Editing Apache Maven

{{Short description|Software tool for managing build dependencies}}
{{Infobox software
| name = Apache Maven
| logo = Apache Maven logo.svg
| developer = [[The Apache Software Foundation]]
| released = {{Start date and age|df=yes|2004|07|13}}
| discontinued = No
| latest release version = {{wikidata|property|preferred|references|edit|P348|P548=Q2804309}}                                             | latest release date    = {{Start date and age|{{wikidata|qualifier|preferred|single|P348|P548=Q2804309|P577}}|df=yes}}
| programming language = [[Java (programming language)|Java]]
| genre = [[Build tool]]
| license = [[Apache License 2.0]]
| website = {{URL|https://maven.apache.org}}
}}
'''Maven''' is a [[build automation]] tool used primarily for [[Java (programming language)|Java]] projects. Maven can also be used to build and manage projects written in [[C Sharp (programming language)|C#]], [[Ruby (programming language)|Ruby]], [[Scala (programming language)|Scala]], and other languages. The Maven project is hosted by [[The Apache Software Foundation]], where it was formerly part of the [[Jakarta Project]].

Maven addresses two aspects of building software: how software is [[Software build|built]] and its dependencies. Unlike earlier tools like [[Apache Ant]], it uses conventions for the build procedure. Only exceptions need to be specified. An [[XML]] file describes the software project being built, its dependencies on other external modules and components, the build order, directories, and required [[Plug-in (computing)|plug-ins]]. It comes with pre-defined targets for performing certain well-defined tasks such as compilation of code and its packaging. Maven dynamically downloads [[Java (programming language)|Java]] libraries and Maven plug-ins from one or more repositories such as the Maven 2 Central Repository, and stores them in a local cache.<ref name="maven2repo">{{cite web|url=http://repo1.maven.org/maven2/|title=Index of /maven2/|access-date=2009-04-15|archive-url=https://web.archive.org/web/20180917061140/http://repo1.maven.org/maven2/|archive-date=2018-09-17|url-status=dead}}</ref> This local cache of downloaded [[Artifact (software development)|artifacts]] can also be updated with artifacts created by local projects. Public repositories can also be updated.

Maven is built using a plugin-based architecture that allows it to make use of any application controllable through standard input. A [[C (programming language)|C]]/[[C++]] native plugin is maintained for Maven 2.<ref>{{cite web|url=http://www.mojohaus.org/maven-native/native-maven-plugin/|title=MojoHaus Native Maven Plugin|first=Trygve|last=Laugstol}}</ref>

Alternative technologies like [[Gradle]] and [[sbt (software)|sbt]] as build tools do not rely on [[XML]], but keep the key concepts Maven introduced. With [[Apache Ivy]], a dedicated dependency manager was developed as well that also supports Maven repositories.<ref>{{Cite web|url=https://ant.apache.org/ivy/history/2.2.0/resolver/ibiblio.html|title=IBiblio Resolver &#124; Apache Ivy™}}</ref>

Apache Maven has support for [[reproducible build]]s.<ref>{{Cite web|url=https://cwiki.apache.org/confluence/pages/viewpage.action?pageId=74682318|title=Reproducible/Verifiable Builds - Apache Maven - Apache Software Foundation|website=cwiki.apache.org}}</ref><ref>{{Cite web|url=https://dzone.com/articles/reproducible-builds-in-java|title=Reproducible Builds in Java - DZone Java|website=dzone.com}}</ref>

== History ==
[[File:Maven repository artifact growth.png|thumb|The number of artifacts on Maven's central repository has grown rapidly in the past]]

Maven was created by Jason van Zyl in 2002 and began as a sub-project of [[Apache Turbine]]. In 2003 Maven was accepted as a top level [[Apache Software Foundation]] project.

Version history:

* ''Version 1'' - July 2004 - first critical milestone release (now at end of life).
* ''Version 2'' - October 2005 - after about six months in beta cycles (now at end of life).
* ''Version 3'' - October 2010 - remains mostly backwards compatible with Maven 2 projects. Changes included re-working core Project Builder and support for parallel builds. The re-working of the core decoupled file-based and in-memory representation and allowed add-ons to leverage non-XML based project definition files. Languages suggested include [[Ruby (programming language)|Ruby]] (already in private prototype by Jason van Zyl), [[YAML]], and [[Groovy (programming language)|Groovy]]. The parallel build feature leverages a configurable number of cores on a multi-core machine and especially suited for large multi-module projects.
* ''Version 4'' - currently in beta development (as of May 2024).

== Syntax ==
Maven projects are configured using a [[#Project Object Model|Project Object Model (POM)]] in a <code>pom.xml</code> file.

Example file:

<syntaxhighlight lang="xml">
<project>
  <!-- model version is always 4.0.0 for Maven 2.x POMs -->
  <modelVersion>4.0.0</modelVersion>
  
  <!-- project coordinates, i.e. a group of values which uniquely identify this project -->
  <groupId>com.mycompany.app</groupId>
  <artifactId>my-app</artifactId>
  <version>1.0</version>

  <!-- library dependencies -->
  <dependencies>

      <!-- The coordinates of a required library.
           The scope is 'test' to indicate the library
           is only used for running tests. -->
      <dependency>
          <groupId>org.junit.jupiter</groupId>
          <artifactId>junit-jupiter-engine</artifactId>
          <version>5.9.1</version>
          <scope>test</scope>
      </dependency>

  </dependencies>
</project>
</syntaxhighlight>

This POM defines a unique identifier for the project (''coordinates'') and a single dependency on the [[JUnit]] library. However, that is already enough for building the project and running the [[Unit testing|unit tests]] associated with the project. Maven accomplishes this by embracing the idea of [[Convention over Configuration]], that is, Maven provides default values for the project's configuration.

The directory structure of a normal [[Programming idiom|idiomatic]] Maven project has the following directory entries:
[[file:Maven CoC.svg|thumb|A directory structure for a Java project auto-generated by Maven]]
{| class="wikitable"
|-
! Directory name
! Purpose
|-
| project home
| Contains the <code>pom.xml</code> and all subdirectories.
|-
| <code>src/main/java</code>
| Contains the deliverable Java source code for the project.
|-
| <code>src/main/resources</code>
| Contains the deliverable resources for the project, such as property files.
|-
| <code>src/test/java</code>
| Contains the testing Java sourcecode (JUnit or TestNG test cases, for example) for the project.
|-
| <code>src/test/resources</code>
| Contains resources necessary for testing.
|}

The command <code>mvn package</code> will compile all the Java files, run any tests, and package the deliverable code and resources into <code>target/my-app-1.0.jar</code> (assuming the artifactId is my-app and the version is 1.0.)

Using Maven, the user provides only configuration for the project, while the configurable plug-ins do the actual work of compiling the project, cleaning target directories, running unit tests, generating API documentation and so on. In general, users should not have to write plugins themselves. Contrast this with [[Apache Ant|Ant]] and [[make (software)|make]], in which one writes imperative procedures for doing the aforementioned tasks.

== Design ==

=== Project Object Model ===
A Project Object Model (POM) <ref>[https://maven.apache.org/pom.html POM Reference]
</ref> provides all the configuration for a single project. General configuration covers the project's name, its owner and its dependencies on other projects. One can also configure individual phases of the build process, which are implemented as [[plug-in (computing)|plugin]]s. For example, one can configure the compiler-plugin to use Java version 1.5 for compilation, or specify packaging the project  even if some unit tests fail.

Larger projects should be divided into several modules, or sub-projects, each with its own POM. One can then write a root POM through which one can compile all the modules with a single command. POMs can also inherit configuration from other POMs. All POMs inherit from the Super POM<ref>[https://maven.apache.org/guides/introduction/introduction-to-the-pom.html#Super_POM Super POM]
</ref> by default. The Super POM provides default configuration, such as default source directories, default plugins, and so on.

=== Plug-ins ===
Most of Maven's functionality is in [[plug-in (computing)|plug-in]]s. A plugin provides a set of goals that can be executed using the command <code>mvn [plugin-name]:[goal-name]</code>. For example, a Java project can be compiled with the compiler-plugin's compile-goal<ref>{{cite web|url=https://maven.apache.org/plugins/maven-compiler-plugin/|title=Apache Maven Compiler Plugin – Introduction|first=Edwin|last=Punzalan}}</ref> by running <code>mvn compiler:compile</code>.

There are Maven plugins for building, testing, source control management, running a web server, generating [[Eclipse (software)|Eclipse]] project files, and much more.<ref>{{cite web|url=https://maven.apache.org/plugins/index.html|title=Maven – Available Plugins|first=Brett Porter Jason van Zyl Dennis Lundberg Olivier Lamy Benson Margulies Karl-Heinz|last=Marbaise}}</ref> Plugins are introduced and configured in a <plugins>-section of a <code>pom.xml</code> file. Some basic plugins are included in every project by default, and they have sensible default settings.

However, it would be cumbersome if the archetypal build sequence of building, testing and packaging a software project required running each respective goal manually:

* <code>mvn compiler:compile</code>
* <code>mvn surefire:test</code>
* <code>mvn jar:jar</code>

Maven's lifecycle concept handles this issue.

Plugins are the primary way to extend Maven. Developing a Maven plugin can be done by extending the org.apache.maven.plugin.AbstractMojo class. Example code and explanation for a Maven plugin to create a cloud-based virtual machine running an application server is given in the article ''Automate development and management of cloud virtual machines''.<ref>{{Cite journal| last=Amies| first=Alex|author2=Zou P X |author3=Wang Yi S | title=Automate development and management of cloud virtual machines|journal=IBM DeveloperWorks|publisher=IBM|date=29 Oct 2011| url=http://www.ibm.com/developerworks/cloud/library/cl-automatecloud/index.html}}</ref>

=== Build lifecycles ===
The build lifecycle is a list of named ''phases'' that can be used to give order to goal execution. One of Maven's three standard lifecycles is the ''default lifecycle'', which includes the following phases, performed in the order listed:<ref>{{cite web|url=https://maven.apache.org/guides/introduction/introduction-to-the-lifecycle.html#Lifecycle_Reference|title=Maven – Introduction to the Build Lifecycle|first=Brett|last=Porter}}</ref>

* validate
* generate-sources
* process-sources
* generate-resources
* process-resources
* compile
* process-test-sources
* process-test-resources
* test-compile
* test
* package
* install
* deploy

Goals provided by plugins can be associated with different phases of the lifecycle. For example, by default, the goal <code>compiler:compile</code> is associated with the <code>compile</code> phase, while the goal <code>surefire:test</code> is associated with the <code>test</code> phase. When the <code>mvn test</code> command is executed, Maven runs all goals associated with each of the phases up to and including the <code>test</code> phase. In such a case, Maven runs the <code>resources:resources</code> goal associated with the <code>process-resources</code> phase, then <code>compiler:compile</code>, and so on until it finally runs the <code>surefire:test</code> goal.

Maven also has standard phases for cleaning the project and for generating a project site. If cleaning were part of the default lifecycle, the project would be cleaned every time it was built. This is clearly undesirable, so cleaning has been given its own lifecycle.

Standard lifecycles enable users new to a project the ability to accurately build, test and install every Maven project by issuing the single command <code>mvn install</code>. By default, Maven packages the POM file in generated JAR and WAR files. Tools like diet4j<ref>{{cite web|url=http://diet4j.org/|title=diet4j - put Java JARs on a diet, and load maven modules as needed}}</ref> can use this information to recursively resolve and run Maven modules at run-time without requiring an "uber"-jar that contains all project code.

=== Dependencies ===
A central feature in Maven is [[Dependency (project management)|dependency management]]. Maven's dependency-handling mechanism is organized around a coordinate system identifying individual artifacts such as software libraries or modules. The POM example above references the JUnit coordinates as a direct dependency of the project. A project that needs, say, the [[Hibernate (Java)|Hibernate]] library simply has to declare Hibernate's project coordinates in its POM. Maven will automatically download the dependency and the dependencies that Hibernate itself needs (called [[Transitive dependency|transitive dependencies]]) and store them in the user's local repository. Maven 2 [https://search.maven.org/ Central Repository]<ref name="maven2repo"/> is used by default to search for libraries, but one can configure the repositories to be used (e.g., company-private repositories) within the POM.

The fundamental difference between Maven and Ant is that Maven's design regards all projects as having a certain structure and a set of supported task work-flows (e.g., getting resources from source control, compiling the project, unit testing, etc.). While most software projects in effect support these operations and actually do have a well-defined structure, Maven requires that this structure and the operation implementation details be defined in the POM file. Thus, Maven [[Convention over configuration|relies on a convention]] on how to define projects and on the list of work-flows that are generally supported in all projects.<ref>{{cite web|title=Maven: The Complete Reference |url=http://www.sonatype.com/books/mvnref-book/reference/installation-sect-compare-ant-maven.html |publisher=Sonatype |access-date=11 April 2013 |url-status=dead |archive-url=https://web.archive.org/web/20130421060027/http://www.sonatype.com/books/mvnref-book/reference/installation-sect-compare-ant-maven.html |archive-date=21 April 2013 }}</ref>

There are search engines such as The Central Repository Search Engine,<ref>[https://search.maven.org/ The Central Repository Search Engine]</ref> which can be used to find out coordinates for different open-source libraries and frameworks.

Projects developed on a single machine can depend on each other through the local repository. The local repository is a simple folder structure that acts both as a cache for downloaded dependencies and as a centralized storage place for locally built artifacts. The Maven command <code>mvn install</code> builds a project and places its binaries in the local repository. Then, other projects can utilize this project by specifying its coordinates in their POMs.

== Interoperability ==
Add-ons to several popular [[integrated development environment|integrated development environments (IDE)]] targeting the Java programming language exist to provide integration of Maven with the IDE's build mechanism and source editing tools, allowing Maven to compile projects from within the IDE, and also to set the classpath for code completion, highlighting compiler errors, etc.

Examples of popular IDEs supporting development with Maven include:

* [[Eclipse (software)|Eclipse]]
* [[NetBeans]]
* [[IntelliJ IDEA]]
* [[JBuilder]]
* [[JDeveloper]] (version 11.1.2)
* [[MyEclipse]]
* [[Visual Studio Code]]

These add-ons also provide the ability to edit the POM or use the POM to determine a project's complete set of dependencies directly within the IDE.

Some built-in features of IDEs are forfeited when the IDE no longer performs compilation. For example, Eclipse's JDT has the ability to recompile a single Java source file after it has been edited. Many IDEs work with a flat set of projects instead of the hierarchy of folders preferred by Maven. This complicates the use of [[Software configuration management|SCM]] systems in IDEs when using Maven.<ref>{{cite web|url=https://maven.apache.org/eclipse-plugin.html |title=maven.apache.org/eclipse-plugin.html |url-status=dead |archive-url=https://web.archive.org/web/20150507014621/http://maven.apache.org/eclipse-plugin.html |archive-date=May 7, 2015 }}</ref><ref>{{cite web|url=http://www.jetbrains.com/idea/features/ant_maven.html#Maven_Integration|title=IntelliJ IDEA :: Features|access-date=2009-09-02|archive-date=2015-05-24|archive-url=https://web.archive.org/web/20150524203728/http://www.jetbrains.com/idea/features/ant_maven.html#Maven_Integration|url-status=dead}}</ref><ref>{{cite web|url=http://wiki.netbeans.org/MavenBestPractices|title=MavenBestPractices - NetBeans Wiki|access-date=2009-09-02|archive-date=2018-01-14|archive-url=https://web.archive.org/web/20180114021502/http://wiki.netbeans.org/MavenBestPractices|url-status=dead}}</ref>

== See also ==
{{Portal|Free and open-source software}}
* [[Apache Continuum]] ''(discontinued)''
* [[Apache Jelly]]
* [[Hudson (software)|Hudson]] ''(discontinued)''
* [[Jenkins (software)|Jenkins]]
* [[List of build automation software]]
* [[Sonatype Nexus]]

== References ==
{{Reflist|30em}}

== Further reading ==
* {{ cite web | last=O'Brien | first=Tim | title=Maven: The Complete Reference | url=http://www.sonatype.com/books/mvnref-book/reference/ | work=Sonatype.com | publisher=Sonatype | access-date=15 March 2013 | display-authors=etal}}
* {{ cite book | others = Sonatype Company | title = Maven: The Definitive Guide | url = https://books.google.com/books?id=cBvZ4s72Z0gC | access-date = 2013-04-17 | year = 2009 | publisher = O'Reilly Media, Inc. | isbn = 9780596551780 | pages = 470 }}
* {{citation | first = Jason | last = Van Zyl | title = Maven: Definitive Guide | date = 2008-10-01 | edition = first | publisher = [[O'Reilly Media]] | pages = [https://archive.org/details/isbn_9780596517335/page/468 468] | isbn = 978-0-596-51733-5 | url = https://archive.org/details/isbn_9780596517335/page/468 | url-access = registration }}
* {{ cite book | title= JUnit in Action | publisher= [[Manning Publications]] | chapter= Running JUnit tests from Maven2 | year= 2011 | edition= 2nd | isbn= 978-1-935182-02-3 | pages= 152–168 }}
* {{ cite book | title= Maven Build Customization | publisher= Packt | year= 2013 | isbn= 9781783987221 | pages= 1–250 }}
* {{ cite book | title= Mastering Apache Maven 3 | url= https://www.packtpub.com/application-development/mastering-apache-maven-3 | publisher= Packt | year= 2014 | isbn= 9781783983865 | pages= 298 }}

== External links ==
* {{Official website}}

{{Apache Software Foundation}}

{{DEFAULTSORT:Apache Maven}}
[[Category:Compiling tools]]
[[Category:Java development tools]]
[[Category:Apache Software Foundation projects|Maven]]
[[Category:Build automation|Maven]]
[[Category:Software using the Apache license]]