How to convert a Map to Arraylist of Objects?

Question

Suppose I have having Json response like this:

{
  "status": true,
  "data": {
    "29": "Hardik sheth",
    "30": "Kavit Gosvami"
  }
}

I am using Retrofit to parse Json response. As per this answer I will have to use Map<String, String> which will give all the data in Map. Now what I want is ArrayList<PojoObject>.

PojoObject.class

public class PojoObject {
    private String mapKey, mapValue;

    public String getMapKey() {
        return mapKey;
    }

    public void setMapKey(String mapKey) {
        this.mapKey = mapKey;
    }

    public String getMapValue() {
        return mapValue;
    }

    public void setMapValue(String mapValue) {
        this.mapValue = mapValue;
    }
}

What is the best way to convert a Map<key,value> to a List<PojoObject>?

why do you need a list in the first place? a map is the better container for the data.. anyway if you really need it just to a simple loop through the map and create your `PojoObject` objects for the list, what exactly is the problem here? — xander, Mar 09 '17 at 12:14

Adowrath · Accepted Answer · 2017-07-07T13:26:10.737

15

If you can expand your class to have a constructor taking the values as well:

map.entrySet()
   .stream()
   .map(e -> new PojoObject(e.getKey(), e.getValue()))
   .collect(Collectors.toList());

If you can't:

map.entrySet()
   .stream()
   .map(e -> {
       PojoObject po = new PojoObject();
       po.setMapKey(e.getKey());
       po.setMapValue(e.getValue());
       return po;
 }).collect(Collectors.toList());

Note that this uses Java 8 Stream API.

edited Jul 07 '17 at 13:26

answered Mar 09 '17 at 12:14

Adowrath

701
11
24

Can we use this stream as reusable like generic function – jebin hector Jan 07 '20 at 11:58
@jebinhector What exactly are you referring to? The result is a List, and if you mean the temporary Stream then no, you cannot reuse Streams. – Adowrath Jan 07 '20 at 13:25

ininprsr · Answer 2 · 2017-03-09T13:02:49.807

Looks like Java has exact POJO Map.Entry like you want. Hence, you can extract the entry set from map and iterate over the entry set like below or you can further convert the set to list like in next snippet and continue with your processing.

 //fetch entry set from map
Set<Entry<String, String>> set = map.entrySet();        

    for(Entry<String, String> entry: set) {
        System.out.println(entry.getKey() +"," + entry.getValue());
    }

    //convert set to list
    List<Entry<String, String>> list = new ArrayList(set);

    for(Entry<String, String> entry: list) {
        System.out.println(entry.getKey() +"," + entry.getValue());
    }

Note that it is not possible to change the key's value with `Map.Entry`, which makes OP's dynamic keys impossible. — Adowrath, Mar 15 '17 at 07:44

ND1010_ · Answer 3 · 2017-03-09T12:34:56.640

-2

Try this

List<Value> list = new ArrayList<Value>(map.values());

Or

hashMap.keySet().toArray(); // returns an array of keys
hashMap.values().toArray(); // returns an array of values

Should be noted that the ordering of both arrays may not be the same.

or

hashMap.entrySet().toArray();

edited Mar 09 '17 at 12:34

answered Mar 09 '17 at 12:13

ND1010_

3,743
24
41

This works if it is a `Map`. If it is a `Map` though, as stated by OP, it will create an `ArrayList`. – Adowrath Mar 09 '17 at 12:16
2

this is wrong. map.values() will return an List of just the values: "Hardik sheth","Kavit Gosvami" – Conffusion Mar 09 '17 at 12:17
The edit did not solve the problem, you still don't have `PojoObject`s. – Adowrath Mar 09 '17 at 14:04

score -3 · Answer 4 · edited Mar 09 '17 at 12:14

-3

You can use this method to convert map to list

List<PojoObject> list = new ArrayList<PojoObject>(map.values());

Assuming:

Map <Key,Value> map;

edited Mar 09 '17 at 12:14

Piyush

18,895
5
32
63

answered Mar 09 '17 at 12:10

Automator1992

116
1
3

1

This works if it is a `Map`. If it is a `Map` though, as stated by OP, it will create an `ArrayList`. – Adowrath Mar 09 '17 at 12:16
This will not work as It Cannot resolve constructor 'ArrayList(java.util.Collection; – Rajesh Jadav Mar 09 '17 at 12:33

score -3 · Answer 5 · answered Mar 09 '17 at 12:24

-3

ArrayList<Map<String,String>> list = new ArrayList<Map<String,String>>();

this may be the best way.

answered Mar 09 '17 at 12:24

AG_

54
3

How to convert a Map to Arraylist of Objects?

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