Creating custom archetypes in Maven

As developers we embrace concepts like DRY (Don’t Re-invent Yourself). When we are creating similar things repetitively, we always prepare a template for that thing, so instead of starting a project from scratch, you can have a preconfigured directory structure. And in those directories you can place your template source files. Eg: struts.xml, spring config file, web.xml, tiles.xml etc..

Creating your archetype

Run the following command:

mvn archetype:generate \
-DgroupId=[your project's group id] \
-DartifactId=[your project's artifact id] \
-DarchetypeArtifactId=maven-archetype-archetype

This will create following default directory structure for creating archetypes.

archetype
|-- pom.xml
`-- src
    `-- main
        `-- resources
            |-- META-INF
            |   `-- maven
            |       `--archetype.xml
            `-- archetype-resources
                |-- pom.xml
                `-- src
                    |-- main
                    |   `-- java
                    |       `-- App.java
                    `-- test
                        `-- java
                            `-- AppTest.java

Think of maven-archetype-archetype as the maven’s template to create templates.

The generated archetype-descriptor is old and needs to be changed to use new features. To that end, rename the file archetype.xml to archetype-metadata.xml

Over write the following content to the file:

<archetype-descriptor xmlns="http://maven.apache.org/plugins/maven-archetype-plugin/archetype-descriptor/1.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://maven.apache.org/plugins/maven-archetype-plugin/archetype-descriptor/1.0.0 http://maven.apache.org/xsd/archetype-descriptor-1.0.0.xsd"
   name="simple-web"> <!-- name must be same as the project archetypeId -->
         <fileSets>
         <fileSet filtered="true" encoding="UTF-8">
             <directory>src/main/web</directory>
         </fileSet>
         <fileSet filtered="true" encoding="UTF-8">
             <directory>src/main/resources</directory>
         </fileSet>
         <fileSet filtered="true" encoding="UTF-8">
             <directory>src/test/resources</directory>
         </fileSet>
         <fileSet filtered="true" packaged="false">
             <directory>src/main/java</directory>
             <includes>
                 <include>**/*.java</include>
             </includes>
         </fileSet>
         <fileSet filtered="true">
             <directory>src/test/java</directory>
             <includes>
                 <include>**/*.java</include>
             </includes>
         </fileSet>
     </fileSets>
 </archetype-descriptor>

The above maven archetype descriptor file tells maven to copy (or create if not exists) any source files reside in web, src/main/java and corresponding test source directories. The archetype-resources directory is where all your template code should go. When you finally copy all your template files run the following command in maven to install your newly created artefact.

mvn install

You might want to continuously improve your template over time. Your artefact get installed multiple times during the process, so wrong versions of archetype may be installed. To counter that you might want to clean archetype cache by issuing following command:

mvn clean install -U

-U means force update of dependencies.

So whenever you want to create a new project using your archetype run following command:

mvn archetype:generate -DarchetypeGroupId=com.my-template
 -DarchetypeArtifactId=template-name -DarchetypeVersion=1.0
 -DgroupId=proj.groupid -DartifactId=projectid

So there you have it! This single line command can load all your template source files and create whole directory structure of your application.