How to handle a NumberFormatException with Gson in deserialization a JSON response

Question

I\'m reading a JSON response with Gson, which returns somtimes a NumberFormatException because an expected int value is set to an empty string. Now

Answer 1

As stated in another comment, as of GSON 2.3.1 you can register type adapters for primitive types, here is a type adapter that handles int and Integer types, and gracefully defaults to 0 (or null) for strings, booleans and nulls. This will continue to parse strings that have numbers in them like "runtime" : "5".

public static final TypeAdapter<Number> UNRELIABLE_INTEGER = new TypeAdapter<Number>() {
    @Override
    public Number read(JsonReader in) throws IOException {
        JsonToken jsonToken = in.peek();
        switch (jsonToken) {
            case NUMBER:
            case STRING:
                String s = in.nextString();
                try {
                    return Integer.parseInt(s);
                } catch (NumberFormatException ignored) {
                }
                try {
                    return (int)Double.parseDouble(s);
                } catch (NumberFormatException ignored) {
                }
                return null;
            case NULL:
                in.nextNull();
                return null;
            case BOOLEAN:
                in.nextBoolean();
                return null;
            default:
                throw new JsonSyntaxException("Expecting number, got: " + jsonToken);
        }
    }
    @Override
    public void write(JsonWriter out, Number value) throws IOException {
        out.value(value);
    }
};
public static final TypeAdapterFactory UNRELIABLE_INTEGER_FACTORY = TypeAdapters.newFactory(int.class, Integer.class, UNRELIABLE_INTEGER);

You can register it with the following code

Gson gson = new GsonBuilder()
            .registerTypeAdapterFactory(UNRELIABLE_INTEGER_FACTORY)
            .create();

Note that the normal JsonReader.nextInt() that this replaces attempts to call parseInt and parseDouble on the token, so this will replicate internal logic for parsing integers.