Maven Guide

Maven Lifecycle Goals

1. mvn compile : This will run Maven, telling it to execute the compile goal. When it’s finished, you should find the compiled .class files in the target/classes directory.
2. mvn package : The package goal will compile your Java code, run any tests, and finish by packaging the code up in a JAR file within the target directory. The name of the JAR file will be based on the project’s <artifactId> and <version>. For example, given the minimal pom.xml file from before, the JAR file will be named gs-maven-0.1.0.jar.
3. mvn install : The install goal will compile, test, and package your project’s code and then copy it into the local dependency repository, ready for another project to reference it as a dependency.
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Questions :

1. What is the parent section in a pom.xml ? 

2. The Scenario

   As an example, let us reuse our previous artifact, com.mycompany.app:my-app:1. And let us introduce another artifact, com.mycompany.app:my-module:1.

   <project>
     <modelVersion>4.0.0</modelVersion>
     <groupId>com.mycompany.app</groupId>
     <artifactId>my-module</artifactId>
     <version>1</version>
   </project>

   And let us specify their directory structure as the following:

   .
    |-- my-module
    |   `-- pom.xml
    `-- pom.xml

   Note: my-module/pom.xml is the POM of com.mycompany.app:my-module:1 while pom.xml is the POM of com.mycompany.app:my-app:1

   The Solution

   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:

   com.mycompany.app:my-module:1's POM

   <project>
     <parent>
       <groupId>com.mycompany.app</groupId>
       <artifactId>my-app</artifactId>
       <version>1</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
     <groupId>com.mycompany.app</groupId>
     <artifactId>my-module</artifactId>
     <version>1</version>
   </project>

   Notice that we now have an added section, the parent section. This section allows us to specify which artifact is the parent of our POM. And we do so by specifying the fully qualified artifact name of the parent POM. With this setup, our module can now inherit some of the properties of our parent POM.

   Alternatively, if we want the groupId and / or the version of your modules to be the same as their parents, you can remove the groupId and / or the version identity of your module in its POM.

   <project>
     <parent>
       <groupId>com.mycompany.app</groupId>
       <artifactId>my-app</artifactId>
       <version>1</version>
     </parent>
     <modelVersion>4.0.0</modelVersion>
     <artifactId>my-module</artifactId>
   </project>

   This allows the module to inherit the groupId and / or the version of its parent POM.
    
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References :

1. http://stackoverflow.com/questions/2200725/questions-to-determine-maven-knowledge
2. http://spring.io/guides/gs/maven/
3. http://maven.apache.org/guides/ 
4.  http://maven.apache.org/guides/introduction/introduction-to-the-pom.html
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