将默认项添加到流集合

Question

I am performing some actions on a stream and returning an array list. This is working without a problem but I need to do a final step to add an element if the array list is empty (nothing to do with options / nulls just part of the requirement) My way is a bit clunky and I wondered if it can be done in the stream operation instead?

public ArrayList<String> getArrayList () {

        ArrayList<String> aL =  setOfStrings.stream()
            .filter(remove some)
            .filter(remove some more)
            .map(i -> createStringAbout(i))
            .collect(Collectors.toCollection(ArrayList::new));

        if (aL.size() < 1) {
            aL.add("No items passed the test");
        }

        return aL;
    }

So really I would like to do

return set.stream()...

is this possible ?

Answer 1

Use collectingAndThen

.collect(Collectors.collectingAndThen(ArrayList::new, rs -> {
                    if(rs.size() < 1 ) {
                        rs.add("something");
                    }
                   return rs;
                })