Convert JSON response into List

Question

I am new to GSON. I need to convert the following JSON response into a List.

JSON response:

{
    "data": [{
        "data": {
            "ac_id": "000",
            "user_id": "000",
            "title": "AAA"
        }
    }, {
        "data": {
            "ac_id": "000",
            "user_id": "000",
            "title": "AAA"
        }
    }]
}

I have a class to cast data

Account. java

public class Account {

     public int ac_id;
     public int user_id;
     public String title;

    @Override
    public String toString(){
         return "Account{"+
         "ac_id="+ac_id+
         ", user_id="+user_id+
         ", title="+title+'}';

    }

}

When I cast the response with my class I get:

[Account{ac_id="000", user_id="000", title="AAA"}, Account{ac_id="000", user_id="000", title="AAA"}]

Now I need to put these two values into a List<Account>.
What do you suggest?

https://github.com/google/gson/blob/master/UserGuide.md#TOC-Collections-Examples — OneCricketeer, Dec 20 '16 at 18:43
http://stackoverflow.com/questions/18544133/parsing-json-array-into-java-util-list-with-gson — Azat Nugusbayev, Dec 20 '16 at 18:46

score 5 · Accepted Answer · edited Dec 20 '16 at 22:32

5

JSONObject data = new JSONObject(response);
JSONArray accounts = data.getJSONArray("data");    
List<Account> accountList = new Gson().fromJson(accounts.toString(), new TypeToken<ArrayList<Account>>(){}.getType());

If you cannot change your JSON response to remove the inner "data" key, you can use this:

Gson gson = new Gson();
ArrayList<Account> accountList = new ArrayList<Account>();
JSONArray accounts = data.getJSONArray("data");  
for (int i = 0; i < accounts.length(); i++) {
  JSONObject a = accounts.getJSONObject(i).getJSONObject("data");
  accountList.add(gson.fromJson(a.toString(), Account.class));
}

edited Dec 20 '16 at 22:32

OneCricketeer

179,855
19
132
245

answered Dec 20 '16 at 18:46

Elias N

1,430
11
19

I'm not sure this will work with the nested `"data"` key – OneCricketeer Dec 20 '16 at 18:47
I get and JsonSyntaxException Expected BEGIN_ARRAY but was BEGIN_OBJECT – user3478224 Dec 20 '16 at 21:55
@user3478224 As other users have mentioned, it's because you have a nested data key. You should have: { "ac_id": "000", "user_id": "000", "title": "AAA" } instead of { "data": { "ac_id": "000", "user_id": "000", "title": "AAA" } } – Elias N Dec 20 '16 at 22:00
@user3478224 see edit if you cannot change your JSON response – Elias N Dec 20 '16 at 22:09
Thank you so much @EliasN your answer works perfect! – user3478224 Dec 21 '16 at 14:06

MezzDroid · Answer 2 · 2016-12-20T20:14:09.723

4

For that you can use Tokens so that gson can understand the custom type...

TypeToken<List<Account>> token = new TypeToken<List<Account>>(){};
List<Account > accountList= gson.fromJson(response, token.getType());

for(Account account : accountList) {
      //some code here for looping  }

edited Dec 20 '16 at 20:14

answered Dec 20 '16 at 18:55

MezzDroid

560
4
11

OneCricketeer · Answer 3 · 2016-12-20T22:34:20.713

1

That nested "data" key is pointless. If you can fix your JSON you should make this instead.

{
    "data": [{
        "ac_id": "000",
        "user_id": "000",
        "title": "AAA"
    }, {
        "ac_id": "000",
        "user_id": "000",
        "title": "AAA"
    }]
}

And then this will work.

JSONObject data = new JSONObject(response);
JSONArray accounts = data.getJSONArray("data");
List<Account> accountList = new Gson()
    .fromJson(accounts.toString(), new TypeToken<ArrayList<Account>>(){}.getType());

Or, again, that first "data" isn't really necessary either.
If you can get your JSON just to be the list of Accounts...

[{
    "ac_id": "000",
    "user_id": "000",
    "title": "AAA"
}, {
    "ac_id": "000",
    "user_id": "000",
    "title": "AAA"
}]

This will work

List<Account> accountList = new Gson()
    .fromJson(response, new TypeToken<ArrayList<Account>>(){}.getType());

edited Dec 20 '16 at 22:34

answered Dec 20 '16 at 18:50

OneCricketeer

179,855
19
132
245

JsonSyntaxException Expected BEGIN_ARRAY but was BEGIN_OBJECT – user3478224 Dec 20 '16 at 21:57
Like I said - It's up to you to fix the actual JSON. Don't just copy the Java code I gave. – OneCricketeer Dec 20 '16 at 21:58
Or you could not use Gson and parse the data yourself. – OneCricketeer Dec 20 '16 at 22:00
I appreciate your help but I can not modify my JSON string, it is working with my all classes with no problem. When I try to convert into an object array is when crashes. – user3478224 Dec 20 '16 at 22:11
How can I parse the data? – user3478224 Dec 20 '16 at 22:14
Use the built-in `JSONObject` class and start parsing it. http://stackoverflow.com/questions/9605913/how-to-parse-json-in-android Of course, you can do the same in Gson but using the otherwise named [`JsonObject`](http://www.javadoc.io/doc/com.google.code.gson/gson/2.8.0) – OneCricketeer Dec 20 '16 at 22:17
You can't modify this one API response to not put `"data":` as part of the response? – OneCricketeer Dec 20 '16 at 22:18
I will try using String.replace to remove the parts that avoid match the form you suggest. – user3478224 Dec 20 '16 at 23:24
That's risky... I think 'Elias N' has the updated answer that should work if you can't edit the JSON on the server-side – OneCricketeer Dec 20 '16 at 23:29

score 0 · Answer 4 · answered Dec 20 '16 at 18:47

0

if you have access to where the JSON was created, i think you should make it like this:

{"data":[{"ac_id":"000","user_id":"000","title":"AAA"},{"ac_id":"000","user_id":"000","title":"AAA"}]}

then to convert it, just use this code: (where jsonString is the string above)

List<Account> accountList = new Gson().fromJson(jsonString, new TypeToken<ArrayList<Account>>(){}.getType());

answered Dec 20 '16 at 18:47

koceeng

2,169
3
16
37

JsonSyntaxException Expected BEGIN_ARRAY but was BEGIN_OBJECT – user3478224 Dec 20 '16 at 21:57
did you change the JSON first? if not then you will get that error – koceeng Dec 21 '16 at 00:51
http://stackoverflow.com/users/6709464/elias-n answer was good, but for me, i think it take too much line of code. I prefer simple way more – koceeng Dec 21 '16 at 00:52

Convert JSON response into List

4 Answers4

Linked