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Mastering Apache Maven 3
Mastering Apache Maven 3

Mastering Apache Maven 3: Enhance developer productivity and address exact enterprise build requirements by extending Maven

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Mastering Apache Maven 3

Chapter 2. Demystifying Project Object Model

Project Object Model (POM) is at the heart of any Maven project. This chapter focuses on core concepts and best practices related to POM in building a large-scale, multimodule Maven project.

As we proceed with this chapter, we will be discussing the following topics:

  • The POM hierarchy, super POM, and parent POM
  • Extending and overriding POM files
  • Maven coordinates
  • Managing dependencies
  • Transitive dependencies
  • Dependency scopes and optional dependencies

    Note

    In Maven 1, the equivalent to today's pom.xml file was identified as project.xml. Maven 2 renamed it to pom.xml. More details about the POM are available at http://maven.apache.org/pom.html.

Project Object Model

Any Maven project must have a pom.xml file. POM is the Maven project descriptor, just like the web.xml file in your Java EE web application or the build.xml file in your Ant project. The following code lists out all the key elements in a Maven pom.xml file. As we proceed with the book, we will discuss how to use each element in the most effective manner:

<project>
  <parent>...</parent>
  <modelVersion>4.0.0</modelVersion>
  <groupId>...</groupId>
  <artifactId>...</artifactId>
  <version>...</version>
  <packaging>...</packaging>
   
   <name>...</name>
  <description>...</description>
  <url>...</url>   
  <inceptionYear>...</inceptionYear>
  <licenses>...</licenses>
  <organization>...</organization>
  <developers>...</developers>
  <contributors>...</contributors>


  <dependencies>.....

The POM hierarchy

POM files maintain a parent-child relationship between them. A child POM file inherits all the configuration elements from its parent POM file. This is how Maven sticks to its design philosophy, which is convention over configuration. The minimal POM configuration for any Maven project is extremely simple, which is as follows:

<project>
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.packt</groupId>
  <artifactId>sample-one</artifactId>
  <version>1.0.0</version>
</project>

Super POM

Any POM file can point to its parent POM. If the parent POM element is missing, then there is a system-wide POM file that is automatically treated as the parent POM file. This POM file is well known as the super POM. Ultimately, all the application POM files get extended from the super POM. The super POM file is at the top of the POM hierarchy, and it is bundled inside MAVEN_HOME/lib/maven-model-builder-3.2.3.jar - org/apache/maven/model/pom-4.0.0.xml. In Maven 2, this was bundled inside maven-2.X.X-uber.jar. All the default configurations are defined in the super POM file. Even the simplest form of a POM file will inherit all the configurations defined in the super POM file. Whatever configuration you need to override, you can do it by redefining the same section in your application POM file. The following lines of code show the super POM file configuration, which comes with Maven 3.2.3:

<project>
  <modelVersion>4.0.0</modelVersion>

The Maven central is the only...

POM extending and overriding

Let's see how POM overriding works. In the following example, we extend the repositories section to add one more repository to what is defined in the Maven super POM file:

<project>
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.packt</groupId>
  <artifactId>sample-one</artifactId>
  <version>1.0.0</version>

  <repositories>
    <repository>
      <id>wso2-nexus</id>
      <name>WSO2 internal Repository</name>
      <url>http://maven.wso2.org/nexus/content/groups/wso2-public/
      </url>
      <releases>
        <enabled>true</enabled>
        <updatePolicy>daily</updatePolicy>
        <checksumPolicy>ignore</checksumPolicy>
      </releases>
    </repository>
  </repositories>

</project>

Type the following command from the directory, where you have the previous POM file:

$ mvn help...

Maven coordinates

Maven coordinates identify uniquely a project, a dependency, or a plugin defined in POM. Each entity is uniquely identified by the combination of a group identifier, an artifact identifier, and the version (and, of course, with the packaging and the classifier). The group identifier is a way of grouping different Maven artifacts. For example, a set of artifacts produced by a company can be grouped under the same group identifier. The artifact identifier is the way you identify an artifact, which could be JAR, WAR, or any other type of an artifact uniquely within a given group. The version element lets you keep the same artifact in different versions in the same repository.

Note

A valid Maven POM file must have groupId, artifactId, and version. The groupId and the version elements can also be inherited from the parent POM file.

All these three coordinates of a given Maven artifact are used to define its path in the Maven repository. If we take the following example, the corresponding...

Project Object Model


Any Maven project must have a pom.xml file. POM is the Maven project descriptor, just like the web.xml file in your Java EE web application or the build.xml file in your Ant project. The following code lists out all the key elements in a Maven pom.xml file. As we proceed with the book, we will discuss how to use each element in the most effective manner:

<project>
  <parent>...</parent>
  <modelVersion>4.0.0</modelVersion>
  <groupId>...</groupId>
  <artifactId>...</artifactId>
  <version>...</version>
  <packaging>...</packaging>
   
   <name>...</name>
  <description>...</description>
  <url>...</url>   
  <inceptionYear>...</inceptionYear>
  <licenses>...</licenses>
  <organization>...</organization>
  <developers>...</developers>
  <contributors>...</contributors>


  <dependencies>...&lt...

The POM hierarchy


POM files maintain a parent-child relationship between them. A child POM file inherits all the configuration elements from its parent POM file. This is how Maven sticks to its design philosophy, which is convention over configuration. The minimal POM configuration for any Maven project is extremely simple, which is as follows:

<project>
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.packt</groupId>
  <artifactId>sample-one</artifactId>
  <version>1.0.0</version>
</project>

Super POM


Any POM file can point to its parent POM. If the parent POM element is missing, then there is a system-wide POM file that is automatically treated as the parent POM file. This POM file is well known as the super POM. Ultimately, all the application POM files get extended from the super POM. The super POM file is at the top of the POM hierarchy, and it is bundled inside MAVEN_HOME/lib/maven-model-builder-3.2.3.jar - org/apache/maven/model/pom-4.0.0.xml. In Maven 2, this was bundled inside maven-2.X.X-uber.jar. All the default configurations are defined in the super POM file. Even the simplest form of a POM file will inherit all the configurations defined in the super POM file. Whatever configuration you need to override, you can do it by redefining the same section in your application POM file. The following lines of code show the super POM file configuration, which comes with Maven 3.2.3:

<project>
  <modelVersion>4.0.0</modelVersion>

The Maven central is the only...

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Description

If you are working with Java or Java EE projects and you want to take full advantage of Maven in designing, executing, and maintaining your build system for optimal developer productivity, then this book is ideal for you. You should be well versed with Maven and its basic functionality if you wish to get the most out of the book.

What you will learn

  • Apply Maven best practices in designing a build system to improve developer productivity Customize the build process to suit your enterprise needs by developing custom Maven plugins, lifecycles, and archetypes Implement and deploy a Maven repository manager to manage the build process in a better and smoother way Design the build in a way that prevents any maintenance nightmares with proper dependency management Optimize Maven configuration settings Create your own distribution archive using Maven assemblies Build custom Maven lifecycles and lifecycle extensions

Product Details

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Publication date, Length, Edition, Language, ISBN-13
Publication date : Dec 29, 2014
Length: 298 pages
Edition : 1st
Language : English
ISBN-13 : 9781783983865
Vendor :
Apache
Tools :

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Product Details

Publication date : Dec 29, 2014
Length: 298 pages
Edition : 1st
Language : English
ISBN-13 : 9781783983865
Vendor :
Apache
Tools :

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Table of Contents

10 Chapters
1. Apache Maven Quick Start Chevron down icon Chevron up icon
2. Demystifying Project Object Model Chevron down icon Chevron up icon
3. Maven Configuration Chevron down icon Chevron up icon
4. Build Lifecycles Chevron down icon Chevron up icon
5. Maven Plugins Chevron down icon Chevron up icon
6. Maven Assemblies Chevron down icon Chevron up icon
7. Maven Archetypes Chevron down icon Chevron up icon
8. Maven Repository Management Chevron down icon Chevron up icon
9. Best Practices Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Full star icon Half star icon 4.3
(3 Ratings)
5 star 33.3%
4 star 66.7%
3 star 0%
2 star 0%
1 star 0%
Eri hamilton Otero Jan 12, 2024
Full star icon Full star icon Full star icon Full star icon Full star icon 5
This is a very good book! 100% recommended
Amazon Verified review Amazon
Marek Wieczorek Feb 17, 2016
Full star icon Full star icon Full star icon Full star icon Empty star icon 4
As a Maven newbie, I feel I learned a lot from the book.
Amazon Verified review Amazon
Marcos May 02, 2015
Full star icon Full star icon Full star icon Full star icon Empty star icon 4
Good book. Very complete. It is not a cookbook style. It is more like a complete reference
Amazon Verified review Amazon
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