gson: deserialize json with composite keys

Question

I would like to use this kind of Objects with json:

class Message{
    int code;
    String user;
    Map<List<String>, List<String>> profile;
}

it seems json can't handle Object keys as array, so I would need to tranfer them like that:

{
"code": 1,
"user": "John",
"profile": {
    "type,1": ["tester"],
    "lang,2": ["fr", "it", "en", "sp"],
    "rate,4": ["10", "1000"],
    "date,5": ["134118329", "1341973211"]

    }
}

or

{
"code": 1,
"user": "John",
"profile": {
    "type": [1,"tester"],
    "lang": [2,"fr", "it", "en", "sp"],
    "rate": [4,"10", "1000"],
    "date": [5,"134118329", "1341973211"]

    }
}

the first json is probably simpler, even if it relies on a hard string separator,

So with the first one it seems I have to write this huge adapter:

private static class MyAdapter implements JsonSerializer<Map<List<String>, List<String>>>,
        JsonDeserializer<Map<List<String>, List<String>>> {

    @Override   
    public JsonElement serialize(Map<List<String>, List<String>> m,
            Type type, JsonSerializationContext context) {

        JsonObject j = new JsonObject();
        for (Entry<List<String>, List<String>> e : m.entrySet() ){
            JsonArray jj=new JsonArray();
            for (String s : e.getValue()){
                jj.add(new JsonPrimitive(s));
            }
            j.add(e.getKey().get(0)+","+e.getKey().get(1), jj);
        }
        return j;
    }

    @Override
    public Map<List<String>, List<String>> deserialize(JsonElement json, Type type,
            JsonDeserializationContext arg2) throws JsonParseException {

        Map<List<String>, List<String>> m = new HashMap<List<String>, List<String>>();

        JsonObject jObject = json.getAsJsonObject();
        for (Entry<String, JsonElement> e : jObject.entrySet() ){
            List<String> key = new ArrayList<String>();
            List<String> value = new ArrayList<String>();
            for (String s : e.getKey().split(",") ){
                key.add(s);
            }
            for (JsonElement jj : e.getValue().getAsJsonArray() ){
                value.add(jj.getAsString());
            }
            m.put(key, value);
        }
        return m;
    }
}

...

GsonBuilder g = new GsonBuilder();
    g.registerTypeAdapter(Map.class, new MyAdapter());
    Gson gson = g.create();

Is there faster ways? I guess yes, the idea is just to split the key into a Map composite key, because each part of the key has an important meaning

thx, and sry for the edit

right the json is invalid (jslint), let me correct the question, Done corrected — , Jul 13 '12 at 20:10

Francisco Spaeth · Accepted Answer · 2012-07-13T20:16:10.937

1

This will not work.

Object declaration syntax according specification:

An object is an unordered set of name/value pairs. An object begins with { (left brace) and ends with } (right brace). Each name is followed by : (colon) and the name/value pairs are separated by , (comma).

This:

{
    ["type", 1]: "tester",
    ["lang", 2]: ["fr", "it", "en", "sp"],
    ["rate", 4]: ["10", "1000"],
    ["date", 5]: ["134118329", "1341973211"]

}

is invalid, and therefore you can't read with Gson causing the following exception: com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING

the name in front of json: aRequest = is invalid too.

edited Jul 13 '12 at 20:16

answered Jul 13 '12 at 20:03

Francisco Spaeth

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how could I do composite keys in Json? – Jul 13 '12 at 20:09
1

{"key":["a","b"],"value":12} wouldn't be enough? – Francisco Spaeth Jul 13 '12 at 20:10
and with more than one it gives an Array? possible to deserialize it it in a Map? ["a", "b"] as key – Jul 13 '12 at 20:17
no, the key property would be mapped to the Map key as list... just in the representation would be presented as a property named key – Francisco Spaeth Jul 13 '12 at 20:18
I don't understand, the idea is to have {"key":["a","b"],"value":12}, {"key":["a","c"],"value":14}, ... How would you put them in a KeyValue Map, to me you just can use arrays with that, BTw thx, I edited almost completely the question could you have a look again sry – Jul 14 '12 at 12:10

score 1 · Answer 2 · edited May 23 '17 at 10:34

1

For profile values, I don't know if there is better than Object unfortunately

It looks like a List<String> or String[] would be a natural fit, with special handling for the single value entry that is not in a list format.

Unfortunately, the issue of deserializing a JSON structure that is sometimes a list and sometimes an object has come up repeatedly on SO. Fortunately, so have solutions.

edited May 23 '17 at 10:34

Community

1
1

answered Jul 13 '12 at 20:23

Programmer Bruce

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The question of this post was quite a moving target, with three different (changing) JSON structures. Is there still an open question? – Programmer Bruce Jul 23 '12 at 22:51
yes right the Q changed too much, now I'm just facing how to best manage a (a,b) composite key in Json which is not supported, it could be a new Q, thx your answer was helpful – Jul 24 '12 at 20:11

gson: deserialize json with composite keys

2 Answers2