Transform List of object to a Map in java-CodePudding

I have a list of item List<Item> resultBl like below :

id = 18003  amount = 128 nameType = SUBMITTED
id  = 18189 amount = 95 nameType = SUBMITTED
id  = 18192 amount = 160 nameType = POSITIVE
id  = 18192 amount = 30 nameType = DRAFT
id  = 18192 amount = 873 nameType = SUBMITTED
id  = 18237 amount = 390 nameType = POSITIVE
id  = 18237 amount = 60 nameType = DRAFT
id  = 18237 amount = 2731 nameType = SUBMITTED

I want to transform this list to a map with this form, the key is the id and the value is a list of objects :

Map<Integer,List<ItemDetails>>  mapTest= new HashMap<Integer,List<ItemDetails>>();

[18237 , [amount = 390 ,nameType = POSITIVE],[amount = 60 nameType = DRAFT], [amount = 2731 nameType = SUBMITTED]], ...

I tried with different ways but always I had a repeated elements :

   List<Integer> ids2 = new ArrayList<Integer>();
    List<Integer> ids = new ArrayList<Integer>();

    for(Item item: resultBl) {
         ids.add(item.getId());
     }
     ids2 =ids.stream().distinct().collect(Collectors.toList());
     Map<Integer,List<ItemDetails>>  mapTest= new HashMap<Integer,List<ItemDetails>>();
     List<ItemDetails> itemDetailsList = new ArrayList<ItemDetails>();
      for(Integer s:ids2) {
         for(Item i : resultBl) {
              if(s.equals(i.getId())) {
                ItemDetails it =new ItemDetails();
                it.setAmount(i.getAmount());
                it.setNameType(i.getNameType()) ;
                itemDetailsList .add(it);
                }
           }
          mapTest.put(s, itemDetailsList);
         }

CodePudding user response：

I would use streams and groupingBy to do this.

When you have a list of your items resultBl all you have to do is

Map<Integer, List<Item>> resultMap = resultBl.stream().collect(groupingBy(Item::getId, toList()));

imports:

import static java.util.stream.Collectors.groupingBy;
import static java.util.stream.Collectors.toList;

This will group your items by the id parameter.

CodePudding user response：

Map<Integer,List<Item>>  map = resultBL.stream(Collectors.toMap(Item::getId, Function.identity()));

It is Lambda. Java version >= 8