Introduction to maven

Introduction to
Maven
Manolis Georgopoulos
http://manolis.hemera.mobi
20/09/2013

“Maven” what ?
Official site says that:
“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, reporting and documentation from a
central piece of information.”

…What ???????
Maven is :
o A top-level open source Apache Software Foundation project
o A popular build tool
o A dependency management tool
o A release management tool
The picture describes the Maven
operation and interaction model.

Why Maven?
• Dependency management
• Modularity
• Code reusability
• Abstraction of Build process (no dependency on
IDEs)
• Automated processes (deployments, unit &
integration tests, etc)

Project Structure
src/main/java: Your Java source code goes here
src/main/resources: Other resources your application needs. All
directories or files placed within the src/main/resources directory are
packaged in your JAR with the exact same structure, starting at the
base of the JAR
src/main/filters: Resource filters, in the form of properties files, which
may be used to define variables only known at runtime
src/main/config: Configuration files. The
directory [src/main/config] doesn't show up on the classpath so the
application or test classes can't read anything in it.
src/main/webapp: The Web application directory for a WAR project
src/test/java: Unit tests (will not be deployed)
src/test/resources: Resources to be used for unit tests, but will not be
deployed
src/test/filters: Resources filters to be used for unit tests, but will not
be deployed
src/site: Files used to generate the Maven project Website

Key Concepts
 POM
 Artifacts
 Dependencies
 Lifecycle phases
 Plugins
 Profiles

POM
• POM
o Stands for Project Object Model
o Is Maven’s description of a single project
o Is an XML document
o Contains a detailed description of your project, including information
about versioning and configuration management, dependencies,
application and testing resources, team members and structure, and
much more

POM basic elements
• project – the top level element
• modelVersion - the version of the object model
• groupId – indicates the unique identifier of the organization or group that
created the project
• artifactId – indicates the unique name of the primary artifact being
generated by this project
• packaging – indicates the package type to be used by this artifact (jar,
war, ear, etc). Default value is jar
• version – indicates the version of the artifact generated by the project
• name – indicates the display name used for the project
• url – indicates where the project’s site can be found
• description – provides a basic description for the project
* http://maven.apache.org/ref/3.1.0/maven-model/maven.html

Artifacts
• An artifact is a file (jar, war, ear, etc), that gets deployed to a
Maven repository.
• Maven provides a large database of artifacts in maven
central repository http://search.maven.org/
• Artifact Repository Sonatype Nexus 2.3.x
Proxies maven central repository
Proxies other third party repositories (Apache, jBoss, etc)
Repository for Snapshot artifacts
Repository for Release artifacts
• Repository types
Maven has two types of repositories: local and remote.
Maven usually interacts with your local repository, but when a declared
dependency is not present in your local repository Maven searches all
the remote repositories it has access to in an attempt to find what’s
missing.

Dependencies
• Dependency Management
The key concept is that Maven dependencies are declarative. In the POM you
are not specifically telling Maven where the dependencies are physically, you
are simply telling Maven what a specific project expects.
• Where does that dependency come from ?
When a dependency is declared, Maven tries to satisfy that dependency by
looking in all of the remote repositories that are available, within the context of
your project, for artifacts that match the dependency request. If a matching
artifact is located, Maven transports it from that remote repository to your local
repository for general use.
• Transitive dependencies
Transitive dependencies are a feature introduced in Maven 2.0. This allows you to
avoid needing to discover and specify the libraries that your own dependencies
require, and including them automatically.

Dependencies - Scope
In a real-world enterprise application, you may not need to include all the
dependencies in the deployed application. Some JARs are needed only for unit
testing, while others will be provided at runtime by the application server. Using a
technique called dependency scoping, Maven lets you use certain JARs only
when you really need them and excludes them from the classpath when you
don't.
Maven provides four dependency scopes:
• compile: A compile-scope dependency is available in all phases. This is the default
value.
• provided: A provided dependency is used to compile the application, but will not be
deployed. You would use this scope when you expect the JDK or application server to
provide the JAR. The servlet APIs are a good example.
• runtime: Runtime-scope dependencies are not needed for compilation, only for
execution, such as JDBC (Java Database Connectivity) drivers. These dependencies will
be packaged in the final archive (e.g. will be packages in a War or Ear archive)
• test: Test-scope dependencies are needed only to compile and run tests (JUnit, for
example).

Lifecycle phases
Basic phases:
• 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.
These build phases (plus the other build phases not
shown here) are executed sequentially to complete
the default lifecycle.

Plugins
Core maven plugins:
 Compiler plugin
 Surefire plugin
 EJB plugin
 War plugin
 EAR plugin
Other plugins:
 Release plugin
 War overlay plugin
 Resources plugin
Plugins are downloaded and installed automatically, if not present on your local system, in
much the same way that a dependency is handled.
${home.repository}.m2repositoryorgapachemavenplugins
API for creating your own maven plugins.
http://maven.apache.org/plugin-developers/

Plugins – compiler plugin
Used to compile the source files
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>2.0</version>
<configuration>
<source>1.6</source>
<target>1.6</target>
</configuration>
</plugin>

Plugins – surefire plugin
Used to run Tests.
<plugin>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.12.2</version>
<configuration>
….
</configuration>
</plugin>
* Note that the Surefire plugin (which executes the test) looks for tests
contained in files with a particular naming convention. By default, the
following tests are included:
• **/*Test.java
• **/Test*.java
• **/*TestCase.java
* To execute one Test at a time, run mvn test -Dtest=MyUnitlTest

Plugins – ejb plugin
Used to create EJB artifacts
<plugin>
<artifactId>maven-ejb-plugin</artifactId>
<version>${maven.ejb.plugin.version}</version>
<configuration>
<ejbVersion>3.1</ejbVersion>
</configuration>
</plugin>
http://maven.apache.org/plugins/maven-ejb-plugin/

Plugins – war plugin
Used to create WAR artifacts
<plugin>
<artifactId>maven-war-plugin</artifactId>
<version>2.4</version>
<configuration>
<warSourceDirectory>webApplication</warSourceDirectory>
<packagingExcludes>WEB-INF/lib/*.jar</packagingExcludes>
</configuration>
</plugin>
http://maven.apache.org/plugins/maven-war-plugin/

Plugins – ear plugin
Used to create EAR artifacts
<plugin>
<artifactId>maven-ear-plugin</artifactId>
<configuration>
<displayName>myEAR</displayName>
<applicationName>myEAR</applicationName>

<generateApplicationXml>true</generateApplicationXml>
<defaultLibBundleDir>lib</defaultLibBundleDir>
<skinnyWars>true</skinnyWars>
<version>6</version>
<modules>
<ejbModule>
<groupId>com.manolis</groupId>
<artifactId>main</artifactId>
<bundleDir>/</bundleDir>
<bundleFileName>main.jar</bundleFileName>
</ejbModule>
<webModule>
<groupId>com.manolis</groupId>
<artifactId>web</artifactId>
<bundleFileName>web.war</bundleFileName>
<bundleDir>/</bundleDir>
<contextRoot>/web</contextRoot>
</webModule>
</modules>
</configuration>
</plugin>

Profiles
• Profiles are Maven's way of letting you create environmental variations in the build life
cycle to accommodate things like building on different platforms, building with different
JVMs, testing with different databases, or referencing the local file system. Typically you
try to encapsulate as much as possible in the POM to ensure that builds are portable, but
sometimes you simply have to take into consideration variation across systems and this is
why profiles were introduced in Maven.
• Profiles are specified using a subset of the elements available in the POM itself (plus one
extra section), and can be activated in several ways. Profiles modify the POM at build
time, and are meant to be used in complementary sets to give equivalent-but-different
parameters for a set of target environments (providing, for example, the path of the
application server root in the development, testing, and production environments).
• You can define profiles in one of the following three places:
• The Maven settings file (typically <your -home-directory>/.m2/settings.xml)
• A file in the the same directory as the POM, called profiles.xml
• The POM itself

IDE integration… (the problems
start here )
• All major IDEs have maven support
• Eclipse, IntelliJ, Netbeans
• BUT…
Potential problems :
• Auto publishing to application servers
• IDE warnings on maven projects

Useful maven commands
• mvn -version
• mvn clean This will remove the target directory
• mvn package
• mvn install
Installs the artifact (the JAR file) you've generated into your local repository. It can
then be used by other projects as a dependency. The directory <your-
homedirectory>/. m2/repository is the default location of the repository.
• mvn test
• mvn test -Dtest=MyUnitlTest
• mvn dependency:tree

Beyond Maven - The big picture
Continuous Integration Server (e.g. Jenkins)
Maven
Modules and dependencies
Build Testing
Code
Analysis
Deployment -
Integration
Artifact Repository (e.g. Nexus)
Caching Proxy for libraries Releases

References
o http://maven.apache.org/
o http://maven.apache.org/ref/3.1.0/maven-model/maven.html
o http://maven.apache.org/plugins/maven-war-plugin/examples/skinny-wars.html
o http://maven.apache.org/guides/introduction/introduction-to-the-
lifecycle.html#Lifecycle_Reference
o http://maven.apache.org/plugins/maven-ejb-plugin/
o http://maven.apache.org/maven-release/maven-release-plugin/
o http://maven.apache.org/plugin-developers/
o http://search.maven.org/
o http://eclipse.org/m2e/
o http://jenkins-ci.org/
o http://www.sonatype.org/nexus/
o http://www.javaworld.com/javaworld/jw-12-2005/jw-1205-maven.html
o http://www.ibm.com/developerworks/java/tutorials/j-mavenv2/section2.html
o “Better Builds with Maven” Vincent Massol & Jason van Zyl

Introduction to maven

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