当JSON使用日期作为属性名时，如何使用GSON将JSON反序列化为Java对象？

Question

我有一个JSON响应，我想使用GSON反序列化它。JSON结构使用日期字符串作为属性名。人们将如何进行反序列化这样的。

{
  2015-04-23: [{
     seqNum: 1,
     distance: 13,
     start: "123 Main St"
     end: "225 Broadway"
     },
     {seqNum: 2
      distance: 21,
      start: "225 Broadway"
      end: "12 West St"
      }
   ]
}

Answer 1

在我的回答中，我认为您可以得到这样的JSON响应：

{
    "2015-04-23": [
        {
            "seqNum": 1,
            "distance": 13,
            "start": "123 Main St",
            "end": "225 Broadway"
        },
        {
            "seqNum": 2,
            "distance": 21,
            "start": "225 Broadway",
            "end": "12 West St"
        }
    ],

    "2015-04-24": [
            {
                "seqNum": 1,
                "distance": 13,
                "start": "123 Main St",
                "end": "225 Broadway"
            },
            {
                "seqNum": 2,
                "distance": 21,
                "start": "225 Broadway",
                "end": "12 West St"
            }
        ]
}

因此，第一步是创建适当的类。

class MyObject {
    private List<DateMapping> dateMappings;

    public MyObject(List<DateMapping> dateMappings) {
        this.dateMappings = dateMappings;
    }
    ...
}
class DateMapping {
    private Date date;
    private List<Sequence> sequences;

    public DateMapping(Date date, List<Sequence> sequences) {
        this.date = date;
        this.sequences = sequences;
    }
    ...
}

class Sequence {
    private int seqNum;
    private int distance;
    private String start;
    private String end;
    ...
}

现在，如何解析这些键，因为它们是动态的？答案是使用自定义反序列化器：

class MyObjectAdapter implements JsonDeserializer<MyObject> {

    private static final SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
    private static final Type listSequenceType = new TypeToken<List<Sequence>>(){}.getType();

    public MyObject deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        List<DateMapping> dateMappings = new ArrayList<>();
        for(Map.Entry<String, JsonElement> entry : json.getAsJsonObject().entrySet()) {
            try {
                dateMappings.add(new DateMapping(dateFormat.parse(entry.getKey()), context.deserialize(entry.getValue(), listSequenceType)));
            } catch (ParseException e) {
                e.printStackTrace();
                throw new RuntimeException("Can't parse the date");
            }
        }
        return new MyObject(dateMappings);
    }
}

从这里可以看到，我迭代了顶级JsonObject的每个条目，您可以从这些条目中为每个条目创建一个新的DateMapping。然后，您只需在Gson解析器中注册适配器就可以了。

Gson gson = new GsonBuilder().registerTypeAdapter(MyObject.class, new MyObjectAdapter()).create();
MyObject myObject = gson.fromJson(new FileReader(new File("myJson")), MyObject.class);

在上面的示例上运行会产生输出：

MyObject => 
DateMapping Thu Apr 23 00:00:00 CEST 2015, sequences=[Sequence{seqNum=1, distance=13, start='123 Main St', end='225 Broadway'}, Sequence{seqNum=2, distance=21, start='225 Broadway', end='12 West St'}]
DateMapping Fri Apr 24 00:00:00 CEST 2015, sequences=[Sequence{seqNum=1, distance=13, start='123 Main St', end='225 Broadway'}, Sequence{seqNum=2, distance=21, start='225 Broadway', end='12 West St'}]

如果只有一个条目，则可以跳过类MyObject的创建，获得创建单个DateMapping实例的JsonObject的第一个条目。

希望能有所帮助！)