Do you ever sometime find a project that needs to be broken into modules? Yeah, that’s the S in SOLID, i.e., Single Responsibility Principle. Fear not, there’s Maven for that. Keep in mind, there are also other build tools than Maven that provides multi-module functionality. For this, I’ll choose to use Maven because it’s easy for a small project. For a larger project, I’d recommend using Gradle.

To get started, you could follow the steps to create multi-module project.

  1. Let’s use Maven archetype and navigate into that folder: mvn archetype:generate -DgroupId=com.jmsweb -DartifactId=multi-module -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false; cd multi-module.
  2. Open multi-module/pom.xml and edit the file to add <packaging>pom</packaging> after <url>...</url>. This will become the parent POM for modules to build under.
  3. Once inside multi-module directory, run the archetype command one more time to generate a JAR module: mvn archetype:generate -DgroupId=com.jmsweb -DartifactId=child-module -DarchetypeArtifactId=maven-archetype-quickstart -DinteractiveMode=false; cd child-module.
  4. Open child-module/pom.xml and edit the file to add <packaging>jar</packaging> after <url>...</url>. This will become java JAR module to to build.
  5. The parent and child modules need to know about each other. Let’s open the child-module/pom.xml and add the following snippet:
     <parent>
     <groupId>com.jmsweb</groupId>
     <artifactId>multi-module</artifactId>
     <version>0.0.1-SNAPSHOT</version>
 </parent>
  6. The parent module need to know about its child modules. Let’s open the multi-module/pom.xml and add the following snippet:
     <modules>
     <module>child-module</module>
 </modules>
  7. If done correctly, you should be able to execute the command: mvn clean install in the multi-module directory. Maven will build the project and assemle the code into a nice JAR file under child-module/target/child-module.jar.

I’ve done this so many times that I can literally do this in my sleep, from command line, or from IDE. My apologizes if I did not provide enough steps. You can always get more information from Apache Maven Project website.