@Override
  public ImmutableMap<String, ?> defaultValues(Map<String, ?> userProvidedDefaults) {
    Object userProvidedOwner = userProvidedDefaults.get("owner:owner");

    UserPrincipal owner = DEFAULT_OWNER;
    if (userProvidedOwner != null) {
      if (userProvidedOwner instanceof String) {
        owner = createUserPrincipal((String) userProvidedOwner);
      } else {
        throw invalidType("owner", "owner", userProvidedOwner, String.class, UserPrincipal.class);
      }
    }

    return ImmutableMap.of("owner:owner", owner);
  }
Attribute provider that provides the {@link FileOwnerAttributeView} ("owner").

@author Colin Decker
jimfs/src/main/java/com/google/common/jimfs/OwnerAttributeProvider.java