Gson转换错误导致Int变为Double类型

浅浅的花香味﹌ 2024-04-07 14:50 77阅读 0赞

## 情况说明 ##

### 需要解析的json ###

{
        
        "status": 200,
        "msg": "OK",
        "data": [
            {
        
                "id": 1,
                "username": "eric",
                "password": "123456",
                "age": 29,
                "sex": 0,
                "permission": 0,
                "isDel": 0
            }
        ]
    }

### 类的定义 ###

@Data
    public class ResponseData implements Serializable {
        
        // 响应业务状态
        private Integer status;
        // 响应消息
        private String msg;
        // 响应中的数据
        private Object data;
    }

### 解析后 ###

ResponseData(status=200, msg=OK, data=[{id=1.0, username=eric, password=123456, age=29.0, sex=0.0, permission=0.0, isDel=0.0}])

进行处理后，变为

{
        
        "status": 200,
        "msg": "OK",
        "data": [
            {
        
                "id": 1.0,
                "username": "eric",
                "password": "123456",
                "age": 29.0,
                "sex": 0.0,
                "permission": 0.0,
                "isDel": 0.0
            }
        ]
    }

### 问题分析 ###

Object最后默认的TypeAdapter使用的是com.google.gson.internal.bind包下的ObjectTypeAdapter，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

## 解决 ##

上面我们分析后，是需要去重写TypeAdapter方法，在重写的这个方法里面，我们需要将其写出为对应的方法

### 第一步：重写TypeAdapter方法 ###

public class ResponseDataTypeAdaptor extends TypeAdapter<ResponseData> {
        
        public static final TypeAdapterFactory FACTORY = new TypeAdapterFactory() {
        
            @SuppressWarnings("unchecked")
            @Override
            public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> type) {
        
                if (type.getRawType() == ResponseData.class) {
        
                    return (TypeAdapter<T>) new ResponseDataTypeAdaptor(gson);
                }
                return null;
            }
        };
        private final Gson gson;
    
        ResponseDataTypeAdaptor(Gson gson) {
        
            this.gson = gson;
        }
    
        @Override
        public void write(JsonWriter out, ResponseData value) throws IOException {
        
            if (value == null) {
        
                out.nullValue();
                return;
            }
            out.beginObject();
            out.name("status");
            gson.getAdapter(Integer.class).write(out, value.getStatus());
            out.name("msg");
            gson.getAdapter(String.class).write(out, value.getMsg());
            out.name("data");
            gson.getAdapter(Object.class).write(out, value.getData());
            out.endObject();
        }
    
        @Override
        public ResponseData read(JsonReader in) throws IOException {
        
            ResponseData data = new ResponseData();
            Map<String, Object> dataMap = (Map<String, Object>) readInternal(in);
            data.setStatus((Integer) dataMap.get("status"));
            data.setMsg((String) dataMap.get("msg"));
            data.setData(dataMap.get("data"));
            return data;
        }
    
        private Object readInternal(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(readInternal(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(), readInternal(in));
                    }
                    in.endObject();
                    return map;
                case STRING:
                    return in.nextString();
                case NUMBER:
                    String numberStr = in.nextString();
                    if (numberStr.contains(".") || numberStr.contains("e") || numberStr.contains("E")) {
        
                        return Double.parseDouble(numberStr);
                    }
                    if (Long.parseLong(numberStr) <= Integer.MAX_VALUE) {
        
                        return Integer.parseInt(numberStr);
                    }
                    return Long.parseLong(numberStr);
                case BOOLEAN:
                    return in.nextBoolean();
                case NULL:
                    in.nextNull();
                    return null;
                default:
                    throw new IllegalStateException();
            }
        }
    }

### 第二步：注册gson ###

将自己重写的TypeAdapter注册一下

private static Gson buildGson() {
        
        GsonBuilder gsonBuilder = new GsonBuilder();
        gsonBuilder.registerTypeAdapterFactory(DataTypeAdaptor.FACTORY);
        return gsonBuilder.create();
    
    }

### 第三步：测试 ###

public class GsonTest {
        
        public static void main(String[] args) {
        
            String dataJson = "{\"status\":200,\"msg\":\"OK\",\"data\":[{\"id\":1,\"username\":\"eric\",\"password\":\"123456\",\"age\":29,\"sex\":0,\"permission\":0,\"isDel\":0}]}";
            Gson gson = buildGson();
            ResponseData data = gson.fromJson(dataJson, ResponseData.class);
            System.out.println(data.toString());
        }
    }

## 其他问题 ##

解析过程中，还会出现转换问题，如：  
`com.google.gson.internal.LinkedTreeMap cannot be cast to XXX`

### 问题1：LinkedTreeMap cannot be cast to XXX ###

这种情况出现的原因是：  
`进行到对list进行操作的那步，报错了（java.lang.ClassCastException: com.google.gson.internal.LinkedTreeMap cannot be cast to xx）。原来list中的数据是LinkedTreeMap 格式的，并没有转换成对应的实体类。`

那么现在就需要自己去改写一下之前所重写的TypeAdapter方法

### 问题1：解决 ###

去遍历这个LinkedTreeMap 这个Map

LinkedTreeMap,可通过key来获取value的map

如下去一步一步遍历，将遍历的结果设置到对应的实体类中

LinkedTreeMap tm = (LinkedTreeMap)fromJson2;
    Iterator it = tm.keySet().iterator();  
    while (it.hasNext()) {
          
        String key = (String) it.next();
        String value = (String)tm.get(key);
    }