Maven - Maven POM - maven tutorial
maven tutorial tags : apache maven , maven repository , maven central
What is POM in Maven ?
- POM stands for Project Object Model.
- It is fundamental Unit of Work in Maven.
- POM is an XML file.
- It always resides in the base directory of the project as pom.xml.
- The POM contains information about the project and various configuration detail used by Maven to build the project(s).
- POM also contains the goals and plugins.
- While executing a task or goal, Maven looks for the POM in the current directory.
- It reads the POM, gets the needed configuration information, then executes the goal.
- Some of the configuration that can be specified in the POM are following:
- project dependencies
- plugins
- goals
- build profiles
- project version
- developers
- mailing list
- Before creating a POM, we should first decide the project group (groupId), its name(artifactId) and its version as these attributes help in uniquely identifying the project in repository.
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Learn Maven Tutorial - Maven POM - Maven Example
Sample Code:
<project xmlns="http://maven.apache.org/POM/4.0.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.companyname.project-group</groupId>
<artifactId>project</artifactId>
<version>1.0</version>
</project>
- It should be noted that there should be a single POM file for each project.
- All POM files require the project element and three mandatory fields: groupId, artifactId,version.
- Projects notation in repository is groupId:artifactId:version.
- Root element of POM.xml is project and it has three major sub-nodes :
| Node | Description |
|---|---|
| groupId | This is an Id of project's group. This is generally unique amongst an organization or a project. For example, a banking group com.company.bank has all bank related projects. |
| artifactId | This is an Id of the project.This is generally name of the project. For example, consumer-banking. Along with the groupId, the artifactId defines the artifact's location within the repository. |
| version | This is the version of the project.Along with the groupId, It is used within an artifact's repository to separate versions from each other. For example:
com.company.bank:consumer-banking:1.0 com.company.bank:consumer-banking:1.1. |
Learn Maven Tutorial - Maven POM - Maven Example
Super POM
- All POMs inherit from a parent (despite explicitly defined or not).
- POM is known as the Super POM, and contains values inherited by default.
- Maven use the effective pom (configuration from super pom plus project configuration) to execute relevant goal.
- POM helps developer to specify minimum configuration detail in his/her pom.xml.
- Although configurations can be overridden easily.
- An easy way to look at the default configurations of the super POM is by running the following command: mvn help:effective-pom
- Create a pom.xml in any directory on your computer.Use the content of above mentioned example pom.
- In example below, We've created a pom.xml in C:\MVN\project folder.
- Now open command console, go the folder containing pom.xml and execute the following mvn command.
C:\MVN\project>mvn help:effective-pom
- Maven will start processing and display the effective-pom.
[INFO] Scanning for projects...
[INFO] Searching repository for plugin with prefix: 'help'.
[INFO] ------------------------------------------------------------------------
[INFO] Building Unnamed - com.companyname.project-group:project-name:jar:1.0
[INFO] task-segment: [help:effective-pom] (aggregator-style)
[INFO] ------------------------------------------------------------------------
[INFO] [help:effective-pom {execution: default-cli}]
[INFO]
.....
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
[INFO] Total time: < 1 second
[INFO] Finished at: Thu Jul 05 11:41:51 IST 2012
[INFO] Final Memory: 6M/15M
[INFO] ------------------------------------------------------------------------
- Effective POM displayed as result in console, after inheritance, interpolation, and profiles are applied.
maven tutorial tags : apache maven , maven repository , maven central
Sample Code
<!-- ====================================================================== -->
<!-- -->
<!-- Generated by Maven Help Plugin on 2015-09-26T07:51:19 -->
<!-- See: http://maven.apache.org/plugins/maven-help-plugin/ -->
<!-- -->
<!-- ====================================================================== -->
<!-- ====================================================================== -->
<!-- -->
<!-- Effective POM for project -->
<!-- 'com.companyname.project-group:project:jar:1.0' -->
<!-- -->
<!-- ====================================================================== -->
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/
2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 h
ttp://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.companyname.project-group</groupId>
<artifactId>project</artifactId>
<version>1.0</version>
<repositories>
<repository>
<snapshots>
<enabled>false</enabled>
</snapshots>
<id>central</id>
<name>Central Repository</name>
<url>https://repo.maven.apache.org/maven2</url>
</repository>
</repositories>
<pluginRepositories>
<pluginRepository>
<releases>
<updatePolicy>never</updatePolicy>
</releases>
<snapshots>
<enabled>false</enabled>
</snapshots>
<id>central</id>
<name>Central Repository</name>
<url>https://repo.maven.apache.org/maven2</url>
</pluginRepository>
</pluginRepositories>
<build>
<sourceDirectory>C:\MVN\project\src\main\java</sourceDirectory>
<scriptSourceDirectory>C:\MVN\project\src\main\scripts</scriptSourceDirector
y>
<testSourceDirectory>C:\MVN\project\src\test\java</testSourceDirectory>
<outputDirectory>C:\MVN\project\target\classes</outputDirectory>
<testOutputDirectory>C:\MVN\project\target\test-classes</testOutputDirectory
>
<resources>
<resource>
<directory>C:\MVN\project\src\main\resources</directory>
</resource>
</resources>
<testResources>
<testResource>
<directory>C:\MVN\project\src\test\resources</directory>
</testResource>
</testResources>
<directory>C:\MVN\project\target</directory>
<finalName>project-1.0</finalName>
<pluginManagement>
<plugins>
<plugin>
<artifactId>maven-antrun-plugin</artifactId>
<version>1.3</version>
</plugin>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.2-beta-5</version>
</plugin>
<plugin>
<artifactId>maven-dependency-plugin</artifactId>
<version>2.8</version>
</plugin>
<plugin>
<artifactId>maven-release-plugin</artifactId>
<version>2.3.2</version>
</plugin>
</plugins>
</pluginManagement>
<plugins>
<plugin>
<artifactId>maven-clean-plugin</artifactId>
<version>2.5</version>
<executions>
<execution>
<id>default-clean</id>
<phase>clean</phase>
<goals>
<goal>clean</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<artifactId>maven-install-plugin</artifactId>
<version>2.4</version>
<executions>
<execution>
<id>default-install</id>
<phase>install</phase>
<goals>
<goal>install</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<artifactId>maven-resources-plugin</artifactId>
<version>2.6</version>
<executions>
<execution>
<id>default-resources</id>
<phase>process-resources</phase>
<goals>
<goal>resources</goal>
</goals>
</execution>
<execution>
<id>default-testResources</id>
<phase>process-test-resources</phase>
<goals>
<goal>testResources</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.12.4</version>
<executions>
<execution>
<id>default-test</id>
<phase>test</phase>
<goals>
<goal>test</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.1</version>
<executions>
<execution>
<id>default-testCompile</id>
<phase>test-compile</phase>
<goals>
<goal>testCompile</goal>
</goals>
</execution>
<execution>
<id>default-compile</id>
<phase>compile</phase>
<goals>
<goal>compile</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<artifactId>maven-jar-plugin</artifactId>
<version>2.4</version>
<executions>
<execution>
<id>default-jar</id>
<phase>package</phase>
<goals>
<goal>jar</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<artifactId>maven-deploy-plugin</artifactId>
<version>2.7</version>
<executions>
<execution>
<id>default-deploy</id>
<phase>deploy</phase>
<goals>
<goal>deploy</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<artifactId>maven-site-plugin</artifactId>
<version>3.3</version>
<executions>
<execution>
<id>default-site</id>
<phase>site</phase>
<goals>
<goal>site</goal>
</goals>
<configuration>
<outputDirectory>C:\MVN\project\target\site</outputDirectory>
<reportPlugins>
<reportPlugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-project-info-reports-plugin</artifactId>
</reportPlugin>
</reportPlugins>
</configuration>
</execution>
<execution>
<id>default-deploy</id>
<phase>site-deploy</phase>
<goals>
<goal>deploy</goal>
</goals>
<configuration>
<outputDirectory>C:\MVN\project\target\site</outputDirectory>
<reportPlugins>
<reportPlugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-project-info-reports-plugin</artifactId>
</reportPlugin>
</reportPlugins>
</configuration>
</execution>
</executions>
<configuration>
<outputDirectory>C:\MVN\project\target\site</outputDirectory>
<reportPlugins>
<reportPlugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-project-info-reports-plugin</artifactId>
</reportPlugin>
</reportPlugins>
</configuration>
</plugin>
</plugins>
</build>
<reporting>
<outputDirectory>C:\MVN\project\target\site</outputDirectory>
</reporting>
</project>
POM important attributes :
learn maven tutorial - POM important attributes - maven example programs
POM Sample attributes :
learn maven tutorial - POM Sample attributes - maven example programs
- In above pom.xml , the default project source folders structure,output directory, plug-ins required, repositories, reporting directory are seen, which Maven will be using while executing the desired goals.
- Maven pom.xml is also not required to be written manually.
- Maven provides numerous archetype plugins to create projects which in order create the project structure and pom.xml