`Thread.currentThread().getContextClassLoader()` is null

Way to reproduce

Just get ClassLoader in Handler

public class HelloServiceHandler implements HelloService.Iface {
    @Override
    public String sayHi(String name) throws TException {
        // classLoader is null
        ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
        return "Hi," + name;
    }
}

Impact

Some third library required Thread.currentThread().getContextClassLoader() to get classloader, this will cause error in service.

Reason

When create Thread, contextClassLoader will get from parent thread, but currently the parent thread is netty thread, there’s no contextClassLoader.

[ikhoon]

there’s multiple co-routines trying to set and unset the contextClassLoader

Are you using Kotlin coroutines with Armeria’s annotated service or gRPC-Kotlin? We may inject a custom coroutine context to push and pop a ContextClassLoader. For example:

• Defines a coroutine context

  class ContextClassLoaderCoroutineContext() : ThreadContextElement<SafeCloseable>, AbstractCoroutineContextElement(Key) {
  
      companion object Key : CoroutineContext.Key<ContextClassLoaderCoroutineContext>
  
      override fun updateThreadContext(context: CoroutineContext): SafeCloseable {
        val currentThread = Thread.currentThread()
        val oldContextClassLoader = currentThread.contextClassLoader
        currentThread.contextClassLoader = javaClass.classLoader
        return SafeCloseable {
          currentThread.contextClassLoader = oldContextClassLoader
        }
      }
  
      override fun restoreThreadContext(context: CoroutineContext, oldState: SafeCloseable) {
        oldState.close()
      }
  }
  

• for gRPC-Kotlin, we can use CoroutineContextServerInterceptor to inject the coroutine context.
• for Armeria annotated service, we can use CoroutineContextService.

[trustin]

As a workaround, you can do this:

public class HelloServiceHandler implements HelloService.Iface {
    @Override
    public String sayHi(String name) throws TException {
        Thread currentThread = Thread.currentThread();
        ClassLoader oldContextClassLoader = currentThread.getContextClassLoader();
        currentThread.setContextClassLoader(getClass().getClassLoader());
        try {
            // ...
        } finally {
            currentThread().setContextClassLoader(oldContextClassLoader);
        }
    }
}

Please let me know if this solves your problem.