Nrthugu

Is it possible to determine whether a GSON JsonElement instance is an integer or is it a float?

I'm able to determine whether it's a number:

JsonElement value = ...

boolean isNumber = value.getAsJsonPrimitive().isNumber();

But how to determine if it's an integer or a float, so I can subsequently use the correct conversion method? Either

float f = value.getAsJsonPrimitive().getAsFloat();

or

int i = value.getAsJsonPrimitive().getAsInt();

Edit: The other question may answer why this may be not implemented in GSON, but this question definitely isn't its duplicate.

use something like, and so if return json object is an instance of float or integer you can then apply the required get:

JSONObject jObj = new JSONObject(jString);

Object aObj = jObj.get("a");

if(aObj instanceof Integer){

    System.out.println(aObj);

}

The only way I've found so far is using regex on a string:

if (value.getAsJsonPrimitive().isNumber()) {

    String num = value.getAsString();

    boolean isFloat = num.matches("[-+]?[0-9]*\.[0-9]+");

    if (isFloat)

        System.out.println("FLOAT");

    else

        System.out.println("INTEGER");

}

This correctly determines 123 as integer, and both 123.45 and 123.0 as floats.

From GSON API docs:

Class JsonElement

...

A class representing an element of Json. It could either be a JsonObject, a JsonArray, a JsonPrimitive or a JsonNull.

and for example:

getAsInt()

convenience method to get this element as a primitive integer value.

JsonElement is not either int or float. You just have the methods to get the value in it somehow casted to some object / primitive.

So your question might better set to something like

Howto check if JsonElement value can be constructed as int or as float

or something like that.

Short answer: it is possible but you need to do it by yourself by checking if from value can be constructed something you need, like other answers suggest.

Gson can not know (of course it can try to guess) what is the type of the object some name holds in JSON. It could be also DateTime serialize to ticks.

Whern using gson.fromJson(...) I would register type adapter like:

JsonDeserializer<Number> numDeserializer = new JsonDeserializer<Number>() {

    @Override

    public Number deserialize(JsonElement json, Type typeOfT

              ,JsonDeserializationContext context) throws JsonParseException {

        try {

            return new Integer(json.getAsString());

        } catch (NumberFormatException nfe) {

            return json.getAsFloat();               

        }

    }

};

and have the corresponding field be Number in my class where i deserialze it.
or if using JsonParser put similar try{} catch {}-block or helper method alike.

But of course these are just some use cases / possibilities.