Using GSON to parse a JSON array

Question

I have a JSON file like this:

[
    {
        "number": "3",
        "title": "hello_world",
    }, {
        "number": "2",
        "title": "hello_world",
    }
]

Before when files had a root element I would use:

Wrapper w = gson.fromJson(JSONSTRING, Wrapper.class);

code but I can't think how to code the Wrapper class as the root element is an array.

I have tried using:

Wrapper[] wrapper = gson.fromJson(jsonLine, Wrapper[].class);

with:

public class Wrapper{

    String number;
    String title;

}

But haven't had any luck. How else can I read this using this method?

P.S I have got this to work using:

JsonArray entries = (JsonArray) new JsonParser().parse(jsonLine);
String title = ((JsonObject)entries.get(0)).get("title");

But I would prefer to know how to do it (if possible) with both methods.

Are you sure there is comma after title elements? If you remove them `Wrapper[] data = gson.fromJson(jElement, Wrapper[].class);` works fine for me. — Pshemo, Aug 24 '13 at 18:45

Pshemo · Accepted Answer · 2019-08-25T12:26:19.027

117

Problem is caused by comma at the end of (in your case each) JSON object placed in the array:

{
    "number": "...",
    "title": ".." ,  //<- see that comma?
}

If you remove them your data will become

[
    {
        "number": "3",
        "title": "hello_world"
    }, {
        "number": "2",
        "title": "hello_world"
    }
]

and

Wrapper[] data = gson.fromJson(jElement, Wrapper[].class);

should work fine.

edited Aug 25 '19 at 12:26

answered Aug 24 '13 at 18:54

Pshemo

122,468
25
185
269

1

@Snake take a look at [Google Gson - deserialize list object? (generic type)](https://stackoverflow.com/q/5554217) – Pshemo Oct 01 '18 at 08:08
1

@Snake BTW, in case of `jackson` library and [this comment](https://stackoverflow.com/questions/6349421/how-to-use-jackson-to-deserialise-an-array-of-objects#comment37099398_6349488) creating array and wrapping it with `Arrays.asList(..)` is faster than creating a list using TypeRefence. I didn't test it with `gson` library but it may be worth to benchmark it. – Pshemo Oct 01 '18 at 20:59

score 42 · Answer 2 · edited Nov 21 '15 at 21:11

42

Gson gson = new Gson();
Wrapper[] arr = gson.fromJson(str, Wrapper[].class);

class Wrapper{
    int number;
    String title;       
}

Seems to work fine. But there is an extra , Comma in your string.

[
    { 
        "number" : "3",
        "title" : "hello_world"
    },
    { 
        "number" : "2",
        "title" : "hello_world"
    }
]

edited Nov 21 '15 at 21:11

Lord Zed

750
7
28

answered Aug 24 '13 at 19:01

Narendra Pathai

41,187
18
82
120

score 17 · Answer 3 · answered Nov 10 '16 at 08:10

17

public static <T> List<T> toList(String json, Class<T> clazz) {
    if (null == json) {
        return null;
    }
    Gson gson = new Gson();
    return gson.fromJson(json, new TypeToken<T>(){}.getType());
}

sample call:

List<Specifications> objects = GsonUtils.toList(products, Specifications.class);

answered Nov 10 '16 at 08:10

chenyueling

171
1
4

4

For me, this is turning my objects into a List of LinkedTreeMap instead of a List of Specification objects(for example). – Ryan Newsom Nov 15 '16 at 21:12
Where did you get GsonUtils class? – rosu alin Apr 18 '17 at 12:23
``GsonUtils`` is the class where he put his own ``toList()`` method. – user1438038 Oct 12 '17 at 11:17
This cannot work: the TypeToken must create a wrong value since T isn't known when this is compiled. That'll probably create the type token for List – Dr. Hans-Peter Störr Feb 03 '20 at 15:45

score 2 · Answer 4 · answered Dec 04 '19 at 07:47

2

Wrapper[] data = gson.fromJson(jElement, Wrapper[].class);

answered Dec 04 '19 at 07:47

shahzeb khan

21
3

Using GSON to parse a JSON array

4 Answers4

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