Combining orElseThrows?

Question

I have the following code and it works as expected:

Optional.ofNullable(testItem.getId())
                .map(testItemRepository::get)
                .orElseThrow(() -> new TestException(ReturnCode.UNKNOWN_ID))
                .orElseThrow(() -> new TestException(ReturnCode.UNKNOWN_ID));

I would like to know if there is a way to just have one orElseThrow-Part or do it less redundant ?

It's hard to tell because it's not clear what `testItemRepository::get` returns (does it return an `Option`?). Try using `flatMap` instead of `map` and remove the last `orElseThrow` line. — Jesper, Nov 16 '20 at 08:04

Nikolas Charalambidis · Accepted Answer · 2020-11-16T09:25:51.870

3

Use Optional#flatMap method that flattens the Optional structure as long the call of the method testItemRepositoryget results in Optional.

 Optional.ofNullable(testItem.getId())
            .flatMap(testItemRepository::get)
            .orElseThrow(() -> new TestException(ReturnCode.UNKNOWN_ID));

I.e. from Optional<Optional<MyObject>> to Optional<MyObect>.

edited Nov 16 '20 at 09:25

answered Nov 16 '20 at 08:06

Nikolas Charalambidis

40,893
16
117
183

score 3 · Answer 2 · answered Nov 16 '20 at 08:07

It seems to be the case that testItemRepository::get returns another Optional<Something>. In that case, you should not use map. Using map will get you a nested optional - Optional<Optional<Something>>, which as you have found out, is not nice to work with. flatMap is made for exactly this situation:

Optional.ofNullable(testItem.getId())
            .flatMap(testItemRepository::get)
            .orElseThrow(() -> new TestException(ReturnCode.UNKNOWN_ID));

flatMap turns an Optional<A> to an Optional<B>, given a Function<A, Optional<B>>.

Combining orElseThrows?

2 Answers2