feat(FeatureClassLoader): support class loading of Java 9+ by bender316 · Pull Request #426

feat(FeatureClassLoader): support class loading of Java 9+ by bender316 · Pull Request #426 · diffplug/spotless

With Java 9 class loading was changed in that way that the bootstrap class loader does not see all classes anymore.
In Java 9+ the platform classloader needs to be used.
A good explanation can be found at http://java9.wtf/class-loading/

fixes #206

It would be great if this fix can be released ASAP as it stalls our migration to Java 11. I'm honestly quite surprised that not more people are affected by this.

With Java 9 class loading was changed in that way that the bootstrap class loader does not see all classes anymore.
In Java 9+ the platform classloader needs to be used.
A good explanation can be found at http://java9.wtf/class-loading/

fixes #206

it stalls our migration to Java 11

If you comment out freshmark, does all of the rest work? Is it only freshmark which is blocked?

I haven't ventured past Java 8 myself yet, so I'm going to rely on the expertise of the rest of the Spotless community to code review this. Looks like spotbugs is upset, run spotbugsMain on your box to see what it's upset about.

@bender316 I'm also a bit surprised that it's taken this long for Java 9+ related issues to appear with Spotless, because I've been using Spotless for Gradle on a Java 11 project without problems for a while now. 🤔

I'll see if I can find the time to review this PR this weekend. :)

If you comment out freshmark, does all of the rest work? Is it only freshmark which is blocked?

Yes. It's not spotless in general which is affected but single formatters. Since we're only using java, groovy and freshmark formatters I can't tell for other formatters.

freshmark breaks because it uses ScriptEngine and javax.script package does not get picked up by the bootstrap classloader anymore.

I think @nedtwigg's review of this PR is great!

@bender316 I personally don't have anything else to add, and if anything I'm probably unqualified to review this PR because even after reading http://java9.wtf/class-loading/, I'm a bit confused as to how we can get references to all the classes in the Java standard library even though they were put into different modules as of Java 9. Is it because we (Spotless) or Gradle uses the classpath rather than the module path?

But regardless, from my point of view, if you're able to apply @nedtwigg's comment, then this PR receives my 👍. :)

I'm a bit confused as to how we can get references to all the classes in the Java standard library even though they were put into different modules as of Java 9. Is it because we (Spotless) or Gradle uses the classpath rather than the module path?

@jbduncan It's because the FeatureClassLoader extends URLClassLoader. If URLClassLoader has no set parent it uses the bootstrap classloader. Prior to Java 9 the bootstrap classloader had access to all classes. Starting with Java 9 it has access to a reduces number of classes. Hence we need to use the platform classloader which can access all classes.

Ok, I added a simple JavaVersion class which parses the version string and provides a getter for the major version. In FeatureClassLoader there is now a check if the version is >= 9 and then calls the getPlatformClassLoader method


		static {
		JAVA_VERSION = System.getProperty("java.version");
		final String[] versionStrings = JAVA_VERSION.split("\\.");