Gson conversion causes int to double

When we use Object or Map generics, when we convert json, we find that all values in the data are double and 0 is 0.0, which may cause some problems in subsequent programs.

Check Gson source code, find the Object the default TypeAdapter using com. Google. Gson. Internal. Bind ObjectTypeAdapter under the package, inside process is as follows:

/** * 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<Object> {
  public static final TypeAdapterFactory FACTORY = new TypeAdapterFactory() {
    @SuppressWarnings("unchecked")
    @Override public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
      if (type.getRawType() == Object.class) {
        return (TypeAdapter<T>) 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<Object> list = new ArrayList<Object>();
      in.beginArray();
      while (in.hasNext()) {
        list.add(read(in));
      }
      in.endArray();
      return list;

    case BEGIN_OBJECT:
      Map<String, Object> map = new LinkedTreeMap<String, Object>();
      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 newIllegalStateException(); }}@SuppressWarnings("unchecked")
  @Override public void write(JsonWriter out, Object value) throws IOException {
    if (value == null) {
      out.nullValue();
      return;
    }

    TypeAdapter<Object> typeAdapter = (TypeAdapter<Object>) gson.getAdapter(value.getClass());
    if (typeAdapter instanceof ObjectTypeAdapter) {
      out.beginObject();
      out.endObject();
      return; } typeAdapter.write(out, value); }}Copy the code

TypeAdapter (double); TypeAdapter (double); TypeAdapter (double);

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

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

            case BEGIN_OBJECT:
                Map<String, Object> 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:
                /** * Rewrites the numeric processing logic to divide numeric values into integer and floating point types. * /
                double dbNum = in.nextDouble();

                // If the number exceeds the maximum value of long, return a floating-point type
                if (dbNum > Long.MAX_VALUE) {
                    return dbNum;
                }
                // Check whether the number is an integer value
                long lngNum = (long) dbNum;
                if (dbNum == lngNum) {
                    try {
                        return (int) lngNum;
                    } catch (Exception e) {
                        returnlngNum; }}else {
                    return dbNum;
                }

            case BOOLEAN:
                return in.nextBoolean();

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

            default:
                throw newIllegalStateException(); }}@Override
    public void write(JsonWriter out, Object value) throws IOException { delegate.write(out, value); }}Copy the code

The number type is converted to int, long, and double, respectively. Then register the TypeAdapter you have overwritten

new GsonBuilder().registerTypeAdapter(new TypeToken<Map<String,Object>>(){}.getType(),new DataTypeAdapter()).create();
Copy the code

In this way, the conversion using the returned Gson object does not have the problem described above.