Automatic update of generated css files via m2e - eclipse

Question

I'm using the lesscss-maven-plugin to generate different css files to the target directory (target\generated-sources) and then use maven-war-plugin to add this directory as an webResouce. Those files will generate perfectly fine.
However the m2e-plugin (version 1.0.0) won't copy those files in the according web-resources folder (m2e-wtp\web-resources), when they have changed. Only when I run a eclipse "maven/update project" changes will be updated. But I want the changes to take affect automatically, when the files have changed. Here is my pom configuration:
<plugin>
<groupId>org.eclipse.m2e</groupId>
<artifactId>lifecycle-mapping</artifactId>
<version>1.0.0</version>
<configuration>
<lifecycleMappingMetadata>
<pluginExecutions><pluginExecution>
<pluginExecutionFilter>
<groupId>org.lesscss</groupId>
<artifactId>lesscss-maven-plugin</artifactId>
<versionRange>[1.3.3]</versionRange>
<goals>
<goal>compile</goal>
</goals>
</pluginExecutionFilter>
<action>
<execute>
<runOnIncremental>true</runOnIncremental>
<runOnConfiguration>true</runOnConfiguration>
</execute>
</action>
</pluginExecution>
</pluginExecutions>
</lifecycleMappingMetadata>
</configuration>
....
<plugin>
<groupId>org.lesscss</groupId>
<artifactId>lesscss-maven-plugin</artifactId>
<version>1.3.3</version>
<configuration>
<sourceDirectory>${project.basedir}/src/main/less</sourceDirectory>
<outputDirectory>${project.build.directory}/generated-sources/styles</outputDirectory>
<lessJs>${project.basedir}/tools/less/less-1.7.0.min.js</lessJs>
<includes>
<include>backend/backend-main.less</include>
<include>frontend/frontend-main.less</include>
</includes>
</configuration>
<executions>
<execution>
<phase>process-resources</phase>
<goals>
<goal>compile</goal>
</goals>
</execution>
</executions>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-war-plugin</artifactId>
<version>2.4</version>
<configuration>
<webResources>
<resource>
<directory>${project.build.directory}/generated-sources/styles</directory>
<targetPath>styles</targetPath>
</resource>
</webResources>
</configuration>
</plugin>

Answer 1

There are two options:
Use an m2e specific profile
This is similar to the workaround you found, but a bit cleaner as it activates the profile only on m2e and you use a property to set an alternative value for when you package not using m2e.
You create an m2e specific profile that, when activated, will put the files directly in the m2e-wtp/web-resources/styles directory
<properties>
<lesscss.outputDirectory>${project.build.directory}/${project.build.finalName}/styles</lesscss.outputDirectory>
</properties>
<profiles>
<profile>
<id>m2e</id>
<activation>
<property>
<name>m2e.version</name>
</property>
</activation>
<properties>
<lesscss.outputDirectory>${project.build.directory}/m2e-wtp/web-resources/styles</lesscss.outputDirectory>
</properties>
</profile>
</profiles>
<plugin>
<groupId>org.lesscss</groupId>
<artifactId>lesscss-maven-plugin</artifactId>
<version>1.3.3</version>
<configuration>
<sourceDirectory>${project.basedir}/src/main/webapp/styles</sourceDirectory>
<outputDirectory>${lesscss.outputDirectory}</outputDirectory>
</configuration>
<executions>
<execution>
<goals>
<goal>compile</goal>
</goals>
<phase>process-sources</phase>
</execution>
</executions>
</plugin>
Source: https://github.com/marceloverdijk/lesscss-maven-plugin/issues/8
Use m2e-wro4j
It promises to:
execute wro4j-maven-plugin:run on Eclipse incremental builds, if a change is detected on css, js, less, json, sass resources under wro4j-maven-plugin's contextFolder (src/main/webapp by default)
Source: https://github.com/jbosstools/m2e-wro4j

Answer 2

The idea for my actual workaround was to modify the css file in target\m2e-wtp by "hand".
(First I tried to copy the css files from target\generated-sources to target\m2e-wtp with the maven-resource-plugin, but for a unkown reason, even the maven-resource-plugin was not coping when the filed css files in target\generated-sources gets updated.)
So I came up with this soution: let the lesscss-maven-plugin generate the files twice, one bunch to target\generated-sources and the second one to target\m2e-wtp. Of course the lesscss-maven-plugin has only one output folder, so one has to run the less:compile goal twice. (This is a bit slow, but it works.)
Because one need the second bunch of css files only in eclipse I have added the second execution to an profile.
<profile>
<id>less-eclipse-m2e-workarround</id>
<!--
problem: Eclipse is not updating m2e-wtp folder when css files in generated-sources get modified
workarround: generate the css twice: the normal nonce for generated-sources and a second bunch (only
for eclipse) directly into m2e-wtp folder
to enable this profile add the profile-id to: project/properties/maven/active maven profiles
details: http://stackoverflow.com/questions/23521410/automatic-update-of-generated-css-files-via-m2e
-->
<build>
<plugins>
<plugin>
<groupId>org.lesscss</groupId>
<artifactId>lesscss-maven-plugin</artifactId>
<executions>
<execution>
<id>for-eclipse</id>
<phase>generate-resources</phase>
<goals>
<goal>compile</goal>
</goals>
<configuration>
<outputDirectory>${project.build.directory}/m2e-wtp/web-resources/styles</outputDirectory>
</configuration>
</execution>
</executions>
</plugin>
</plugins>
</build>
</profile>