how to config gson to exclude 0 integer values

Question

I've a Java class with lot of integer fields and when I want to serialize them to json string due to some of them could have no value, hence after serializing all integers get zero as values ! I want to config gson not to serialize them if they do not have any values.

for example I have this class :

class Example {
   String title = "something";
   int id = 22;
   int userId;
} 

by default gson gives me this result :

{
   "title" : "something",
   "id" : 22,
   "userId" : 0
}

but i don't want the userId to be serialized when its value is 0. so the json should be:

{
   "title" : "something",
   "id" : 22
}

for objects by default gson doesn't serialize null objects is there a way to config gson not to serialize 0 numbers

Answer 1

We have to just use class Integer (Integer javadoc).

class Example {
   String title = "something";
   Integer id = 22;
   Integer userId;
}

Answer 2

Create this JSON type adapter. It can be used where ever you want to ignore writing zero values. It can also be adapted to Long, Double and other numeric types. You can also change it to ignore writing a value other than zero.

Yes I know Autoboxing and Unboxing is implicitly used but you can't specify a primitive type for the generic type.

public class IntIgnoreZeroAdapter extends TypeAdapter<Integer> {
    private static Integer INT_ZERO = Integer.valueOf(0);

    @Override
    public Integer read(JsonReader in) throws IOException {
        if (in.peek() == JsonToken.NULL) {
            in.nextNull();
            return 0;
        }

        return in.nextInt();
    }

    @Override
    public void write(JsonWriter out, Integer data) throws IOException {
        if (data == null || data.equals(INT_ZERO)) {
            out.nullValue();
            return;
        }

        out.value(data.intValue());
    }
}

Change your class to specify the IntIgnoreZeroAdapter for the int members.

class Example {
   String title = "something";

   @JsonAdapter(IntIgnoreZeroAdapter.class)
   int id = 22;

   @JsonAdapter(IntIgnoreZeroAdapter.class)
   int userId;
}