build: fix google-java-format for all java versions

build.gradle

@@ -64,13 +64,7 @@ spotless {
 
 		importOrderFile 'config/code-formatter/eclipse.importorder'
 		eclipse().configFile 'config/code-formatter/eclipse.xml'
-		if (JavaVersion.current() < JavaVersion.VERSION_16) {
-			removeUnusedImports()
-		} else {
-			// google-format on Java 16+ issue: https://github.com/diffplug/spotless/issues/834
-			println('Warning! Unused imports remove is disabled for Java 16+'
-					+ ' (use workaround from https://github.com/diffplug/spotless/tree/main/plugin-gradle#google-java-format)')
-		}
+		removeUnusedImports()
 
 		lineEndings(com.diffplug.spotless.LineEnding.UNIX)
 		encoding("UTF-8")

gradle.properties

 org.gradle.warning.mode=all
 org.gradle.parallel=true
+
+# Flags for google-java-format (optimize imports by spotless) for Java >= 16.
+# Java < 9 will ignore unsupported flags (thanks to -XX:+IgnoreUnrecognizedVMOptions)
+org.gradle.jvmargs=-XX:+IgnoreUnrecognizedVMOptions \
+  --add-exports='jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED' \
+  --add-exports='jdk.compiler/com.sun.tools.javac.file=ALL-UNNAMED' \
+  --add-exports='jdk.compiler/com.sun.tools.javac.parser=ALL-UNNAMED' \
+  --add-exports='jdk.compiler/com.sun.tools.javac.tree=ALL-UNNAMED' \
+  --add-exports='jdk.compiler/com.sun.tools.javac.util=ALL-UNNAMED'