@staticmethod
def _jar_id(jar):
    """Create a string identifier for the IvyModuleRef key.

        :param IvyModuleRef jar: key for a resolved jar
        :returns: String representing the key as a maven coordinate
        """
    if jar.rev:
        return '{0}:{1}:{2}'.format(jar.org, jar.name, jar.rev)
    else:
        return '{0}:{1}'.format(jar.org, jar.name)
