groupping list of objects based on properties in java

Question

I have POJO List<TravelRequestDTO> and I want to group and create filtered List<TravelRequestDTO> if leavingFrom,goingTo,onwarDate,returnDate are same add passenger to same object

Example :

Passanger,     onWard,      return,      leavingFrom,     goingTo

  A,            1-2-20,      3-2-20,        BLR,            PUNE

  B,            1-2-20 ,     3-2-20,        BLR,            PUNE

final List<TravelRequestDTO> should contain :

Passanger,     onWard,      return,      leavingFrom,     goingTo

  A,B          1-2-20      3-2-20        BLR            PUNE

public class TravelRequestDTO {

    private List<Pax> passangers; 
    private String leavingFrom;
    private String goingTo;
    private String onwarDate;
    private String onwardTime;
    private String returnDate;
    private String returnTime;
    private SegmentTypeEnum segmentType;
    private TravelModeEnum travelMode;
    private String purposeOfVisit;
     }


    public class Pax{

    private String name;
    private String age;
    private String mobile;
    }

How do you get Pax object, where does DTO stores information of First passenger — Jatish
– Jatish, Commented Feb 4, 2020 at 5:02
I guess former List<TravelRequestDTO> and later List<TravelRequestDTO> names must be different. — Vishwa Ratna
– Vishwa Ratna, Commented Feb 4, 2020 at 7:58

lczapski · Accepted Answer · 2020-02-04 08:22:37Z

1

If you need older java version, than you can do like this:

Map<Object, List<TravelRequestDTO>> hashMap = new HashMap<Object, List<TravelRequestDTO>>();
for (TravelRequestDTO value: initList) {
    List<Object> key = Arrays.asList(value.getOnWard(),value.getReturn(),value.getLeavingFrom(),value.getGoingTo());
    if (!hashMap.containsKey(key)) {
        List<TravelRequestDTO> list = new ArrayList<TravelRequestDTO>();
        list.add(value);
        hashMap.put(key, list);
    } else {
        hashMap.get(key).add(value);
    }
}

Check this question for other solution.

It is only half way to what you want. After that you have to extract final result from this map. Or you can do it in one step:

Map<Object, TravelRequestDTO> hashMap = new HashMap<Object, TravelRequestDTO>();
for (TravelRequestDTO value: initList) {
    List<Object> key = Arrays.asList(value.getOnWard(),value.getReturn(),value.getLeavingFrom(),value.getGoingTo());
    if (!hashMap.containsKey(key)) {
        TravelRequestDTO item = value; // pass first value or copy it to new
        hashMap.put(key, item);
    } else {
        hashMap.get(key).getPassangers().addAll(value.getPassangers());
    }
}
List<TravelRequestDTO> result = new ArrayList<>(hashMap.values());

edited Feb 4, 2020 at 8:22

answered Feb 4, 2020 at 7:53

lczapski

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1 Comment

lczapski Over a year ago

@abhinandanabhinandan then you can vote up this answer :)

dassum · Accepted Answer · 2020-02-04 05:04:24Z

1

you can use the below code to get a List of TravelRequestDTO objects based on properties.

Function<TravelRequestDTO, List<Object>> compositeKey = travelRecord ->
    Arrays.<Object>asList(travelRecord.getOnWard(),travelRecord.getReturn(),travelRecord.getLeavingFrom(),travelRecord.getGoingTo());

Map<Object, List<TravelRequestDTO>> map =
people.collect(Collectors.groupingBy(compositeKey, Collectors.toList()));

answered Feb 4, 2020 at 5:04

dassum

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2 Comments

abhinandan abhinandan Over a year ago

Thanks for answer, but we need answer for java 1.7

abhinandan abhinandan Over a year ago

Please any one ? help me

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