I have a List<Item> collection. I need to convert it into Map<Integer, Item> The key of the map must be the index of the item in the collection. I can not figure it out how to do this with streams. Something like:

items.stream().collect(Collectors.toMap(...));

Any help?

As this question is identified as possible duplicate I need to add that my concrete problem was - how to get the position of the item in the list and put it as a key value

You can create a Stream of the indices using an IntStream and then convert them to a Map :

Map<Integer,Item> map = 
    IntStream.range(0,items.size())
             .boxed()
             .collect(Collectors.toMap (i -> i, i -> items.get(i)));