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<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 new IllegalStateException();
}
}
@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);
}
}
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<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:
/**
* 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<Map<String,Object>>(){}.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。
