Java – enables gson to deserialize numbers to integers or doubles

I'm sorry for gson

I have a simple JSON. I want to deserialize it into map < string, Object >

I'm really intuitive. 123 should be parsed as int (or long) and 123.4 as float (or double)

On the other hand, gson has been creating doubles

Can I tell gson not to abuse double all the time?

My actual code:

Type mapType = new TypeToken<Map<String,Object>>() {}.getType();
GSON gson = new Gson();
Map<String,Object> map = gson.fromJson(someString,mapType);

Solution

The following code compiles & Works:

package test;

import java.lang.reflect.Type;
import java.text.NumberFormat;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import com.google.gson.reflect.TypeToken;

public class Main {

    public static void main(String[] args) {
        GsonBuilder builder = new GsonBuilder();
        builder.registerTypeAdapter(Object.class,new MyObjectDeserializer());
        Gson gson = builder.create();
        String array = "[1,2.5,4,5.66]";

        Type objectListType = new TypeToken<ArrayList<Object>>() {}.getType();
        List<Object> obj = gson.fromJson(array,objectListType);

        System.out.println(Arrays.toString(obj.toArray()));
    }

    public static class MyObjectDeserializer implements JsonDeserializer<Object> {

        public Object deserialize(JsonElement json,Type typeOfT,JsonDeserializationContext context) 
            throws JsonParseException {

          Number num = null;
          try {
              num = NumberFormat.getInstance().parse(json.getAsJsonPrimitive().getAsString());
          } catch (Exception e) {
              //ignore
          }
          if (num == null) {
              return context.deserialize(json,typeOfT);
          } else {
              return num;
          }
      }
    }

}

My solution will first try to parse strings into numbers, and if it fails, it will let the standard gson deserializer complete its work

If you need a locale neutral number parser, use this method to parse numbers:

private static Number parse(String str) {
    Number number = null;
    try {
        number = Float.parseFloat(str);
    } catch(NumberFormatException e) {
    try {
        number = Double.parseDouble(str);
    } catch(NumberFormatException e1) {
        try {
            number = Integer.parseInt(str);
        } catch(NumberFormatException e2) {
            try {
                number = Long.parseLong(str);
            } catch(NumberFormatException e3) {
                throw e3;
            }       
        }       
    }       
}
    return number;
}