How can I save a Future instance for later use

Assume I have a method that returns a Future. For example:

void foo() {
    final Future<String> future = bar();
    save(future, "FOO");
}

void fooCancel() {
    final Future<String> future = load("FOO");
    future.cancel();
}

Is there a good way to persist the future? I could use something simple like a Map<String, Future> but that seems like a really bad idea.