使用 Jackson 在同一文件中使用未知键名处理多个 JSON 对象

Question

正在为处理实体建筑的应用程序构建模型。

理想情况下，我们想要这样的东西：

城市有多个办公室，办公室有多个房间，房间有属性。

我们正在使用 jackson 来解析从 API 数据源接收到的 JSON 有效负载，它最终看起来与我看到的示例有点不同。

我们得到的格式是：

{
"CityName1": 
    { "OfficeName1": 
        [   
            {"name": RoomName1, "RoomProperty2": RoomValue1},
            {"name": RoomName2, "RoomProperty2": RoomValue2}
        ]
    }, 
    { "OfficeName2": [{...}]},
    { "OfficeNameX" : [{...}] },
"CityName2": {...},
"CityNameN": {...}}

Java classes:

public class City {
  private Map<String, Object> additionalProperties = new HashMap<String, Object();

  private List<Office> _offices = new ArrayList<Office>();

  @JsonAnyGetter
  public Map<String, Object> getAdditionalProperties() {
    return this.additionalProperties;
  }

  @JsonAnySetter
  public void setAdditionalProperty(String name, Object value)
      throws IOException {
    _cityName = name;
    String officeJson = _mapper.writeValueAsString(value);
    StringBuilder sb = new StringBuilder(officeJson);
    _offices.add(_mapper.readValue(officeJson, Office.class));
    this.additionalProperties.put(name, value);
  }
}

public class Office {

  private String _officeName;

  private static final ObjectMapper _mapper = new ObjectMapper();

  private Map<String, Object> additionalProperties = new HashMap<String, Object>();

  private List<Room> _rooms = new ArrayList<Room>();

  @JsonAnyGetter
  public Map<String, Object> getAdditionalProperties() {
    return this.additionalProperties;
  }

  @JsonAnySetter
  public void setAdditionalProperty(String name, Object value)
      throws IOException {
    _officeName = name;
    String roomJson = _mapper.writeValueAsString(value);
    Room[] rooms  = _mapper.readValue(roomJson, Room[].class);
    _rooms.addAll(Arrays.asList(rooms));
    this.additionalProperties.put(name, value);
  }

  public List<Room> getRooms() {
    return _rooms;
  }

  public void setRooms(List<Room> rooms) {
    _rooms = rooms;
  }  
}

public class Room {

  private static final String NAME = "name";
  private static final String PROP_2 = "RoomProperty2";

  @JsonProperty(PROP_2)
  private String _propertyTwo;

  @JsonProperty(NAME)
  private String name;

  @JsonProperty(PROP_2)
  public String getPropertyTwo() {
    return _propertyTwo;
  }

  @JsonProperty(PROP_2)
  public void setPropertyTwo(String propTwo) {
    _propertyTwo = propTwo;
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

那么我将如何用 jackson 解析它？目前，我正在使用 @JsonAnySetter 获取名称，并将其保存为城市或办公室名称，然后将发送到 JsonAnySetter 的值发送到适当的嵌套 class。真正的问题在于获取城市中的办公室列表。当使用 mapper.readvalues(String, Office.class) 时，我得到了每个城市的最后一个办公室的迭代器。有什么想法吗？

抱歉，如果这看起来令人困惑！很乐意回答我提出的任何问题。

感谢您的帮助！

Answer 1

我认为最好的解决方案是在此处编写您自己的 deserialiser，因为您的 JSON 文档并不能很好地映射到您想要的 class 结构。

下面的解决方案将每个城市读取为 Map<String, List<Room>>，将城市集合读取为 Map<String, City>，然后在反序列化器中从这些对象中创建 City 和 Office 对象.

Room.java和你的一样，下面是：

Cities.java:

@JsonDeserialize(using=CitiesDeserializer.class)
public class Cities implements Iterable<City> {

    private final List<City> cities;

    public Cities(final List<City> cities) {
        this.cities = cities;
    }

    public Cities() {
        this.cities = new ArrayList<>();
    }

    public List<City> getCities() {
        return cities;
    }

    @Override
    public Iterator<City> iterator() {
        return cities.iterator();
    }
}

CitiesDeserialiser.java:

public class CitiesDeserializer extends JsonDeserializer<Cities> {
    private static final TypeReference<Map<String, City>> TYPE_REFERENCE = new TypeReference<Map<String, City>>() {};

    @Override
    public Cities deserialize(final JsonParser jp, final DeserializationContext ctxt) throws IOException {
        final Map<String, City> map = jp.readValueAs(TYPE_REFERENCE);
        List<City> cities = new ArrayList<>();
        for(Map.Entry<String, City> entry : map.entrySet()) {
            City city = entry.getValue();
            city.setName(entry.getKey());
            cities.add(city);
        }
        return new Cities(cities);
    }
}

City.java:

@JsonDeserialize(using=CityDeserialzer.class)
public class City {

    private String name;

    private List<Office> offices;

    // Setters and getters
}

CityDeserializer.java:

public class CityDeserialzer extends JsonDeserializer<City> {
    private static final TypeReference<Map<String, List<Room>>> TYPE_REFERENCE = new TypeReference<Map<String, List<Room>>>() {};

    @Override
    public City deserialize(final JsonParser jp, final DeserializationContext ctxt) throws IOException {
        final Map<String, List<Room>> map = jp.readValueAs(TYPE_REFERENCE);
        List<Office> offices = new ArrayList<>();
        for(Map.Entry<String, List<Room>> entry : map.entrySet()) {
            Office office = new Office();
            office.setName(entry.getKey());
            office.setRooms(entry.getValue());
            offices.add(office);
        }
        City city = new City();
        city.setOffices(offices);
        return city;
    }
}

Office.java:

public class Office {

    private String name;

    private List<Room> rooms;

    // Setters and getters
}

这是一个证明它有效的测试：

JSON:

{
    "CityName1": {
        "OfficeName1": [ {
                "name": "RoomName1",
                "RoomProperty2": "RoomValue1"
            }, {
                "name": "RoomName2",
                "RoomProperty2": "RoomValue2"
            } ],
        "OfficeName2": [ {
                "name": "RoomName3",
                "RoomProperty2": "RoomValue3"
            }, {
                "name": "RoomName4",
                "RoomProperty2": "RoomValue4"
            } ]
    },
    "CityName2": {
        "OfficeName3": [ {
                "name": "RoomName5",
                "RoomProperty2": "RoomValue5"
            }, {
                "name": "RoomName6",
                "RoomProperty2": "RoomValue6"
            } ],
        "OfficeName4": [ {
                "name": "RoomName7",
                "RoomProperty2": "RoomValue7"
            }, {
                "name": "RoomName8",
                "RoomProperty2": "RoomValue8"
            } ]
    }
}

Test.java:

public class Test {

    public static void main(String[] args) {
        String json = ...
        ObjectMapper mapper = new ObjectMapper();
        Cities cities = mapper.readValue(json, Cities.class);
        for(City city : cities) {
            System.out.println(city.getName());
            for(Office office : city.getOffices()) {
                System.out.println("\t" + office.getName());
                for(Room room : office.getRooms()) {
                    System.out.println("\t\t" + room.getName());
                    System.out.println("\t\t\t" + room.getPropertyTwo());
                }
            }
        }
    }
}

输出：

CityName1
    OfficeName1
        RoomName1
            RoomValue1
        RoomName2
            RoomValue2
    OfficeName2
        RoomName3
            RoomValue3
        RoomName4
            RoomValue4
CityName2
    OfficeName3
        RoomName5
            RoomValue5
        RoomName6
            RoomValue6
    OfficeName4
        RoomName7
            RoomValue7
        RoomName8
            RoomValue8

使用 Jackson 在同一文件中使用未知键名处理多个 JSON 对象

Working with multiple JSON objects in the same file with unknown key names using Jackson

java

json

jackson

fasterxml