How to run JavaFX application using JDK 11/Maven/Eclipse IDE

Question

The problem: Running a JavaFX application that is based on a Maven non-module project (project name = “howdyjfx”) from the Eclipse IDE generates the following compilation error:

[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.6.0:java (default-cli) on project howdyjfx: The parameters 'mainClass' for goal org.codehaus.mojo:exec-maven-plugin:1.6.0:java are missing or invalid.

Development environment and configuration:

• OS: Windows 10
• IDE: Eclipse 2019-03 (4.11.0)
• Installed JDK: jdk-11.0.3, this is the default (and only) JDK installed in the workspace. The project build path is Java SE-11 (jdk-11.0.3). Because Eclipse requires a Java 1.8 JRE, jdk1.8.0_211 is also installed on my computer; Eclipse will not run without this.
• Builder: All projects are non-modular and compiled using Maven. Eclipse handles this with its built-in m2e feature.
• Pom: Here's an extract from the pom:

    <modelVersion>4.0.0</modelVersion>
    <groupId>com.spindotta.jfx11.testbed</groupId>
    <artifactId>howdyjfx</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.openjfx/javafx-controls -->
        <dependency>
            <groupId>org.openjfx</groupId>
            <artifactId>javafx-controls</artifactId>
            <version>13-ea+8</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.openjfx/javafx-fxml -->
        <dependency>
            <groupId>org.openjfx</groupId>
            <artifactId>javafx-fxml</artifactId>
            <version>13-ea+8</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <!-- http://maven.apache.org/plugins/maven-compiler-plugin/ -->
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.0</version>
                <configuration>
                    <source>11</source>
                    <target>11</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-source-plugin</artifactId>
                <version>3.0.1</version>
                <executions>
                    <execution>
                        <id>attach-sources</id>
                        <goals>
                            <goal>jar</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.openjfx</groupId>
                <artifactId>javafx-maven-plugin</artifactId>
                <version>0.0.2</version>

                <configuration>
                    <!-- Is this necessary? The 'Run' configuration goals are "clean exec:java" -->
                    <executable>C:\Program Files\Java\jdk-11.0.3\bin\java</executable>

                    <!-- Workaround to short-circuit jdk1.8 which is needed to run Eclipse 
                        but is toxic for jdk11 and higher -->
                    <options>
                        <option>-Djava.library.path=C:\tmp</option>
                    </options>

                    <!-- Main class - is this correct? -->
                    <mainClass>com.spindotta.jfx11.testbed.howdyjfx.HowdyJFX</mainClass>
                </configuration>
            </plugin>
        </plugins>
    </build>

The application code is:

    public class HowdyJFX extends Application {

         @Override
         public void start(Stage primaryStage) throws Exception {
              final String javaVersion = System.getProperty("java.version");
              final String javafxVersion = System.getProperty("javafx.version");
              final Label l = new Label("Hello, JavaFX " + javafxVersion + ", running on Java " + javaVersion + ".");
              final Scene scene = new Scene(new StackPane(l), 640, 480);
              primaryStage.setScene(scene);
              primaryStage.show();
          }

         public static void main(String[] args) {
             launch();
         }
    }

The above configuration and code is based on the 'Getting Started' guide and Sr. Jose Pereda's Github post, and also on the answer to a similar question that was asked last September. For whatever reason, however, I can't get this to work. This is all the more frustrating because I'm finishing an extensive library of JFX controls that compile without any problems (using both JDK 11 and JavaFX 11) and work fine in Scene Builder (apart from some Scene Builder issues that aren't relevant here).

Thanks in advance for any useful suggestions!

Answer 1

The configuration in the pom file is correct, but the specification for the main class in the <configuration> section of the javafx-maven-plugin is wrong. In the both the ‘Getting started’ guide and the material on the Github repo, the name for the mainClass is ‘ org.openjfx.hellofx.App, which is a combination of the <groupId> plus <artifactId> plus the simple class name. Because the <groupId> and <artifactId> for my project are com.spindotta.jfx11.testbed and howdyjfx, respectively, I combined them with the simple class name HowdyJFX. This was incorrect because the project has the standard Maven configuration source/main/java plus a top-level folder howdyjfx. Specifying howdyjfx/HowdyJFX as the mainClass in the plugin fixed the problem.

For what it’s worth, the items specified in the <configuration> for the javafx-maven-plugin are essential; omitting any will generate an ERROR. It should be possible to specify these values in the Run configurations -> JRE tab -> VM arguments, although I find it easier to handle this in the pom using a template.

Thanks to Jose Pereda for clarifying an issue with the Goals that must be specified in the Run configurations for the launch.

Now there is another problem. I need to be able to debug JavaFX applications that are launched by the method suggested in the Getting Started guide and the Github repo. I set an Eclipse breakpoint in the main class HowdyJFX at the first line where a variable is assigned, so that the application would stop at that point, which did not happen. Instead the application ran as if the breakpoint wasn’t there. This is a different issue than the one at hand and is raised elsewhere.