Maven overview

Maven for AMPer - An Overview
By Yukti Kaura

The Intent
2

The intent of this presentation is to clarify the understanding of how
Maven is integrated with AMPer. During the course of this
presentation the focus would be to answer the following basic
questions
THE BASICS
• What is Maven?
• What is Maven to AMPer: Case Study?
• What does the Maven site contain?
• What are the External Maven Tools used in Eclipse?

DIVING DEEPER
• What is settings.xml?
• What is pom.xml?

Maven for AMPer - An Overview | CONFIDENTIAL 2008 December 13, 2012

What is Maven ?
3

• MAVEN – is a project management tool.
• It provides a superset of features found in a build tool
such as ANT.
• In addition to providing build capabilities- used to
build deployable artifacts from source code, Maven
can also run reports, generate a web site etc…
• More formally,
Maven is a project management tool which
encompasses a project object model,
a set of standards, a project lifecycle,
a dependency management system, and logic for
executing plugin goals at defined phases in a
lifecycle. When you use Maven, you describe your
project using a well-defined project object model .


Project Lifecycle
4

http://maven.apache.org/plugins/index.html

Plugin goals in defined phases of a lifecycle
5

Plugin contains goals

Bound Goals are Run when
Their Phases Execute

Standard Directory Layout of Maven
6

src/main/java Application/Library sources

src/main/resources Application/Library resources

src/main/filters Resource filter files

src/main/assembly Assembly descriptors

src/main/config Configuration files

src/main/webapp Web application sources

src/test/java Test sources

src/test/resources Test resources

src/test/filters Test resource filter files

src/site Site

LICENSE.txt Project's license

README.txt Project's readme

Benefits of
Standards

Dependency Management 7

Project A depends on projects B and A
C. Project B depends on project D,
and project C depends on project E.
The full set of direct and transitive
dependencies for project A would be C
projects B, C, D, and E, but all
B
project A had to do was define a
dependency on B and C.

Transitive dependencies can come D E
in handy when your project relies on
other projects with several small
dependencies (like Hibernate,
Apache Struts, or the Spring You just tell Maven which
Framework). libraries you need, and Maven
will take care of the libraries
that your libraries need (and
so on).


Maven Coordinates 8

pom.xml

Maven Space is a coordinate system of projects


Maven Repository
9

Maven ships with the bare minimum and fetches from a
remote repository when it needs to. Maven ships with a
default remote repository location
(http://repo1.maven.org/maven2) which it uses to
download the core Maven plugins and dependencies.

Maven repositories are both a local cache of artifacts
downloaded from a remote repository and a mechanism
for allowing your projects to depend on each
other.


How is Maven used in AMPer?
10

• Making the build process easy

• Providing quality project information
» Unit test reports including coverage

• Providing guidelines for best practices development
E.g. Source code is assumed to be in $
{basedir}/src/main/java and resources are assumed to be in $
{basedir}/src/main/resources. Tests are assumed to be in $
{basedir}/src/test, and a project is assumed to produce
a JAR file. Which version of
Maven are we
• Coherent site of project information: Using the same using? Maven 2.0
metadata as for the build process, Maven is able to
generate a web site

• Maven also assists in project workflow such as
release management.
» Maven integrates with source control system SVN and
manages the release of a project.


What does the Maven site contain? 11

AirMessenger Personal project report

This report contains information about JUnit, FindBugs and CheckStyle.It
also contains data about The Lines Of Code, Change Log, Build Log and
% Code Coverage.
This is an example of the continuous integration system used by the
project.

http://maven.apache.org/plugins/index.html Links


12

What are the External Maven Tools used in Eclipse?


What are the External Maven Tools used in Eclipse? 13

• Maven 2 install
This tool builds all the modules, and installs it in the local repository. The local repository
is created in your home directory (or alternative location that you created it), and is the
location where all downloaded binaries and the projects you built are stored. When you
run install, Maven will copy the each project's main artifact and each assembly to your
local Maven repository. All of these artifacts are now available for reference as
dependencies in other projects locally.
Sample output after running the tool


14

• Maven 2 Clean
This tool deletes the output of a build by deleting the build directory. If you
haven't customized the location of the build directory it will be the $
{basedir}/target directory as defined by the Super POM.
Sample output after running the tool


15

STOP & PONDER


16

Settings.xml


settings.xml
17

Settings in this file are settings which apply to many <settings>
<localRepository/>
projects and which should not be bundled to any <interactiveMode/>
specific project, or distributed to an audience. These <usePluginRegistry/
>
include values such as the local repository location, <offline/>
alternate remote repository servers, and <pluginGroups/>
authentication information. Location where <servers/>
<mirrors/>
a settings.xml file may live: <proxies/>
» User-specific Settings File: ~/.m2/settings.xml <profiles/>
<activeProfiles/>
</settings>
The settings element in the settings.xml file contains
elements used to define values which configure
Maven execution


Settings.xml - Piece by Piece
18

SERVERS
The distributionManagement element of the POM defines the repositories for
deployment. However, certain settings such as security credentials should not be
distributed along with the pom.xml. This type of information should exist on the build
server in the settings.xml.
<servers>
<server>
<username>maven</username> These elements appear as a pair denoting the login
<password>maven</password> and password required to authenticate to this server.

<id>firsthop</id> This is the id of the server (not of the user to login as) that
matches the distributionManagement repository element's id
</server>
</servers>

MIRRORS
<mirrors>
<mirror>
<id>standalone.repository</id> - The unique identifier of this mirror
<url>file:///C:/AlexandriaPlatformSDK/bin/../m2_fhrepository</url> The base URL of this mirror.
<mirrorOf>central</mirrorOf> The id of the server that this is a mirror of.
For example, to point to a mirror of the Maven central server
(http://repo1.maven.org/maven2), set this element to central.
</mirror>
</mirrors>


settings.xml
19

PROFILES

The profile element in the settings.xml is a truncated version of the pom.xml
profile element. It consists of the
• activation,
• repositories,
• pluginRepositories
• and properties elements.
The profile elements only include these four elements because they
concern themselves with the build system as a whole (which is the role of
the settings.xml file), not about individual project object model settings.
If a profile is active from settings, its values will override any equivalent
profiles which matching identifiers in a POM.
PROFILES - >REPOSITORIES
Repositories are remote collections of projects from which Maven uses to
populate the local repository of the build system. It is from this local
repository that Maven calls it plugins and dependencies. Different remote
repositories may contain different projects, and under the active profile
they may be searched for a matching release or snapshot artifact.


settings.xml
20

Snapshot and Release These are the policies for each type of artifact, Release or
snapshot. With these two sets, a POM has the power to alter the policies for each
type independent of the other within a single repository. For example, one may
decide to enable only snapshot downloads, possibly for development purposes.

<repository>
<snapshots>
<enabled>true</enabled> true or false for whether this repository is enabled for the
respective type (releases or snapshots)
<updatePolicy>always</updatePolicy> This element specifies how often updates should attempt
to occur. Maven will compare the local POMs timestamp to the remote. The choices are:
always, daily (default), interval:X (where X is an integer in minutes) or never.
</snapshots>
<releases>
<enabled>true</enabled>
<updatePolicy>always</updatePolicy>
</releases>
<id>firsthop</id>
<name>Airwide Solutions Maven Repository</name>
<url>http://maven.alexmontreal.airwidesolutions.com/maven/repository2</url>
</repository>


settings.xml
21

PROFILES -> PLUGIN REPOSITORIES
Repositories are home to two major types of artifacts. The first are
artifacts that are used as dependencies of other artifacts. The
other type of artifact is plugins. Maven plugins are themselves a
special type of artifact. Because of this, plugin repositories are
separated from other repositories. The structure of the
pluginRepositories element block is similar to the repositories
element. The pluginRepository elements each specify a remote
location of where Maven can find new plugins

ACTIVE PROFILES

The final piece of the settings.xml puzzle is
the activeProfiles element. This contains a set of active profile
elements, which each have a value of a profile id. Any profile id
defined as an activeProfile will be active, regardless of any
environment settings

<activeProfiles>
<activeProfile>firsthopDefault</activeProfile>
</activeProfiles>


22

STOP & PONDER


23

Pom.xml


What is a POM?
24

• A Project Object Model or POM
is the fundamental unit of work
in Maven. It is an XML file that
contains information about the
project and configuration
details used by Maven to build
the project. It contains default
values for most projects.
Examples for this is the build
directory, which is target; the
source directory, which
is src/main/java; the test source
directory, which is src/main/test

• Maven projects, dependencies,
builds, artifacts: all of these are The Project Object Model
objects to be modeled and
described. These objects are
described by an XML file called
a Project Object Model .


The Super POM 26

• All Maven project POMs extend the Super POM which
defines a set of defaults shared by all projects.
• The Super POM defines some standard configuration
variables that are inherited by all projects.
The default Super POM defines a single remote Maven
repository with an ID of central

• The central Maven repository also contains Maven
plugins. The default plugin repository is the central Maven
repository.

• The build element sets the default values for directories in
the Maven Standard Directory layout .i.e. it specifies the
default directory structure.


Maven Coordinate 27

<project>
<modelVersion>4.0.0</modelVersion> - Current model version should be set to 4.0.0
<groupId>com.mycompany.app</groupId>
<artifactId>my-app</artifactId>
<version>1</version>
</project>

Maven Coordinate is made up of three components. These three values form the project's fully qualified
artifact name. This is in the form of <groupId>:<artifactId>:<version>

groupId
A groupId groups a set of related artifacts. Group identifiers generally resemble a Java package
name.
e.g. com.airwidesolutions.amper

artifactId
The artifactId is the project's main identifier. When you generate an artifact, this artifact is
going to be
named with the artifactId. e.g. amper.build

version
When an artifact is released, it is released with a version number. This version number is an
identifier of the form <major version>.<minor version>.<incremental version>-
<qualifier> such as "1.1.2-alpha-01". We can also use a snapshot version. A snapshot version
is a version for a component which is under development, snapshot version numbers always end
in SNAPSHOT; for example, "1.0-SNAPSHOT“.Maven will expand SNAPSHOT token to a date and
time value converted to UTC (Coordinated Universal Time) e.g. 1.0-20080207-230803-1 .


Project Inheritance
28

• The following slides deal with 3 scenarios as examples and the variation in the
definition of pom.xml in each case
• Example 1
Let us specify their directory structure as this

Let us reuse our previous artifact, com.mycompany.app:my-app:1 as displayed in the
previous slide. Now, if we were to turn com.mycompany.app:my-app:1 into a parent
artifact of com.mycompany.app:my-module:1,we will have to modify
com.mycompany.app:my-module:1's POM to the following configuration:

<project>
<parent> Notice that we now have an added
<groupId>com.mycompany.app</groupId> section, the parent section. This
<artifactId>my-app</artifactId> section allows us to specify which
<version>1</version> artifact is the parent of our POM.
</parent>
<modelVersion>4.0.0</modelVersion>
Alternatively, if we want the groupId
<artifactId>my-module</artifactId>
and / or the version of your modules to
<version>1</version> be the same as their parents, you can
</project> remove the groupId and / or the version
identity of your module in its POM.


Project Aggregation
29

• Project Aggregation is similar to Project Inheritance. But instead of specifying the
parent POM from the module, it specifies the modules from the parent POM. By doing
so, the parent project now knows its modules, and if a Maven command is invoked
against the parent project, that Maven command will then be executed to the parent's
modules as well. To do Project Aggregation, you must do the following:

• Change the parent POMs packaging to the value "pom" .
• Specify in the parent POM the directories of its modules (children POMs)

<project>
In the revised com.mycompany.app:my-app:1, the
packaging section and the modules sections were
added. For the packaging, it's value was set to "pom", and
for the modules section, we have the element
<version>1</version> <module>my-module</module>.
<packaging>pom</packaging>
The value of <module> is the relative path from the
com.mycompany.app:my-app:1 to
<modules>
com.mycompany.app:my-module:1's POM (by practice,
<module>my-module</module>
we use the module's artifactId as the module directory's
</modules>
name).
</project>


30
Project Inheritance vs Project Aggregation

INHERITANCE

• If you have several Maven projects, and they all have similar configurations, you can
refactor your projects by pulling out those similar configurations and making a
parent project. Thus, all you have to do is to let your Maven projects inherit that
parent project, and those configurations would then be applied to all of them.

AGGREGATION
• And if you have a group of projects that are built or processed together, you can
create a parent project and have that parent project declare those projects as its
modules. By doing so, you'd only have to build the parent and the rest will follow.

• But of course, you can have both Project Inheritance and Project Aggregation.
Meaning, you can have your modules specify a parent project, and at the same time,
have that parent project specify those Maven projects as its modules. You'd just
have to apply all three rules:

• Specify in every child POM who their parent POM is.
• Change the parent POMs packaging to the value "pom" .
• Specify in the parent POM the directories of its modules (children POMs)


Example 3
31

To do both project inheritance and aggregation, you only have to apply
all three rules.
com.mycompany.app:my-app:1's POM

<project>
<packaging>pom</packaging>
<modules>
<module>../my-module</module>
</modules>
</project>
com.mycompany.app:my-module:1's POM

<project>
<parent>
<relativePath>../parent/pom.xml</relativePath>
</parent>
<artifactId>my-module</artifactId>
</project>

Dependency Management
32

• Maven can manage both internal and external dependencies. An external dependency
for a Java project might be a library such as Log4J. An internal dependency is
illustrated by a web application project depending on another project that contains
service classes, model objects, or persistence logic .
Dependency Scope
• Scope controls which dependencies are available in which classpath, and which
dependencies are included with an application .
• compile
compile is the default scope; all dependencies are compile-scoped if a scope is not
supplied. compile dependencies are available in all classpaths.Furthermore, those
dependencies are propagated to dependent projects.
• provided
provided dependencies are used when you expect the JDK or a container to provide.
provided dependencies are available on the compilation classpath (not runtime).
• runtime
runtime dependencies are required to execute and test the system, but they are not
required for compilation
• test
test -scoped dependencies are not required during the normal operation of an
application, and they are available only during test compilation and execution phases


Example from ldap/pom.xml
33

<dependencies>
<dependency>
<groupId>com.firsthop.wb2</groupId>
<artifactId>wb2.platform.nnapi</artifactId>
<scope>provided</scope>
</dependency>
<dependency>
<artifactId>wb2.platform.nnapi</artifactId>
<type>test-jar</type>
<scope>provided</scope>
</dependency>
<dependency>
<artifactId>wb2.platform.mndeploy</artifactId>
<scope>compile</scope>
</dependency>
</dependencies>


Dependency Management
34

• The dependency management section is a mechanism for centralizing dependency
information. When you have a set of projects that inherits a common parent it's
possible to put all information about the dependency in the common POM and have
simpler references to the artifacts in the child POMs.

• Maven provides a way for you to consolidate dependency version numbers in the
dependencyManagement element. You'll usually see the
dependencyManagement element in a top-level parent POM for an organization or
project. Using the dependencyManagement element in a pom.xml allows you to
reference a dependency in a child project without having to explicitly list the version.
Maven will walk up the parent-child hierarchy until it finds a project with a
dependencyManagement element, it will then use the version specified in this
dependencyManagement element.

• Default dependency information for projects that inherit from this one. The
dependencies in this section are not immediately resolved. Instead, when a POM
derived from this one declares a dependency described by a matching groupId and
artifactId, the version and other values from this section are used for that
dependency if they were not already specified.


Example
35

For example, if you have a large set of projects which make use of the
amper.personalservicelogic.api version 0.0.7, you could define the following
dependencyManagement element in your multi-module project's top-level POM.
<dependencyManagement>
<dependencies>
<dependency>
<groupId>com.airwidesolutions.amper</groupId>
<artifactId>amper.personalservicelogic.api</artifactId>
<version>0.0.7</version>
</dependency>
<dependencies>
</dependencyManagement>
Then, in a child project, you can add a dependency to the amper.personalservicelogic.api
using the following dependency XML:
<dependencies>
<dependency>
<groupId>com.airwidesolutions.amper</groupId>
<artifactId>amper.personalservicelogic.api</artifactId>
</dependency>
<dependencies>
The child project did not have to explicitly list the version of
the amper.personalservicelogic.api dependency. Because this dependency was defined in the
top-level POM's dependencyManagement element, the version number is going to propagate to
the child project's dependency


Build tag
36

The <build> element contains informations required to build the project.
<build>
<plugins> The list of plugins to use.
<plugin>
<artifactId>maven-release-plugin</artifactId>
<configuration>
<tagBase>https://svn.alexmontreal.airwidesolutions.com/svn/repository
/amper/selfprovisioning/tags</tagBase>
</configuration>
</plugin>
</plugins>
<testResources> This element describes all of the classpath resources such as
properties files associated with a project's unit tests.
<testResource>
<filtering>true</filtering> Whether resources are filtered to replace tokens
with parameterised values or not. The
values are taken from the properties element

<directory>${basedir}/src/test/resources</directory>
Describe the directory where the resources are stored.

<includes>
<include>**/wb2.xml</include> A list of patterns to include, e.g. **/*.xml.
</includes>
</testResource>
</testResources>
</build>

SCM tag
37

The <scm> element contains informations required to the SCM (Source Control
Management) of the project.

<scm>
<connection>scm:svn:https://svn.alexmontreal.airwidesolutions.com/svn/repository/amper/selfprovi
sioning/trunk</connection>
The source control management system URL that describes the repository and how
and how to connect to the repository.
Note :- The SCM we use is SubVersioN which is among the fully implemented SCM of
Maven

<developerConnection>scm:svn:https://svn.alexmontreal.airwidesolutions.com/svn/repository/amper/sel
fprovisioning/trunk</developerConnection>
Just like connection, but for developers, i.e. this scm connection will not be read
only.
<url>https://svn.alexmontreal.airwidesolutions.com/svn/repository/amper/selfprovisioning/trunk</url>
The URL to the project's browsable SCM repository
</scm>


Distribution Management
38

This element describes all that pertains to distribution for a project. It is primarily used for
deployment of artifacts and the site produced by the build.

<distributionManagement>
<repository> Information needed to deploy the artifacts generated by the project
to a remote repository
<id>firsthop</id> A unique identifier for a repository. This is used to match
the repository to configuration in the settings.xml file
<name> Airwide Solutions Maven Repository</name> Human readable name
of the repository.
<url>
scp://maven.alexmontreal.airwidesolutions.com/srv/maven/repository2</url>
The url of the repository, in the form protocol://hostname/path.
</repository>
</distributionManagement>


39

STOP & PONDER


References
40

• http://maven.apache.org/ref/current/maven-
model/maven.html#class_DependencyManagement
• http://www.sonatype.com/book/reference/public-
book.html
• http://maven.apache.org/guides/


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