Is it possible to change order of attributes when toJson()?

Question

Let's take this example. I have a pojo class as below.

public class MyRecord{
    private String name;
    private String id;

    //constructors and getters,setters
}

when I get the toJson(new MyRecord("MyName","myId") output for above I can get.

{
  "name": "MyName",
  "id": "123" 
}

And I have inherited one as follows to add the dateTime.

public class MyRecordWithDateTime extends MyRecord{
        private String DateTime;           

        //constructors and getters,setters
}

so when I called toJson(new MyRecordWithDateTime("2016-01-01", "MyName", "myId"))

The output is this

{
  "name": "MyName",
  "id": "123",
  "dateTime": "2016-01-01" 
}

but I actually need that as follows. (dateTime should come first.)

{          
  "dateTime": "2016-01-01", 
  "name": "MyName",
  "id": "123"
}

Is there anyway to do that with keeping inheritance?

Object fields/members do not have an order (nor should they). If you need members ordered you should use a list/array structure — Richard H, Aug 10 '16 at 07:34
@RichardH if you have looked closely Json.toJson() extracts fields by getters and exactly follows the order of getters. i.e. If you skip a getter for some field, it will not appear. The reason I asked this is, I wonder whether there are any annotation at least. — Supun Wijerathne, Aug 10 '16 at 07:38
Relying on the order in which the getters are written in your class is terrible design. You'd be better off calling the getters yourself in the order you want — Richard H, Aug 10 '16 at 07:41
But that's how JSON.toJson() works. It's the library implementation and I cannot do anything about that. The problem about changing the order is "How can I do that for an inherited class?" as in my example. It extracts the parent class getters first. — Supun Wijerathne, Aug 10 '16 at 07:46
But that is my point: class fields do not have an order. If you want fields or values ordered you need to use a data structure that has an order, i.e an array, list or ordered hash of some sort. — Richard H, Aug 10 '16 at 07:59
@Yazan its just for presentation purpose. Indeed there is a front-end client who can work with this json, without worrying about the order. But if we refer the rest service directly anyway, the order I want, is pretty clear to understand. :) — Supun Wijerathne, Aug 10 '16 at 08:42

score 3 · Answer 1 · answered Feb 12 '21 at 01:25

3

Maybe kinda late but just in case there is this annotation @JsonPropertyOrder

answered Feb 12 '21 at 01:25

RoCaSo

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Souin · Answer 2 · 2016-08-10T07:35:07.433

1

Before you put it in your JSON file, you can try to make an ordered List ( LinkedList, ArrayList or something like), then sort it as you want and after that put it in JSON.

But obviously, a better idea than mine exists!!

But the fact is: JSON doesn't need to be sorted! You just use the getter and it will find your value associated to the key! Even if it's in the last position.

edited Aug 10 '16 at 07:35

answered Aug 10 '16 at 07:33

Souin

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I can't get you. I want to change the order of fields?? – Supun Wijerathne Aug 10 '16 at 07:34
1

Just use a list in your constroctor. Something like : `private LinkedList – Souin Aug 10 '16 at 07:37
I can use a List as you propose, but that changes the response format in terms of indentation right? – Supun Wijerathne Aug 10 '16 at 07:40
1

Imagine you have you LinkedHashMap (name : linkHM) sorted and completed properly : `JSONObject jo = new JSONObject(); for (Map.Entry elem : linkHM.entrySet()) { jo.put(elem.getKey(),elem.getValue()); }` – Souin Aug 10 '16 at 07:44
But to do that, I should completely move from object nature right? which is some what conflicting. – Supun Wijerathne Aug 10 '16 at 08:48
I can't understand what you said. I didn't tried what I said, but I think it could work. The order: (1)you initialize the LinkedHashMap, (2)you put the elements in the order ( with name as the key, and the value as a string (or not, Json preserves the type)) (3) you create the JSONObject with the for statement I posted above, and (4) your write the JSONObject into the file! – Souin Aug 10 '16 at 09:23

score 1 · Accepted Answer · answered Aug 10 '16 at 08:07

1

Field/member/attributes in a JSON collection do not have an order, and as far as this JSON data structure is concerned, the "order" doesn't matter.

The only reason I can imagine you are concerned with the order is for printing/presentation purposes. In that case I suggest you manually construct the JSON string yourself.

answered Aug 10 '16 at 08:07

Richard H

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So does your answer implicitly suggest that ->"Don't worry about the order of keys, at all when you creating JSON responses" ??? – Supun Wijerathne Aug 10 '16 at 08:44
1

Correct. JSON is just a string representation of a javascript object. The order of keys in a javascript object absolutely does not matter - indeed there is no order defined. If you want to print out a JSON string with the keys in a particular order you'll have to implement this yourself instead of relying on a library method. – Richard H Aug 10 '16 at 11:58

Is it possible to change order of attributes when toJson()?

3 Answers3