Maven - A simplistic start to an AEM project

Apache Maven is an open-source project management and comprehension tool that automates builds and provides quality project information, and it’s the recommended build management tool for AEM projects.

Maven archetype for AEM project
It's not possible whenever you want to create a new AEM project; you manually create the folder, files and the whole project structure, that is where the maven archetypes come in picture. Maven archetypes provide us with predefined project structure templates for AEM.

With the help of maven archetypes, a developer can create a new project which will be in a way with the best industry practices and recommended by Adobe.

Maven archetypes also include a sample project, which helps developer to get introduced to best practices and features employed by maven.
Using an Archetype 10 or above project, you are given a set of files to start with.

Maven Setup:

• Download Maven(Binary zip file) from http://maven.apache.org/download.cgi
• Extract the zip file to your C directory
• Create new environment variables and enter values of java and maven path: 
• JAVA_HOME - C:\Program Files\Java\jdk1.8.0_31
• M3_HOME - C:\apache-maven-3.5.3-bin\apache-maven-3.5.
• Edit Path environment variable and add jdk bin path(if not already added) and maven bin path: %M3_HOME%\bin; %JAVA_HOME%\bin
• Test if Maven is properly configured by typing below command in command prompt (It should give you maven and java home and versions): mvn –version
• Create .m2 folder for maven repository: Go to C:\Users\(your user name), create .m2 folder and create a file settings.xml (you can copy the content of settings.xml from here ) in that folder.

Creating a Maven archetype 12 project
To create an AEM archetype (version 12) project, perform these steps:

• Open the command prompt and go to your project folder.
• Run the following Maven command:

mvn org.apache.maven.plugins:maven-archetype-plugin:2.4:generate -DarchetypeGroupId=com.adobe.granite.archetypes -DarchetypeArtifactId=aem-project-archetype -DarchetypeVersion=12 -DarchetypeCatalog=https://repo.adobe.com/nexus/content/groups/public/

• When prompted, specify the following information:

• Once done, you will see a message like:

• And your working directory is added with below project structure:

Add Maven project in Eclipse:

• Click on File-> Import -> Maven -> Existing Maven Projects
• Select the project from your drive, click Finish:

You can see below files and packages in Eclipse, and accordingly, you can add/modify files.

After you import the project into Eclipse, notice each module is a separate Eclipse project:

• core - where Java files that are used in OSGi services and sling servlets, sling models are located
• launcher - where additional Java files are located
• tests - Java files for tests like JUNIT tests
• apps - content under /apps
• content - content under /content

When you want to create an OSGi service, you work under the core. Likewise, if you want to create an HTL component, you can work under apps.

Code Deployment in AEM using maven:

• To build the OSGi bundle by using Maven, perform these steps:
• Open the command prompt and go to your project folder.
• Run the following maven command: mvn -PautoInstallPackage install.
• After the build success, the OSGi bundle can be found in the following folder: (you folder path)\MyProject\core\target. The name of the OSGi bundle is MyProject.core-1.0-SNAPSHOT.jar.

The above command automatically deploys the OSGi bundle and apps package to AEM.

• Make sure after you deploy code, your bundle is in active state, you can check it at http://localhost:4502/system/console/bundles

• Also, you can see the following components and items installed in your crxde along with a sample page inside content named MyProject.

Dependency Mechanism in Maven
Dependency management is one of the features of Maven that is best known to users and is one of the areas where Maven excels. There is not much difficulty in managing dependencies for a single a project, but when you start getting into dealing with multi-module projects and applications that consist of tens or hundreds of modules this is where Maven can help you a great deal in maintaining a high degree of control and stability.

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.
For ex: you can add the below dependency in the parent POM of the project like this:

<dependency>

    <groupId>com.adobe.aem</groupId>

    <artifactId>uber-jar</artifactId>

    <version>6.3.0</version>

    <classifier>apis</classifier>

    <scope>provided</scope>

</dependency>

And have its reference in the core POM.xml as below:

<dependency>

    <groupId>com.adobe.aem</groupId>

    <artifactId>uber-jar</artifactId>

    <classifier>apis</classifier>

</dependency>

The above JAR file (uber-jar) contains all of the public Java APIs exposed by Adobe Experience Manager. It includes limited external libraries as well, specifically all public APIs available in AEM. 

The minimal set of information for matching a dependency reference against a dependency Management section is actually {groupId, artifactId, type, classifier}. But we can shorthand the identity set to {groupId, artifactId}, since the default for the type field is the jar, and the default classifier is null.
So, now you are good to go!! Just create your project and start developing.

References: https://helpx.adobe.com/experience-manager/using/maven_arch12.html