“Flatten” Optional in guava and java 7

Question

I'm using guava 20.0 and java 7. I have guava function

public static Function<String, Optional<String>> UP 
        = new Function<String, Optional<String>>() {
    @Override
    public Optional<String> apply(String f) {
        if (f.equals("test"))
            return Optional.absent();
        return Optional.of(f.toLowerCase());
    }
};

This code:

    Optional<String> strNormal = Optional.of("test");
    Optional<String> str = Optional.absent();
    System.out.println("strNormal = " + strNormal.transform(UP));
    System.out.println("str = " + str.transform(UP));

prints:

strNormal = Optional.of(Optional.absent())
str = Optional.absent()

But how can I receive Optional.absent() in both cases. May be there is something like map function for Optional.

Answer 1

Someone already suggested to add this "map" function in Guava 's Optional .However , it is rejected as Optional is considered as legacy and will be frozen.

Your best bet is to write an utility function , something like :

public static Optional<F> transform(Optional<T> optional, Function<T, F> transformer) {
    try {
        return optional.transform(transformer);
    catch (NullPointerException e) {
        return Optional.<F>.absent()
    }
}