How to Create Maven Multi Module using Command Line


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Maven Tutorial



In this tutorial, we will learn how to create a simple Java multi-module Maven project using Command-Line with very easy steps. 

A multi-module project is defined by a parent POM referencing one or more sub-modules. 

Real-world examples of maven multi-module projects are :
1. https://github.com/RameshMF/junit-developer-guide
2. https://github.com/spring-projects/spring-framework
3. https://github.com/apache/maven
4. https://github.com/jersey/jersey

Create a Maven Multi-Module using Command Line

In this tutorial, we will create a blogger web application with different modules. 
Let's create a blogger as a parent project and its 3 sub-modules are:
-  blogger-core
- blogger-common
- blogger-web.
Below are the steps to create parent and sub-modules projects.

1 Create Parent project - blogger

Let's use the below command to create the parent Maven project:
mvn archetype:generate -DgroupId=com.companyname.blogger -DartifactId=blogger
Note that the whole command should be a single line. After build success, we will see the below output in the command line console.
[INFO] Parameter: package, Value: com.companyname.blogger
[INFO] Parameter: groupId, Value: com.companyname.blogger
[INFO] Parameter: artifactId, Value: blogger
[INFO] Parameter: packageName, Value: com.companyname.blogger
[INFO] Parameter: version, Value: 1.0-SNAPSHOT
[INFO] project created from Old (1.x) Archetype in dir: C:\Ramesh_Study\maven\guides\blogger
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 01:09 min
[INFO] Finished at: 2018-06-20T13:40:40+05:30
[INFO] ------------------------------------------------------------------------

2. Update pom.xml to declare it as a Parent project

Open pom.xml of the above-created Parent Maven project (blogger) and change the packaging to ‘pom’.
 <packaging>pom</packaging>
The complete pom.xml
<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.blogger</groupId>
  <artifactId>blogger</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>pom</packaging>
  <name>blogger</name>
  <url>http://maven.apache.org</url>

  <properties>
       <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
         <groupId>junit</groupId>
         <artifactId>junit</artifactId>
         <version>3.8.1</version>
         <scope>test</scope>
    </dependency>
  </dependencies>
</project>
If you don't change this pom.xml then you will get the below build fail error:
[INFO] Parameter: groupId, Value: com.companyname.blogger
[INFO] Parameter: artifactId, Value: blogger-core
[INFO] Parameter: version, Value: 1.0-SNAPSHOT
[INFO] Parameter: package, Value: com.companyname.blogger
[INFO] Parameter: packageInPathFormat, Value: com/companyname/blogger
[INFO] Parameter: version, Value: 1.0-SNAPSHOT
[INFO] Parameter: package, Value: com.companyname.blogger
[INFO] Parameter: groupId, Value: com.companyname.blogger
[INFO] Parameter: artifactId, Value: blogger-core
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 01:49 min
[INFO] Finished at: 2018-06-20T13:49:18+05:30
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-archetype-plugin:3.0.1:generate (default-cli) validPackaging: **Unable to add module to the current project as it is not of packaging type 'pom'** -> [Help 1]

3. Create Sub-modules

Change directory via below command
cd blogger
Let's create sub-modules in blogger parent project.
  1. Create blogger-core module.
mvn archetype:generate -DgroupId=com.companyname.blogger  -DartifactId=blogger-core
  1. Create blogger-common module
mvn archetype:generate -DgroupId=com.companyname.blogger  -DartifactId=blogger-common
  1. Create blogger-web module and it is a web application packaged with a war file. The archetype for maven web application is -DarchetypeArtifactId=maven-archetype-webapp
mvn archetype:generate -DgroupId=com.companyname.blogger  -DartifactId=blogger-web -DarchetypeArtifactId=maven-archetype-webapp
Now if you open the blogger parent project pom.xml, you will find all three modules being added in there.
 <modules>
    <module>blogger-core</module>
    <module>blogger-common</module>
    <module>blogger-web</module>
  </modules>
Also, in each sub-module  pom.xml, a parent section is being added.
 <parent>
    <artifactId>blogger</artifactId>
    <groupId>com.companyname.blogger</groupId>
    <version>1.0-SNAPSHOT</version>
  </parent>

4. Update Sub-Modules pom.xml

Open pom.xml of the blogger-core module and update the packaging with jar:
<packaging>jar</packaging>
Open pom.xml of the blogger-common module and update the packaging with jar:
<packaging>jar</packaging>
Open pom.xml of the blogger-web module and update the packaging with war:
<packaging>war</packaging>
Let's see complete updated pom.xml files for all the parent and sub-modules.

1. blogger parent project pom.xml:
<?xml version="1.0" encoding="UTF-8"?>
<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.blogger</groupId>
  <artifactId>blogger</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>pom</packaging>

  <name>blogger</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
  <modules>
    <module>blogger-common</module>
    <module>blogger-web</module>
    <module>blogger-core</module>
  </modules>
</project>
2. blogger-core sub-module pom.xml:
<?xml version="1.0" encoding="UTF-8"?>
<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>
  <parent>
    <artifactId>blogger</artifactId>
    <groupId>com.companyname.blogger</groupId>
    <version>1.0-SNAPSHOT</version>
  </parent>

  <groupId>com.companyname.blogger</groupId>
  <artifactId>blogger-core</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>jar</packaging>
  <name>blogger-core</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.7</maven.compiler.source>
    <maven.compiler.target>1.7</maven.compiler.target>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
</project>
3. blogger-common sub-module pom.xml:
<?xml version="1.0" encoding="UTF-8"?>
<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>
  <parent>
    <artifactId>blogger</artifactId>
    <groupId>com.companyname.blogger</groupId>
    <version>1.0-SNAPSHOT</version>
  </parent>

  <groupId>com.companyname.blogger</groupId>
  <artifactId>blogger-common</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>jar</packaging>
  <name>blogger-common</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.7</maven.compiler.source>
    <maven.compiler.target>1.7</maven.compiler.target>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
</project>
4. blogger-web sub-module pom.xml:
<?xml version="1.0"?>
<project xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd" xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <modelVersion>4.0.0</modelVersion>
  <parent>
    <groupId>com.companyname.blogger</groupId>
    <artifactId>blogger</artifactId>
    <version>1.0-SNAPSHOT</version>
  </parent>
  <groupId>com.companyname.blogger</groupId>
  <artifactId>blogger-web</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>war</packaging>
  <name>blogger-web Maven Webapp</name>
  <url>http://maven.apache.org</url>
  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
  </dependencies>
  <build>
    <finalName>blogger-web</finalName>
  </build>
</project>

5. Build Multi-Module

To test all the multi-module project setup is correct then run below maven common on blogger parent project:
mvn clean install
The output of the above command
[INFO] Reactor Summary:
[INFO]
[INFO] blogger 1.0-SNAPSHOT ............................... SUCCESS [  0.746 s]
[INFO] blogger-common ..................................... SUCCESS [  5.727 s]
[INFO] blogger-core ....................................... SUCCESS [  1.775 s]
[INFO] blogger-web Maven Webapp 1.0-SNAPSHOT .............. SUCCESS [  0.809 s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 9.289 s
[INFO] Finished at: 2018-06-20T14:20:05+05:30
[INFO] ------------------------------------------------------------------------
That's it. 
Now can import this project into Eclipse IDE. In Eclipse , File->Import->Maven->Existing Maven projects

Conclusion

In this tutorial, we have learned how to create a maven Multi-Module using Command Line by taking the blogger project as an example.

The source code of this multi-module project is available on GitHub.
Github Repository: Maven Multi Module Project.

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