Maven for eXo VN

Apache Maven @ eXo Platform
Hanoï – 09 Feb 2010

Arnaud Héritier
eXo Platform
Software Factory Manager

Apache Maven
OVERVIEW

Licensed under a Creative Commons license

Apache Maven
BASICS

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Definition
●  Apache Maven is a software project management
and comprehension tool.
●  Based on the concept of a project object model
(POM), Maven can manage a project's build,
binaries, reporting and documentation from a
central piece of information.
●  Apache Maven is a command line tool with some
IDE integrations.


Conventions
●  1 project = 1 artifact (pom, jar, war, ear, …)

●  Standardized
-  directories layout
-  project descriptor (POM)
-  build lifecycle

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POM
●  An XML file (pom.xml) <?xml version="1.0" encoding="UTF-8"?>!
<project>!
<modelVersion>4.0.0</modelVersion>!
<groupId>org.apache.maven</groupId>!

●  Describing <artifactId>webapp-sample</artifactId>!
<version>1.1-SNAPSHOT</version>!
-  Project identification <packaging>war</packaging>!
<name>Simple webapp</name>!
-  Project version <inceptionYear>2007</inceptionYear>!
-  Project description <dependencies>!
<dependency>!
-  Build settings <groupId>org.springframework</groupId>!

-  Dependencies <artifactId>spring-struts</artifactId>!
<version>2.0.2</version>!
-  … </dependency>!
...!
</dependencies>!
</project>!


Dependencies
Without Maven With Maven


Dependencies
●  Declaratives
-  groupId + artifactId + version (+ classifier)
-  Type (packaging) : jar, war, pom, ear, …

●  Transitives
-  Lib A needs Lib B
-  Lib B needs Lib C
-  Thus Lib A needs Lib C


Dependencies
●  Scope
-  Compile (by default) : Required to build and run the
application
-  Runtime : not required to build the application but
needed at runtime
●  Ex : taglibs
-  Provided : required to build the application but not
needed at runtime (provided by the container)
●  Ex : Servlet API, Driver SGBD, …
-  Test : required to build and launch tests but not needed
by the application itself to build and run
●  Ex : Junit, TestNG, DbUnit, …
-  System : local library with absolute path
●  Ex : software products

Dependencies
●  Define all dependencies you are using
-  and no more !
●  Cleanup your dependencies with
-  mvn dependency:analyze!
●  Study your dependencies with
-  mvn dependency:tree!
-  mvn dependency:list!


Artifact Repository
●  By default :
-  A central repository
●  http://repo1.maven.org/
maven2
●  Several dozen of Gb of OSS
libraries
-  A local repository
●  ${user.home}/.m2/repository
●  All artifacts
-  Used by maven and its
plugins
-  Used by your projects
(dependencies)
-  Produced by your projects


Artifact Repository
●  By default Maven
downloads artifacts
required by the project or
itself from central
●  Downloaded artifacts are
stored in the local
repository


Versions
●  Project and dependency versions
●  Two different version variants
  SNAPSHOT version
●  The version number ends with –SNAPSHOT
●  The project is in development
●  Deliveries are changing over the time and are overridden
after each build
●  Artifacts are deployed with a timestamp on remote
repositories
  RELEASE version
●  The version number doesn’t end with –SNAPSHOT
●  Binaries won’t change

Versions


Versions
●  About SNAPSHOT dependencies
-  Maven allows the configuration of an update policy.
The update policy defines the recurrence of checks if
there is a new SNAPSHOT version available on the
remote repository :
●  always
●  daily (by default)
●  interval:X (a given period in minutes)
●  never
-  Must not be used in a released project
●  They can change thus the release also 
●  The release plugin will enforce it 


Versions
●  Use the versions plugin to update all versions in all
POMs
-  mvn versions:set  
–DnewVersion=A.B.C-SNAPSHOT!


Profiles
●  Allow to modify the default behavior of Maven by
overriding/adding some settings
●  Use mvn help:active-profiles to debug
●  Explicit activation or deactivation
mvn <phases or goals> !
-PprofileId1,-profileId2 !
-P!profileId3!


Profiles
●  activeByDefault = If no other profile is activated
●  Activation through Maven settings
<settings>!
...!
<activeProfiles>!
<activeProfile>profile-1</activeProfile>!
</activeProfiles>!
...!
</settings>!


Profiles
●  Activation based on environment variables
<profiles>! <profiles>!

<profile>! <profile>!

<activation>! <activation>!

<property>! <property>!
<name>!skip-enforce</name>!
<name>run-its</name>!
</property>!
<value>true</value>!
</activation>!
</property>!
...!
</activation>!
</profile>!
...!
</profiles>!
</profile>!
</profiles>!


Profiles
●  OS / Java settings
<profiles>! <profiles>!
<profile>!
<profile>!
<activation>!
<activation>!
<os>!
<jdk>[1.3,1.6)</jdk>!
<name>Windows XP</name>!
</activation>!
<family>Windows</family>!
...!
<arch>x86</arch>!
</profile>!
<version>5.1.2600</version>!
</profiles>!
</os>!
</activation>!
...!
</profile>!
</profiles>!

Profiles
●  Activation on present or missing files
<profiles>!
<profile>!
<activation>!
<file>!
<missing>${project.build.directory}/generated-sources/
axistools/wsdl2java/org/apache/maven</missing>!
</file>!
</activation>!
...!
</profile>!
</profiles>!


Reactor
●  Ability of Maven to build pom.xml :
several sub-modules <modules>
resolving the order of their <module>moduleA</module>
dependencies <module>moduleC</module>

●  Modules have to be <module>moduleB</module>
defined in the POM </modules>

-  For a performance reasons


Inheritence
●  Share settings between
projects/modules
●  Project
-  Business1
●  Jar
●  War
-  Business2
●  Jar pom.xml for module Jar1
●  War <parent>

●  By default the parent <groupId>X.Y.Z</groupId>
project is supposed to be <artifactId>jars</artifactId>
in the parent directory <version>1.0-SNAPSHOT<version>
(../) </parent>


Build Lifecycle And Plugins
●  Plugin based architecture
for a great extensibility
●  Standardized lifecycle to
build all types of
archetypes


Apache Maven
GOOD & BAD PRACTICES


Apache Maven
KISS


K.I.S.S.
●  Keep It Simple, Stupid
●  Start from scratch
-  Do not copy/paste what you find without understanding
●  Use only what you need
-  It’s not because maven offers many features that you
need to use them
●  Filtering
●  Modules
●  Profiles
●  …


Apache Maven
PROJECT ORGANIZATION


Project bad practices
●  Ignore Maven conventions
-  Except if your are migrating from something else and
the target has to be to follow them.
-  Except if they are not compatible with your IDE
●  Different versions in sub-modules
-  In that case they are standalone projects.
●  Too many inheritance levels
-  It makes the POMs maintenance more complex
-  Where should I set this plugin parameter ? In which parent ?


Project bad practices
●  Have too many modules
-  Is there a good reason ?
●  Technical constraint ?
●  Team organization ?
-  It increases the build time
●  Many more artifacts to generate
●  Dependencies resolution more complex
-  It involves more complex developments
●  More modules to import in your IDE
●  More modules to update …


Project good practices
●  Use the default
inheritance :
-  The reactor project is also
the parent of its modules.
-  Configuration is easier :
●  No need to redefine SCM
settings, site distribution
settings …


Apache Maven
POM GOOD & BAD PRACTICES


POM bad practices
●  Dependencies :
-  DON’T confuse dependencies and
dependencyManagement
●  Plugins :
-  DON’T confuse plugins and pluginManagement
-  DON’T use AntRun plugin everywhere
-  DON’T let Maven choose plugins versions for you


POM bad practices
●  Profiles :
-  DON’T create environment dependant builds
-  DON’T rely on dependencies coming from profiles
(there is no transitive activation of profiles)
●  Reporting and quality
-  DON’T activate on an existing project all reports with
default configuration
-  DON’T control formatting rules without giving settings
for IDEs.
●  DON’T put everything you find in your POM.


POM good practices
●  Set versions of dependencies in project parent’s
dependencyManagement
●  Set dependencies (groupId, artifactId, scope) in
each module they are used
●  Use the dependency plugin (from apache) and
versions plugin (from mojo) to analyze, cleanup
and update your dependencies.


Apache Maven
DEVELOPMENT


Development bad practices
●  DON’T spend your time in the terminal,
●  DON’T exchange libraries through emails,
●  DON’T always use "-Dmaven.test.skip=true”
●  DON’T manually do releases


Development good practices
●  Keep up-to-date your version of Maven
-  For example in 2.1 the time of dependencies/modules
resolution decreased a lot (Initialization of a project of
150 modules passed from 8 minutes to less than 1)
●  Use the reactor plugin (Maven < 2.1) or native
reactor command line options (Maven >= 2.1) to
rebuild only a subpart of your project :
-  All modules depending on module XXX
-  All modules used to build XXX
●  Try to not use Maven features not supported by
your IDE (resources filtering with the plugin
eclipse:eclipse)

Apache Maven
TO GO FURTHER …


Apache Maven
DOCUMENTATIONS


Some links
●  The main web site :
-  http://maven.apache.org
●  Project’s team wiki :
-  http://docs.codehaus.org/display/MAVEN
●  Project’s users wiki :
-  http://docs.codehaus.org/display/MAVENUSER


Books
●  Sonatype / O’Reilly :
-  The Definitive Guide
-  http://www.sonatype.com/
books
-  Free download
-  Available in several
languages
●  Soon in French


Books
●  Exist Global
-  Better builds with Maven
-  http://www.maestrodev.com/
better-build-maven
-  Free download


Books
●  Nicolas De loof
Arnaud Héritier
-  Published by Pearson
-  Collection Référence
-  Based on our own
experiences with Maven.
From beginners to experts.
-  In French only
-  Available on 20th November


Apache Maven
QUESTIONS ?


Licence et copyrights
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authors/owners
●  Content under Creative Commons 3.0
-  Attribution — You must attribute the work in the manner specified by the
author or licensor (but not in any way that suggests that they endorse you or
your use of the work).
-  Noncommercial — You may not use this work for commercial
purposes.
-  Share Alike — If you alter, transform, or build upon this work, you may
distribute the resulting work only under the same or similar license to this one.
●  http://creativecommons.org/licenses/by-nc-sa/3.0/us/


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