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How can I prevent gson from converting integers to doubles

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再見小時候
再見小時候 2020-12-05 07:37

I\'ve got integers in my json, and I do not want gson to convert them to doubles. The following does not work:

@Test
public void keepsIntsAsIs(){
    String
6条回答
  • 谎友^
    谎友^ (楼主)
    2020-12-05 08:28

    1) You have to create custom JsonDeserializer and not JsonSerializer like in your question.

    2) I don't think this behavior comes from Double deserializer. it is more like json object/map problem

    Here is from source code: 

    case NUMBER:
      return in.nextDouble();

    So you can try approach with custom deserializer for Map (or some more generic map if you want) :

    public static class MapDeserializerDoubleAsIntFix implements JsonDeserializer>{

    @Override  @SuppressWarnings("unchecked")
    public Map deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        return (Map) read(json);
    }

    public Object read(JsonElement in) {

        if(in.isJsonArray()){
            List list = new ArrayList();
            JsonArray arr = in.getAsJsonArray();
            for (JsonElement anArr : arr) {
                list.add(read(anArr));
            }
            return list;
        }else if(in.isJsonObject()){
            Map map = new LinkedTreeMap();
            JsonObject obj = in.getAsJsonObject();
            Set> entitySet = obj.entrySet();
            for(Map.Entry entry: entitySet){
                map.put(entry.getKey(), read(entry.getValue()));
            }
            return map;
        }else if( in.isJsonPrimitive()){
            JsonPrimitive prim = in.getAsJsonPrimitive();
            if(prim.isBoolean()){
                return prim.getAsBoolean();
            }else if(prim.isString()){
                return prim.getAsString();
            }else if(prim.isNumber()){

                Number num = prim.getAsNumber();
                // here you can handle double int/long values
                // and return any type you want
                // this solution will transform 3.0 float to long values
                if(Math.ceil(num.doubleValue())  == num.longValue())
                   return num.longValue();
                else{
                    return num.doubleValue();
                }
           }
        }
        return null;
    }
}



    To use it you will have to give proper TypeToken to registerTypeAdapter and gson.fromJson function:
    


    String json="[{\"id\":1,\"quantity\":2,\"name\":\"apple\"}, {\"id\":3,\"quantity\":4,\"name\":\"orange\"}]";

GsonBuilder gsonBuilder = new GsonBuilder();

gsonBuilder.registerTypeAdapter(new TypeToken>(){}.getType(),  new MapDeserializerDoubleAsIntFix());

Gson gson = gsonBuilder.create();
List> l = gson.fromJson(json, new TypeToken>>(){}.getType() );

for(Map item : l)
    System.out.println(item);

String serialized = gson.toJson(l);
System.out.println(serialized);

    


    Result:
    


    {id=1, quantity=2, name=apple}
{id=3, quantity=4, name=orange}
Serialized back to: [{"id":1,"quantity":2,"name":"apple"},{"id":3,"quantity":4,"name":"orange"}]

    


    


    PS: It is just one more option you can try. Personally i feel like creating custom object for your json instead of List> is much cooler and easier to read way
    
    
    
             
    
                                                        
    
            
            
    
              
                
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