@Override
public Map<Integer, MyObj> getOperationByShipmentIds(Collection<Integer> ids) {
 return storage
   .stream()
   .filter(op -> ids.contains(op.getId()))
   .collect(Collectors.toMap(MyObj::getId, Function.identity()));
}

@Override
public Map<Integer, MyObj> getOperationByShipmentIds(Collection<Integer> ids) {
 return storage
   .stream()
   .filter(op -> ids.contains(op.getId()))
   .collect(Collectors.groupingBy(MyObj::getId));
}

list.values().stream().mapToInt(obj -> obj.getIntField()).sum();

List<MyObject> list = services.stream()
        .flatMap(s -> s.getObjects().stream())
        .collect(Collectors.toList());

import java.util.*;
import java.util.stream.*;
 
class Test {
 public static void main(String[] args) {
  List<String> list = new ArrayList<>();
 
  list.add("Hello");
  list.add("Hello");
  list.add("World");
 
  Map<String, Long> counted = list.stream()
   .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
 
  System.out.println(counted);
 }
}

AtomicInteger counter = new AtomicInteger();
 
stream.collect(groupingBy(x->counter.getAndIncrement()/chunkSize))
 .values()
 .forEach(database::flushChunk);

ListUtils.partition(list, batchSize)