Gson转换导致int转为double问题解决

当我们用Object或者Map中的泛型使用了Object,我们将json转换之后,发现数据中的所以数值都变成了double类型,0变为了0.0,导致后续程序可能出现一些问题。

查看Gson的源码, 会发现Object最后默认的TypeAdapter使用的是com.google.gson.internal.bind包下的ObjectTypeAdapter,里边的处理如下:

/**
 * Adapts types whose static type is only 'Object'. Uses getClass() on
 * serialization and a primitive/Map/List on deserialization.
 */
public final class ObjectTypeAdapter extends TypeAdapter {
  public static final TypeAdapterFactory FACTORY = new TypeAdapterFactory() {
    @SuppressWarnings("unchecked")
    @Override public  TypeAdapter create(Gson gson, TypeToken type) {
      if (type.getRawType() == Object.class) {
        return (TypeAdapter) new ObjectTypeAdapter(gson);
      }
      return null;
    }
  };

  private final Gson gson;

  ObjectTypeAdapter(Gson gson) {
    this.gson = gson;
  }

  @Override public Object read(JsonReader in) throws IOException {
    JsonToken token = in.peek();
    switch (token) {
    case BEGIN_ARRAY:
      List list = new ArrayList();
      in.beginArray();
      while (in.hasNext()) {
        list.add(read(in));
      }
      in.endArray();
      return list;

    case BEGIN_OBJECT:
      Map map = new LinkedTreeMap();
      in.beginObject();
      while (in.hasNext()) {
        map.put(in.nextName(), read(in));
      }
      in.endObject();
      return map;

    case STRING:
      return in.nextString();

    case NUMBER:
      return in.nextDouble();

    case BOOLEAN:
      return in.nextBoolean();

    case NULL:
      in.nextNull();
      return null;

    default:
      throw new IllegalStateException();
    }
  }

  @SuppressWarnings("unchecked")
  @Override public void write(JsonWriter out, Object value) throws IOException {
    if (value == null) {
      out.nullValue();
      return;
    }

    TypeAdapter typeAdapter = (TypeAdapter) gson.getAdapter(value.getClass());
    if (typeAdapter instanceof ObjectTypeAdapter) {
      out.beginObject();
      out.endObject();
      return;
    }

    typeAdapter.write(out, value);
  }
}

 
  

查看read方法发现所有的Number类型都被转成了double类型,想要修改掉这个问题,需要自己实现一个TypeAdapter,处理Number类型的问题,自己重写TypeAdapter,代码如下:


public class DataTypeAdapter extends TypeAdapter {
    private final TypeAdapter delegate = new Gson().getAdapter(Object.class);

    @Override
    public Object read(JsonReader in) throws IOException {
        JsonToken token = in.peek();
        switch (token) {
            case BEGIN_ARRAY:
                List list = new ArrayList<>();
                in.beginArray();
                while (in.hasNext()) {
                    list.add(read(in));
                }
                in.endArray();
                return list;

            case BEGIN_OBJECT:
                Map map = new LinkedTreeMap<>();
                in.beginObject();
                while (in.hasNext()) {
                    map.put(in.nextName(), read(in));
                }
                in.endObject();
                return map;

            case STRING:
                return in.nextString();

            case NUMBER:
                /**
                 * 改写数字的处理逻辑,将数字值分为整型与浮点型。
                 */
                double dbNum = in.nextDouble();

                // 数字超过long的最大值,返回浮点类型
                if (dbNum > Long.MAX_VALUE) {
                    return dbNum;
                }
                // 判断数字是否为整数值
                long lngNum = (long) dbNum;
                if (dbNum == lngNum) {
                    try {
                        return (int) lngNum;
                    } catch (Exception e) {
                        return lngNum;
                    }
                } else {
                    return dbNum;
                }

            case BOOLEAN:
                return in.nextBoolean();

            case NULL:
                in.nextNull();
                return null;

            default:
                throw new IllegalStateException();
        }
    }

    @Override
    public void write(JsonWriter out, Object value) throws IOException {
        delegate.write(out, value);
    }
}
 
  

经过自己的处理将number类型都进行了转换,分别转为int、long和double,这样就可以解决int转为double的问题。
之后将自己重写的TypeAdapter注册一下

new GsonBuilder().registerTypeAdapter(new TypeToken>(){}.getType(),new DataTypeAdapter()).create();

这样使用返回的Gson对象进行转换就不会出现上述的问题。

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