Why would Gradle attempt to use Java 8 when I told it to run Java 14?

Question

I'm learning how to use Gradle to build projects in IntelliJ. I want to build a project involving OpenJFX. However, I encounter this error.

java.lang.UnsupportedClassVersionError: org/openjfx/gradle/JavaFXPlugin has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0
> org/openjfx/gradle/JavaFXPlugin has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0

From what I can figure out, Gradle is using Java 8 to run a Java 11 plugin. However, I put this in gradle.properties:

org.gradle.java.home=/C:/Users/<my user>/.jdks/openjdk-14.0.1

The reason it's in .jdks is because IntelliJ downloaded it earlier. The thing is, I told Gradle to use Java 14, yet it gives me an error as if it's being run by Java 8. What's wrong here?

Answer 1

I found out how to change Gradle's JVM. In IntelliJ, go to Preferences (Ctrl-Alt-S); then Build, Execution, Deployment; then Build Tools > Gradle. There's a little menu that lets you choose between the JVMs it recognizes.

Answer 2

According to the docs org.gradle.java.home property…

…specifies the Java home for the Gradle build process. The value can be set to either a jdk or jre location, however, depending on what your build does, using a JDK is safer. A reasonable default is derived from your environment (JAVA_HOME or the path to java) if the setting is unspecified. This does not affect the version of Java used to launch the Gradle client VM

So, this value is only used for build process (like compiling or running app or tests). Gradle spins up a child process for that, so the VM that performs tasks and the VM that runs the build script may not be the same.

It looks like you're using a Gradle plugin compiled with Java 11 (55.0), but your Gradle VM is Java 8 (52.0), so it cannot load and use plugin's class. You must use Java 11+ for Gradle VM itself.

Try running you build like JAVA_HOME=C:/Users/<my user>/.jdks/openjdk-14.0.1 gradlew.bat clean run.