Q:

How to fix "Error: JavaFX runtime components are missing, and are required to run this application"

My JavaFx application is running perfectly well from source but When I'm compiling to a single jar file I get error : 

Error: JavaFX runtime components are missing, and are required to run this application.

I'm using Maven as my repository manager and My install with Maven is sucessfull. 
Note: In my Intellij build artifact I can see that Intellij include JavaFx and all its libraries

A:

a) For my maven project the trick was to use an extra starter class that does not inherit from javafx.application.Application:
public class GUIStarter {

    public static void main(final String[] args) {
        GUI.main(args);
    }

}

The JavaFx dependencies are included in my pom.xml as follows:
<!-- JavaFx -->
        <dependency>
            <groupId>org.openjfx</groupId>
            <artifactId>javafx-base</artifactId>
            <version>12</version>
        </dependency>

        <dependency>
            <groupId>org.openjfx</groupId>
            <artifactId>javafx-controls</artifactId>
            <version>12</version>
        </dependency>

        <dependency>
            <groupId>org.openjfx</groupId>
            <artifactId>javafx-graphics </artifactId>
            <version>12</version>
            <classifier>win</classifier>
        </dependency>

        <dependency>
            <groupId>org.openjfx</groupId>
            <artifactId>javafx-fxml</artifactId>
            <version>12</version>
        </dependency>

        <dependency>
            <groupId>org.openjfx</groupId>
            <artifactId>javafx-web</artifactId>
            <version>12</version>
        </dependency>

        <dependency>
            <groupId>org.openjfx</groupId>
            <artifactId>javafx-media</artifactId>
            <version>12</version>
        </dependency>

         <dependency>
            <groupId>org.openjfx</groupId>
            <artifactId>javafx-swing</artifactId>
            <version>12</version>
        </dependency>

In order to include fxml files in your build, you might need to define them as resource:
!-- define JavaFx files as resources to include them in the jar -->
<resource>
      <directory>${basedir}/src/main/java/foo/baa/view</directory>
      <filtering>false</filtering>  
      <targetPath>foo/baa/view</targetPath>            
</resource>

b) As an alternative, an extra maven plugin "javafx-maven-plugin" could be used to build the javafx appication, see example project at https://openjfx.io/openjfx-docs/#maven (This did not work for me. I have several pom files and want to reference the javafx dependencies in a sub project. My main class could not be found by the javafx-maven-plugin.)

