How can I provide custom logic in a Maven archetype?

Question

I\'m interested in creating a Maven archetype, and I think I have most of the basics down. However, one thing I\'m stuck on is that sometimes I want to use custom logic to fill

Answer 1

The required properties section of the archetype-metatadata xml is used to pass additional properties to the velocity context, it is not meant for passing velocity engine configuration. So setting a property called userDirective will only make the variable $userDirective availble and not add a custom directive to the velocity engine.

If you see the source code, the velocity engine used by maven-archetype plugin does not depend on any external property source for its configuration. The code that generates the project relies on an autowired (by the plexus container) implementation of VelocityComponent.

This is the code where the velocity engine is initialized:

public void initialize()
    throws InitializationException
{
    engine = new VelocityEngine();

    // avoid "unable to find resource 'VM_global_library.vm' in any resource loader."
    engine.setProperty( "velocimacro.library", "" );

    engine.setProperty( RuntimeConstants.RUNTIME_LOG_LOGSYSTEM, this );

    if ( properties != null )
    {
        for ( Enumeration e = properties.propertyNames(); e.hasMoreElements(); )
        {
            String key = e.nextElement().toString();

            String value = properties.getProperty( key );

            engine.setProperty( key, value );

            getLogger().debug( "Setting property: " + key + " => '" + value + "'." );
        }
    }

    try
    {
        engine.init();
    }
    catch ( Exception e )
    {
        throw new InitializationException( "Cannot start the velocity engine: ", e );
    }
}

There is a hacky way of adding your custom directive. The properties you see above are read from the components.xml file in the plexus-velocity-1.1.8.jar. So open this file and add your configuration property

  
    
      org.codehaus.plexus.velocity.VelocityComponent
      default
      org.codehaus.plexus.velocity.DefaultVelocityComponent
      
        
          
            resource.loader
            classpath,site
          
          ...
          
            userdirective
            com.jlarge.HyphenatedToCamelCaseDirective
          
        
      
    
  

Next add your custom directive class file to this jar and run archetype:generate.

As you see this is very fraglie and you will need to figure a way to distribute this hacked plexus-velocity jar. Depending on what you are planning to use this archetype for it might be worth the effort.