Introduction

By default, !LessCss is not included in maven plugin. In order to use it as a build time solution you have a couple of solutions described below.

Use ConfigurableWroManagerFactory

The ConfigurableWroManagerFactory is a very useful implementation of !WroManagerFactory which allows user to easily configure processors to be used during maven execution.

Update the pom.xml with the following configuration:

<plugin>
    <groupId>ro.isdc.wro4j</groupId>
    <artifactId>wro4j-maven-plugin</artifactId>
    <version>${wro4j.version}</version>
    <configuration>
      <wroManagerFactory>ro.isdc.wro.maven.plugin.manager.factory.ConfigurableWroManagerFactory</wroManagerFactory>
    </configuration>
</plugin>       

When ConfigurableWroManagerFactory is used, wro4j will search for a configuration file located at /WEB-INF/wro.properties location (same as for runtime solution).

Update wro.properties and add lessCss processor:

#Use less css as preProcessor
preProcessors=lessCss
#Use less css as postProcessor
postProcessors=lessCss

You can also add other processors along with the lessCss processor separated by comma. Example:

#Use less css as preProcessor
preProcessors=cssImport,lessCss

The wro.properties also can contains additional configuration options. You can find more about them on [ConfigurationOptions Configuration Options] page.

Create custom a wro manager factory class

(extend DefaultStandaloneContextAwareManagerFactory, @see GoogleStandaloneManagerFactory as example) which add the !LessCss processor to the chain of existing processors

public class LessCssSupportStandaloneManagerFactory extends 
DefaultStandaloneContextAwareManagerFactory { 
    @Override
    protected ProcessorsFactory newProcessorsFactory() {         
      return new SimpleProcessorsFactory().addPostProcessor(new LessCssProcessor());  
    }
} 

This custom factory called LessCssSupportStandaloneManagerFactory, uses a processorFactory which configures lessCss as a post processor only. You can also add more processors and decide the order in which they are executed.

Update the maven configuration plugin in pom.xml

<plugin> 
  <groupId>ro.isdc.wro4j</groupId> 
  <artifactId>wro4j-maven-plugin</artifactId> 
  <version>${wro4j.version}</version> 
  <executions> 
    <execution> 
      <goals> 
        <goal>run</goal> 
      </goals> 
    </execution> 
  </executions> 
  <configuration> 
    <wroManagerFactory>com.mycompany.LessCssSupportStandaloneManagerFactory</wroManagerFactory> 
  </configuration> 
</plugin> 

This way you can instruct maven plugin what processors to use during the build time for compressing/processing resources.