def get_mapper_instance(env):
    global mapper_instance
    if not mapper_instance:
        fqcn = env.get_property(DEFAULT_CONFIG_FILE, PROPERTY_MAPPER_CLASS, DEFAULT_MAPPER_CLASS)
        env.log("Creating a new mapper instance of {}".format(fqcn))
        klass = find_class(fqcn)
        mapper_instance = klass(env)
    return mapper_instance