Java 8 throw exception if stream returns no results

Question

I am curious if it's possible to use orElseThrow() in the following situation or if there a more Java 8 way to do the equivalent of this as a 1-liner?

Collection<Foo> foo = blah.stream().filter(somePredicate).collect(Collectors.toList());
if (foo.isEmpty()) {
  throw new Exception("blah");
}

maybe Collectors.collectingAndThen() method can help. – Spasoje Petronijević Jul 03 '19 at 12:16 — Spasoje Petronijević, Jul 03 '19 at 12:16

jannis · Accepted Answer · 2019-07-03T12:28:51.190

10

You could try this:

Collection<Foo> foo = blah.stream().filter(somePredicate)
    .collect(Collectors.collectingAndThen(Collectors.toList(), Optional::of))
    .filter(l -> !l.isEmpty())
    .orElseThrow(() -> new Exception("blah"))

Note that comparing to your code this allocates an extra Optional instance.

edited Jul 03 '19 at 12:28

answered Jul 03 '19 at 12:18

jannis

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Gotcha, thanks. I think I'll stick with the original but it's good to know this option exists – ekjcfn3902039 Jul 03 '19 at 13:20

Java 8 throw exception if stream returns no results

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