How to look up value in a list of map?

Assuming you want to look into each Map in List and check for both keys in nested maps, you can do something like below -

OptionalLong optional = listOfMap.stream().filter(x -> x.containsKey(1) && x.get(1).containsKey(10)).mapToLong(x -> x.get(1).get(10)).findFirst();
if (optional.isPresent()) {
  return optional.getAsLong();
}

Use stream to iterate over list and filter elements containing maps with required values and return first element matching out criteria.

For aggregating, instead of findFirst(), you can reduce by adding starting with 0 as identity.

long l = listOfMap.stream().filter(x -> x.containsKey(1) && x.get(1).containsKey(10)).mapToLong(x -> x.get(1).get(10)).reduce(0L, (left, right) -> left + right);