An Introduction to Maven

An Introduction to Apache

Author: Vadim Lotar (QC Backend)
2011

Agenda
 Automation Build Tool
 A bit of history
 Why Maven?
 An Introduction to Maven
 Drawbacks of Maven
 Best practices
 Maven in software development suite
 Examples
 Q&A

Automation Build Tool
 Since the early days of modern
engineering, automation of build
processes has been the key to:

 Productivity improvements
 Quality insurance
 Eliminate dependencies on key
personnel
 Save time and money

 Why would software development
be any different?

Automation Build Tool
 How do you really enable automation of
build?

 Build has to be reproducible

 Build has to produce the final production artifact

 Build has to be as easy to maintain as possible
and well documented

A bit of history
 A simple script (.sh, .bat) is already a possible
solution

 More advanced command-line tools have been
available for a long time

 make created in 1977 at Bells Labs by Stuart
Feldman. Still very much used nowadays

 Apache Ant created by James Duncan Davidson

A bit of history
Two main categories in current tools:
 Scripting tools
 Ant
 Rake (Ruby based)
 Gradle (Groovy based)
 … many others

 Artifact oriented tools
 Maven
 Debian Package Creation

A bit of history
 Maven 1.x is now almost 12 years old
project, mostly motionless since 2007 (I cannot
find anybody still using it or committing to it)
 Maven 2.x was the de facto standard for Java and
Java EE build
 Most open source projects were switched to
Maven for their build system
 It’s now seven years old
 Maven 3.x is used in > 90% of Java (EE) startup
applications.
 It’s now two years old
 Last release – ver. 3.0.3

Why Maven?
 If you are not already using it:
 Now is the best moment to start being aware
 Maven is mature
 Maven is getting better and better
 Maven can be used online and offline
 If you are already using it:
 Hang on! The best is yet to come!
 Focus on necessary things and don’t get
frustrated by petty details

An Introduction to Maven
Maven is a tool with multiple facets:

 a BUILD tool

 a DEPENDENCY MANAGEMENT tool

 a DOCUMENTATION tool

Project Object Model
pom.xml

Maven’s working …

 Generated artifacts (jar, war, ear…),
 Documentation, statistics (test
results, quality metrics, javadoc, web
site)…

 A project can easily be cut into modules
thanks to Maven
 By simply declaring project metadata and
optionally configuring a few plug-ins, you can:
 Build your project (compile, generate
sources…)
 Launch tests and gather results
(Junit, TestNG, Selenium…etc)
 Package (Jar, War, Ejb, War…etc)
 Document and generate reports

Project Object Model (POM)
 Basic project information
 groupId, artifactId, version…
 Inheritance, or Aggregation through sub-modules
(will explain the difference later on)
 Build section
 Project layout (sources and resources folders… etc)
 Build plugins configuration
 Reporting section
 Reports configuration
 Some other advanced environment settings

 A plug-in is made of a MOJO (Maven POJO)
which is simply a java class with Maven-
specific metadata.
 A plug-in can define goals and reports
 Goals can be called directly:
 mvn plugin:goal
 Goals can be bound to one or multiple phases
 Reports are used during site generation
 mvn site

 When you invoke a phase, Maven will go
through all the phases until the one
specified, executing the bound goals:
 mvn package

 There are many more phases than in
previous examples in the default lifecycle
 By default, all the basic necessary plug-ins
for the build phase are already bound to
phases
 It is easy to have information about plugins:
 mvn help:describe
 So….. what’s left to do, and what’s all the
fuss about the complexity of Maven?

Dependencies: A blessing and a curse
 Blessing:
 Transitive dependencies
 easier to find/discover/use java libraries
 Curse:
 Transitive dependencies can rapidly trigger
a dependency hell!
 Harder to stabilize builds

 What really made Maven different from other
builds systems in the first place?

 REPOSITORIES!!!

 Before Maven, it was really hard to find java
libraries, and harder to ensure a coherent use
of these libraries

 Nowadays, it’s still very hard to find some jars
with a decent/coherent versioning, let alone to
find their sources or javadocs

 Local repository:
 Local cache for artifacts
 Contain temporary build artifacts
 It’s possible to erase it regularly
 Very useful for offline builds
 By default in user home’s .m2/repository folder
 Can be moved to another place through
Maven runtime’ settings.xml file
 $MAVEN_HOME/conf/settings.xml

 Corporate repository/proxy
 Access via file:// and http://
 The first necessary step towards a corporate use of
maven
 The local and remote repositories are structured
the same
 Even better: install a repository management tool
 Can proxy external repositories
 Can filter unwanted artifacts

 Public repositories
 Good for dependencies’ harvesting
 A lot of mis-configured dependencies
 A lot of alpha/beta Maven plugins and
libraries

 Be cautious when adding public repositories to
a build process!
 Should be proxied in corporate

Other key features of Maven:

 POM Inheritance/Aggregation
 Archetypes
 Launching Tests
 … many more…

 POM – Project Object Model

 Super POM

 Inheritance

 Aggregation

 Inheritance vs Aggregation

Project Archetypes

 You can build template projects and make them
available as artifacts in the repositories
 mvn archetype:create-from-project
 Allows to share best practices without neither
inheritance nor aggregation
 mvn archetype:generate
 Many Archetypes already configured in the default
catalog

 You can easily build a custom or corporate catalog
mvn archetype:generate
–DarchetypeCatalog=http://www.corporate.com/archetypes.xml

Archetype ArtifactIds Description
maven-archetype-archetype An archetype which contains a sample
archetype.
maven-archetype-j2ee-simple An archetype which contains a simplifed sample
J2EE application.
maven-archetype-mojo An archetype which contains a sample a sample
Maven plugin.
maven-archetype-plugin An archetype which contains a sample Maven
plugin.
maven-archetype-plugin-site An archetype which contains a sample Maven
plugin site.
maven-archetype-portlet An archetype which contains a sample JSR-268
Portlet.
maven-archetype-quickstart An archetype which contains a sample Maven
project.
maven-archetype-simple An archetype which contains a simple Maven
project.
maven-archetype-site An archetype which contains a sample Maven
site which demonstrates some of the supported
document types like APT, XDoc, and FML and
demonstrates how to i18n your site.
maven-archetype-site-simple An archetype which contains a sample Maven
site.
maven-archetype-webapp An archetype which contains a sample Maven
Webapp project.

Launching Tests

 Maven allows to launch various types of tests:
 Unit tests: Junit 3.x or 4.x, TestNG, …
 UI Tests: Selenium, Canoo Webtest
 Functional tests: Fitnesse, Greenpepper
 WebServices tests: SOAPUi
 And many more…

Drawbacks of Maven
 Library repositories are not always safe.

 Maven Conventions

 Hard to find some things about maven and
plugins

 A huge output log

 Sequential build (Lyfecycle)

 Learning Maven is long in comparison of Ant.

Best practices
 Embrace the standardization brought by Maven, don’t
fight it

 Use POM Inheritance and <dependencyManagement>
(with import scope), <pluginManagement>

 Use a Repository Manager:
 Sonatype Nexus: http://nexus.sonatype.org
 Jfrog Artifactory: http://artifactory.jfrog.org
 …

Best practices
 Keep your build as simple as possible

 Launch your builds regularly and possibly in a neutral
zone

 Use the “dependency” and “versions” plugins

 Generate test statistics data and other metrics data in
order to exploit them in Software quality tools:
 Sonar: http://sonar.codehaus.org
 Squale: http://www.squale.org
 …

Maven in a Software development
suite
 Maven is now very well integrated in IDEs
 NetBeans 6.5+ now has very good support for
Maven
 Eclipse 3.x has very good support also.
 IntelliJ IDEA seems to have excellent support
also (though this is why you pay for it isn’t it?)
 Maven works very well with Quality
monitoring tools
 Continuous integration

References and Thanks
Documentation and information:
 Site http://maven.apache.org
 Plugins
 http://maven.apache.org/plugins
 http://mojo.codehaus.org/
 http://code.google.com/
 And many others…
 Project Wiki
http://docs.codehaus.org/display/MAVEN/
 Users’ Wiki
http://docs.codehaus.org/display/MAVENUSER

References and Thanks
Books
 Free electronic editions:
 Definitive Guide: http://www.sonatype.com/books
 Better Builds with Maven:
http://www.maestrodev.com/better-build-maven
 Upcoming book by Arnaud Héritier and Nicolas De Loof
http://www.pearson.fr/livre/?GCOI=27440100730370

Thanks
 Many thanks to Pierre-Antoine Grégoire for its
presentation on YaJUG
 Thanks to Jason van Zyl for its Maven 3 presentation
http://www.sonatype.com/people/author/jason

An Introduction to Maven

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