Java 8 lambda for each call method and addAll

Question

I would like to replace the following code to utilize Java 8 streams if possible:

final List<Long> myIds = new ArrayList<>();
List<Obj> myObjects = new ArrayList<>();
// myObject populated...

for (final Obj ob : myObjects) {
   myIds.addAll(daoClass.findItemsById(ob.getId()));
}

daoClass.findItemsById returns List<Long>

Can anybody advise the best way to do this via lambdas? Many thanks.

John Kugelman · Accepted Answer · 2018-04-30 16:46:38Z

11

List<Long> myIds = myObjects.stream()
    .map(Obj::getId)
    .map(daoClass::findItemsById)
    .flatMap(Collection::stream)
    .collect(Collectors.toList());

answered Apr 30, 2018 at 16:46

John Kugelman

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Comments

Hemant Patel · Accepted Answer · 2018-04-30 17:38:44Z

2

Use flatMap which combines multiple list into a single list.

myObjects.stream()
    .flatMap(ob -> daoClass.findItemsById(ob.getId()).stream())
    .collect(Collectors.toList());

edited Apr 30, 2018 at 17:38

answered Apr 30, 2018 at 16:46

Hemant Patel

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Comments

Ousmane D. · Accepted Answer · 2018-04-30 16:52:58Z

1

flatMap it!

source.stream()
      .flatMap(e -> daoClass.findItemsById(e.getId).stream())     
      .collect(Collectors.toCollection(ArrayList::new));

answered Apr 30, 2018 at 16:52

Ousmane D.

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