Java with GSON - deserialize only the values into an ArrayList of a JSON string

Question

I have this structure of my JSON response string:

{
    "1":{
        "data1":"1","data2":"test1", ...
    },
    "2":{
        "data1":"6","data2":"test2", ...
    },
    ...
}

And I want to get the values to put into an ArrayList<MyItem>. I use GSON and normally I can do it in this way:

ArrayList<MyItem> items = 
    gson.fromJson(jsonString, new TypeToken<ArrayList<MyItem>>() {}.getType());

The problem is, that it does not work, because my JSON String has numbers as keys, but I only want to get the values to put into the ArrayList (unfortunately, the JSON string can not be changed by myself). How can I do this efficiently?

Why not try to put the json into Map<Integer, ArrayList<MyItem>> map and afterwards List<MyItems> map = foreach(..)? — Sebastian van Wickern
– Sebastian van Wickern, Commented Mar 6, 2013 at 19:55

Programmer Bruce · Accepted Answer · 2013-03-06 21:13:49Z

1

I'd probably deserialize the JSON into a java.util.Map, get the values from the Map as a Collection using the Map.values() method, and then create a new ArrayList using the constructor that takes a Collection.

answered Mar 6, 2013 at 21:13

Programmer Bruce

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1 Comment

Tim Over a year ago

I did it this way. I thought, there is a better solution, but I also did not find one.

Brian Roach · Accepted Answer · 2013-03-06 22:26:57Z

Write a custom deserializer.

class MyItem 
{
    String data1;
    String data2;
    // ...
}

class MyJSONList extends ArrayList<MyItem> {}

class MyDeserializer implements JsonDeserializer<MyJSONList> 
{
    public MyJSONList deserialize(JsonElement je, Type type, JsonDeserializationContext jdc) 
        throws JsonParseException
    {
        MyJSONList list = new MyJSONList();
        for (Entry<String, JsonElement> e : je.getAsJsonObject().entrySet())
        {
            list.add((MyItem)jdc.deserialize(e.getValue(), MyItem.class));
        }

        return list;
    }

}

Example:

String json = "{\"1\":{\"data1\":\"1\",\"data2\":\"test1\"},\"2\":{\"data1\":\"6\",\"data2\":\"test2\"}}";
Gson g = new GsonBuilder()
            .registerTypeAdapter(MyJSONList.class, new MyDeserializer())
            .create();
MyJSONList l = g.fromJson(json, MyJSONList.class);


for (MyItem i : l)
{
    System.out.println(i.data2);
}

Output:

test1
test2

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