private static boolean isKeyArnFormat(String keyArn) {
    List<String> tokens = Splitter.on(':').splitToList(keyArn);
    return tokens.size() == 6 && tokens.get(5).startsWith("key/");
  }
Returns {@code true} if {@code keyArn} is in key ARN format.
java_src/src/main/java/com/google/crypto/tink/integration/awskms/AwsKmsAead.java