【转】How can I prevent gson from converting integers to doubles

处理Gson中，json转换map造成的int变double的问题。

原文链接

MapDeserializerDoubleAsIntFix.java

/**
*最近在研究网络请求数据解析的问题，发现json数据被强制转换为map结构的时候，会出现int变成double的问题
*在stackoverflow上看到了一个这个How can I prevent gson from converting integers to doubles 的问题，采用了这个答案
*https://stackoverflow.com/a/36529534/5279354答案
*/

import com.google.gson.JsonArray;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonObject;
import com.google.gson.JsonParseException;
import com.google.gson.JsonPrimitive;
import com.google.gson.internal.LinkedTreeMap;

import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.Set;

public class MapDeserializerDoubleAsIntFix implements JsonDeserializer<Map<String, Object>> {


    @Override
    public Map<String, Object> deserialize(JsonElement jsonElement, Type type, JsonDeserializationContext jsonDeserializationContext) throws JsonParseException {
        return (Map<String, Object>) read(jsonElement);
    }

    public Object read(JsonElement in) {
        if(in.isJsonArray()){
            List<Object> list = new ArrayList<>();
            JsonArray arr = in.getAsJsonArray();
            for (JsonElement anArr : arr) {
                list.add(read(anArr));
            }
            return list;
        }else if(in.isJsonObject()){
            Map<String, Object> map = new LinkedTreeMap<String, Object>();
            JsonObject obj = in.getAsJsonObject();
            Set<Map.Entry<String, JsonElement>> entitySet = obj.entrySet();
            for(Map.Entry<String, JsonElement> 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;
    }


    @Test
    public void test2() {
        String json = "{\"data\":[{\"id\":1,\"quantity\":2,\"name\":\"apple\"}, {\"id\":3,\"quantity\":4,\"name\":\"orange\"}]}";
        System.out.println("json == " + json);
//        Map<String, Object> map = new LinkedTreeMap<>();
//        map = new Gson().fromJson(json, map.getClass());
//        System.out.println(map);

        GsonBuilder gsonBuilder = new GsonBuilder();
        gsonBuilder.registerTypeAdapter(new TypeToken<Map <String, Object>>(){}.getType(),  new MapDeserializerDoubleAsIntFix());
        Gson gson = gsonBuilder.create();
        Map<String, Object> map = gson.fromJson(json, new TypeToken<Map<String, Object>>(){}.getType());
        System.out.println(map);
    }
}

参考文章

https://gist.github.com/xingstarx/5ddc14ff6ca68ba4097815c90d1c47cc

https://blog.csdn.net/ligeforrent/article/details/93759524