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
– Pshemo, Commented Aug 24, 2013 at 18:45

Pshemo · Accepted Answer · 2019-08-25 12:26:19Z

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, 2019 at 12:26

answered Aug 24, 2013 at 18:54

Pshemo

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2 Comments

Pshemo Over a year ago

@Snake take a look at Google Gson - deserialize list<class> object? (generic type)

Pshemo Over a year ago

@Snake BTW, in case of jackson library and this comment 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.

Lord Zed · Accepted Answer · 2015-11-21 21:11:06Z

43

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, 2015 at 21:11

Lord Zed

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answered Aug 24, 2013 at 19:01

Narendra Pathai

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Comments

chenyueling · Accepted Answer · 2016-11-10 08:10:39Z

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, 2016 at 8:10

chenyueling

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4 Comments

Ryan Newsom Over a year ago

For me, this is turning my objects into a List of LinkedTreeMap instead of a List of Specification objects(for example).

rosu alin Over a year ago

Where did you get GsonUtils class?

user1438038 Over a year ago

GsonUtils is the class where he put his own toList() method.

Dr. Hans-Peter Störr Over a year ago

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<Object>. You'd have to use the actual class when creating the type.

shahzeb khan · Accepted Answer · 2019-12-04 07:47:52Z

2

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

answered Dec 4, 2019 at 7:47

shahzeb khan

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