switch off scientific notation in Gson double serialization

Question

When I use Gson to serialize an Object that contains a double value close to zero it is using the scientific E-notation:

{"doublevaule":5.6E-4}

How do I tell Gson to generate

{"doublevaule":0.00056}

instead? I can implement a custom JsonSerializer, but it returns a JsonElement. I would have to return a JsonPrimitive containing a double having no control about how that is serialized.

Thanks!

Answer 1

Why not provide a new serialiser for Double ? (You will likely have to rewrite your object to use Double instead of double).

Then in the serialiser you can convert to a BigDecimal, and play with the scale etc.

e.g.

    GsonBuilder gsonBuilder = new GsonBuilder();
    gsonBuilder.registerTypeAdapter(Double.class,  new JsonSerializer<Double>() {
        @Override
        public JsonElement serialize(final Double src, final Type typeOfSrc, final JsonSerializationContext context) {
            BigDecimal value = BigDecimal.valueOf(src);

            return new JsonPrimitive(value);
        }
    });

    gson = gsonBuilder.create();

The above will render (say) 9.166666E-6 as 0.000009166666

Answer 2

A minor change on Brian Agnew's answer:

public class DoubleJsonSerializer implements JsonSerializer<Double> {
    @Override
    public JsonElement serialize(final Double src, final Type typeOfSrc, final JsonSerializationContext context) {
        BigDecimal value = BigDecimal.valueOf(src);
        try {
            value = new BigDecimal(value.toBigIntegerExact());
        } catch (ArithmeticException e) {
            // ignore
        }

        return new JsonPrimitive(value);
    }
}