URLClassLoader.findClass with different behavior when called within jjs Nashorn

[brunoborges]

When running a script with jjs that invokes a class from a classpath configured with 'jjs -cp', that will make use of URLClassLoader.findClass, the behavior is different from when the Java library is invoked the usual way.

See log trace: https://gist.github.com/brunoborges/110af2969f2c2be7e288

To invoke code, see: https://github.com/brunoborges/nashorn/tree/master/maven/samples/springboot

[philwebb]

That's weird, I wonder why URLClassLoader.findClass wouldn't find that class.

[brunoborges]

That can be a bug in:

1. URLClassLoader.findClass weird behavior when called from within Nashorn script executed with *jjs
2. Nashorn's way to build a ClassLoader for the -cp classpath passed by with jjs
3. Spring Boot usage of findClass, plus some weird bug inside findClass

Of course 3 is likely not true :-) #ButWhoKnows

[wilkinsona]

When launched with jjs -cp, Nashorn creates a ClassLoader using the specified class path but, unlike java -cp, it does not make that ClassLoader the thread context class loader. This means we end up trying to load classes using the app class loader which can't see any of the classes that are on the class path.

Setting the thread context class loader before calling run() fixes the problem:

var SpringApplication = Packages.org.springframework.boot.SpringApplication;
java.lang.Thread.currentThread().contextClassLoader = SpringApplication.class.classLoader;