and meets quality criteria
install - install the package into the local repository, for use as a dependency in other projects locally
deploy - done in an integration or release environment, copies the final package to the remote repository for sharing with other developers and projects.

When you run a maven build you indicate the target phase of the lifecycle and all previous steps are run first. We'll go into more detail on how to configure your POM and manage your maven builds in future articles. Please send me your own tips and tricks on Maven builds so that we can include your own best practices!

Bob Aiello is the Editor-in-Chief for CM Crossroads and an independent consultant specializing in Software Process Improvement including Software Configuration and Release Management. Mr. Aiello has over 25 years experience as a technical manager in several top NYC Financial Services firms where he had had company-wide responsibility for CM, often providing hands-on technical support for enterprise Source Code Management tools, SOX/Cobit compliance, build engineering, continuous integration and automated application deployment. Bob is a long standing member of the Steering Committee of the NYC Software Process Improvement Network (CitySPIN), where he serves as the chair of the CM SIG. Mr. Aiello holds a Masters in Industrial Psychology from NYU and a B.S. in Computer Science and Math from Hofstra University. You may contact Mr. Aiello at raiello@acm.org or link with him at http://www.linkedin.com/in/bobaiello .

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