[FIXED] Java 11, JavaFX, Gradle, Eclipse, nasty failure message

Issue

OS: Linux Mint 18.3, Eclipse "2019-06". Gradle wrapper using Gradle 5.4.

Yesterday I spent about 4 hours trying to put together a project in Eclipse which would actually run and display a JavaFX Scene when using Java 11. I managed it in the end due to help from href="https://stackoverflow.com/a/52156678/595305">here.

But this was just a bog-standard "Java project" in Eclipse. What I actually need to do is develop a Gradle project, using Groovy as the main language.

Again, from the same gentleman, José Pereda, I found this answer. This does a Gradle "build" OK with the test below. But I get a nasty message when I use the Gradle "application" plugin's task "run": "Error: JavaFX runtime components are missing, and are required to run this application". I get this whether I run from inside Eclipse or from a Terminal.

So this is my build.gradle:

plugins {
     id 'java-library'
     id 'groovy'
     id 'eclipse'
     id 'application'
     id 'java'
}
mainClassName = 'core.App'
group 'Project'
version '1.0'
sourceCompatibility = 1.11
repositories {
     mavenCentral()
}
def currentOS = org.gradle.internal.os.OperatingSystem.current()
def platform
if (currentOS.isWindows()) {
     platform = 'win'
} else if (currentOS.isLinux()) {
     platform = 'linux'
} else if (currentOS.isMacOsX()) {
     platform = 'mac'
}
dependencies {
     api 'org.apache.commons:commons-math3:3.6.1'
     implementation 'com.google.guava:guava:27.0.1-jre'
     testImplementation 'junit:junit:4.12'
     implementation 'org.codehaus.groovy:groovy-all:2.5.8'
     testImplementation 'org.spockframework:spock-core:1.2-groovy-2.5'
     // these seemed to do the trick for a simple "Java project"
     // ... but Gradle seems to want something else (?)
     implementation "org.openjfx:javafx-base:11:${platform}"
     implementation "org.openjfx:javafx-graphics:11:${platform}"
     implementation "org.openjfx:javafx-controls:11:${platform}"
     implementation "org.openjfx:javafx-fxml:11:${platform}"
}

This is my application code:

import javafx.application.Application
import javafx.stage.Stage

class App extends Application {
    @Override
    public void start(Stage primaryStage) throws Exception {
        println "start...."
    }

    public static void main(String[] args) {
        println "about to launch..."
        launch(args);
        println "...launched"
    }
}

and this is my test:

class FuncSpec extends Specification {
    def "JavaFX should run OK"(){
        when:
        App app = new App()

        then:
        true
    }
}

Full output in Terminal after Gradle "run" is like so:

mike@M17A ~/software projects/eclipse-workspace/GrVocabSearch2019-09 $  ./gradlew run

> Task :run FAILED
Error: JavaFX runtime components are missing, and are required to run this application

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':run'.
> Process 'command '/usr/lib/jvm/java-11-openjdk-amd64/bin/java'' finished with non-zero exit value 1

Later

Followed José Pereda's indications to the letter in my build.gradle. This is what I get on trying to do a "run" task:

> Task :run FAILED
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.codehaus.groovy.vmplugin.v7.Java7$1 (file:/media/chris/W10%20D%20drive/apps/Chris.gradle/caches/modules-2/files-2.1/org.codehaus.groovy/groovy/2.5.8/2f1e8ea55e625fe51e85ef35eb067f1d9c61772d/groovy-2.5.8.jar) to constructor java.lang.invoke.MethodHandles$Lookup(java.lang.Class,int)
WARNING: Please consider reporting this to the maintainers of org.codehaus.groovy.vmplugin.v7.Java7$1
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release

java.lang.reflect.InvocationTargetException
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:566)
        at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:464)
        at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:363)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:566)
        at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1051)
Caused by: java.lang.RuntimeException: Error: class jdk.internal.reflect.NativeMethodAccessorImpl is not a subclass of javafx.application.Application
        at javafx.graphics/javafx.application.Application.launch(Application.java:298)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:566)
        at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:101)
        at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:323)
        at groovy.lang.MetaClassImpl.invokeStaticMethod(MetaClassImpl.java:1491)
        at org.codehaus.groovy.runtime.callsite.StaticMetaClassSite.callStatic(StaticMetaClassSite.java:62)
        at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCallStatic(CallSiteArray.java:55)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callStatic(AbstractCallSite.java:196)
        at org.codehaus.groovy.runtime.callsite.AbstractCallSite.callStatic(AbstractCallSite.java:208)
        at core.App.main(main.groovy:60)
        ... 11 more
Exception running application core.App

FAILURE: Build failed with an exception

Note

I believe this is not a duplicate of any answer which does not mention Gradle. I have got this working in a normal Java run.

Solution

The reason for the issue:

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

has been answered a number of times already (including with Gradle), but since you are still using the "old" approach to include the JavaFX dependencies, instead of using the JavaFX plugin, I'll explain how to fix this.

Error

If you check the JavaFX documentation for Eclipse, section IDE (either modular or non-modular projects), there is a clear explanation of this issue:

Or, in other words, JavaFX dependencies are modular and have to be added to the module-path.

First Solution

If you keep reading, you will find immediately an explanation on how to fix it (providing you are not using build tools):

However, since you are using Gradle, the solution has to be adapted to be included in your build file.

This is the way it was done, before using the JavaFX plugin:

compileJava {
    doFirst {
        options.compilerArgs = [
                '--module-path', classpath.asPath,
                '--add-modules', 'javafx.controls,javafx.fxml'
        ]
    }
}

run {
    doFirst {
        jvmArgs = [
                '--module-path', classpath.asPath,
                '--add-modules', 'javafx.controls,javafx.fxml'
        ]
    }
}

Now you should be able to run:

./gradlew run

By the way, you can still see here the build of a HelloFX sample referred from the documentation, before using the plugin.

JavaFX plugin

The JavaFX plugin for Gradle was created precisely to deal with all the "boilerplate code" in the build file.

If you check now the documentation for Eclipse, sections Gradle (modular or non modular), or the same updated sample you will see that the build file is simplified to this:

plugins {
  id 'application'
  id 'org.openjfx.javafxplugin' version '0.0.8'
}

repositories {
    mavenCentral()
}

dependencies {
}

javafx {
    version = "13"
    modules = [ 'javafx.controls', 'javafx.fxml' ]
}

mainClassName = 'org.openjfx.MainApp'

In your case, you just need to adapt this to your build file, something like:

plugins {
    id 'java-library'
    id 'groovy'
    id 'eclipse'
    id 'application'
    id 'org.openjfx.javafxplugin' version '0.0.8'
}

mainClassName = 'core.App'
group 'Project'
version '1.0'
sourceCompatibility = 11

repositories {
    mavenCentral()
}

dependencies {
    api 'org.apache.commons:commons-math3:3.6.1'
    implementation 'com.google.guava:guava:27.0.1-jre'
    testImplementation 'junit:junit:4.12'
    implementation 'org.codehaus.groovy:groovy-all:2.5.8'
    testImplementation 'org.spockframework:spock-core:1.2-groovy-2.5'
}

javafx {
    version = "13"
    modules = [ "javafx.controls", "javafx.fxml" ]
}

and run:

./gradlew run

Answered By - José Pereda
Answer Checked By - Robin (JavaFixing Admin)