JNR doesn't respect context classloader

[btiernay]

See jnr/jnr-ffi#51 for the issue.

This could be fixed in the library using something like:

  /**
   * Workaround for unfortunate system class loader usage.
   * 
   * @see https://github.com/jnr/jnr-ffi/issues/51
   */
  @SneakyThrows
  private void patchFfi() {
    ClosureManager closureManager = NativeRuntime.getInstance().getClosureManager();

    // Get inner class loader
    val classLoader = findField(closureManager.getClass(), "classLoader");
    classLoader.setAccessible(true);
    val asmClassLoader = classLoader.get(closureManager);

    // Update to use context class loader over the default system class loader
    val parent = findField(asmClassLoader.getClass(), "parent");
    parent.setAccessible(true);
    parent.set(asmClassLoader, Thread.currentThread().getContextClassLoader());
  }

Thoughts?

[pron]

Can you explain what the problem is?

[btiernay]

If there is a non-standard non-system classloader in play, this causes issues. In my case, I'm using a classloader that knows how to read from nested jars. It is good practice to use context classloader over system for this reason

[pron]

OK, can you submit a PR with the fix?