Formatting doubles

[xtian]

When I serialize an array of doubles, I get something like

[16.0,16.0,14.666666666666666,16.22222222222222,15.777777777777779]

In an effort to save bandwidth I implemented a custom serializer that
removes ".0" from integers and keeps 2 decimal digits for numbers
greater than 1.

The result is now the following:

["16","16","14.67","16.22","15.78"]

Almost there, but all numbers have become strings.

I'm stuck here. How to achieve the desired goal?

My code:

NumberFormat doubleFormatter = NumberFormat.getInstance(Locale.US);
doubleFormatter.setMaximumFractionDigits(2);
Gson gson = new GsonBuilder()
.registerTypeAdapter(double.class, new JsonSerializer<Double>() {
public JsonElement serialize(Double value, Type theType,
JsonSerializationContext context) {
String result;
if (value.isInfinite() || value.isNaN() || value.doubleValue()<1)
{
// Small or special values are handled by toString()
result = value.toString();
} else {
// Values greater than 1 are rounded to save bandwidth
result = doubleFormatter.format(value);
}
return new JsonPrimitive(result);
}
}).create();

P.S. someone had a similar problem back in 2008, here:
http://groups.google.com/group/google-gson/browse_thread/thread/51381d16b0bef288/ad09951d165d6cb5?lnk=gst&q=number+formatting#ad09951d165d6cb5

[Pawel Veselov]

Since you are creating JsonPrimitive over a string, the output becomes string.
My suggestion would be to use BigDecimal everywhere and use the necessary precision/scale, or at convert to a big decimal in the custom serializer:
...
return new JsonPrimitive((new BigDecimal(value)).setScale(2, BigDecimal.ROUND_HALF_UP));
...

Thanks,
  Pawel.

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Pawel S. Veselov

[xtian]

Thank you, that's the trick!

My snippet is now the following (just for reference):

private Gson gson = new GsonBuilder()

.registerTypeAdapter(double.class, new JsonSerializer<Double>() {
public JsonElement serialize(Double value, Type theType,
JsonSerializationContext context) {

if (value.isNaN()) {
return new JsonPrimitive(0); // Convert NaN to zero
} else if (value.isInfinite() || value.doubleValue()<1) {
return new JsonPrimitive(value); // Leave small numbers and
infinite alone
} else {
// Keep 2 decimal digits only

return new JsonPrimitive((new BigDecimal(value)).setScale(2,
BigDecimal.ROUND_HALF_UP));
}
}

})
.create();

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