Flatmap nested collection

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Category:Languages

I have a list of objects, some of them can be collections. I would like to get a stream of plain objects.

List<Object> objects = List.of(1, 2, "SomeString", List.of(3, 4, 5, 6),      7, List.of("a", "b", "c"),     List.of(8, List.of(9, List.of(10)))); 

I would like to get a stream with elements.

1, 2, "SomeString", 3, 4, 5, 6, 7, "a", "b", "c", 8, 9, 10 

I have tried

Function<Object, Stream<Object>> mbjectToStreamMapper = null; //define it. I have not figured it out yet! objects.stream().flatMap(ObjectToStreamMapper).forEach(System.out::println); 

I also checked an example which shows how to use a recursive function which flattens a collection. However, in this example .collect(Collectors.toList()); used to keep an intermediate result. Collectors.toList() is a terminal operation, which will start processing the stream right away. I would like to get a stream, which I can iterate on later.


Update

I agree with comments, it is a terrible idea to have a stream composed of objects of different nature. I just wrote this question for simplicity. In real life, it can be that I listen to different events, and process some business objects from incoming streams, some of them can send stream of objects, other - just single objects.

 


We can recursively get the nested stream if the object being traversed is an instance of Collection.

public static void main(String args[]) {        List<Object> objects = List.of(1, 2, "SomeString", List.of(3, 4, 5, 6),             7, List.of("a", "b", "c"),             List.of(8, List.of(9, List.of(10))));        List<Object> list = objects.stream().flatMap(c -> getNestedStream(c)).collect(Collectors.toList()); }  public static Stream<Object> getNestedStream(Object obj) {     Collection c;     if(obj instanceof Collection){         c = (Collection)obj;         return c.stream().flatMap((coll) -> getNestedStream(coll));     }     return Stream.of(obj); } 

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