java - 从一组 Java Pojo 类创建 JSON 结构

Question

我需要从一组 java pojo 类创建一个 JSON 对象结构。只需查看 Json 文件，就可以更好地理解对象的结构。我尝试了 Gson 和 org.codehaus.jackson.map.ObjectMapper 库。但无法生成与 java pojo 对象中所有字段相关的所有 Json 标签。创建的 json 文件仅包含来自值设置对象的值。我需要在 Json 文件中包含 pojo 对象的所有字段。

Gson

        Hotel hotel = new Hotel(); //This hotel object includes multiple objects and those objects also include multiple objects, lists
        Gson gson = new GsonBuilder().create();
        String json = gson.toJson(hotel);
        System.out.println(json);

对象映射器

ObjectMapper mapper = new ObjectMapper();
mapper.writeValue(new File("/home/Pojos.json");

这是我得到的类和 json 响应。

酒店.java

package datatypes;

import java.util.ArrayList;
import java.util.List;

public class Hotel {


    private     String      hotelCode;
    private     String      chainCode;
    private     String      hotelName;
    private     List<Room>  rooms           =   new ArrayList<Room>(); 
    private     List<RoomRateRestriction>   roomRateRestrictions
    =   new ArrayList<RoomRateRestriction>();


    public String getHotelCode() {
        return hotelCode;
    }
    public void setHotelCode(String hotelCode) {
        this.hotelCode = hotelCode;
    }
    public String getChainCode() {
        return chainCode;
    }
    public void setChainCode(String chainCode) {
        this.chainCode = chainCode;
    }
    public String getHotelName() {
        return hotelName;
    }
    public void setHotelName(String hotelName) {
        this.hotelName = hotelName;
    }
    public List<Room> getRooms() {
        return rooms;
    }
    public void setRooms(List<Room> rooms) {
        this.rooms = rooms;
    }

    public void addRoom(Room room){
        this.rooms.add(room);
    }
    public List<RoomRateRestriction> getRoomRateRestrictions() {
        return roomRateRestrictions;
    }
    public void setRoomRateRestrictions(
            List<RoomRateRestriction> roomRateRestrictions) {
        this.roomRateRestrictions = roomRateRestrictions;
    }

    public void addRoomRateRestrictions(
            RoomRateRestriction roomRateRestriction) {
        this.roomRateRestrictions.add(roomRateRestriction);
    }
}

JSON

   {
     "rooms":[],
     "roomRateRestrictions":[]
   }

Answer 1

在 GsonBuilder() 上添加 serializeNulls() 以序列化 null 字段

Configure Gson to serialize null fields. By default, Gson omits all fields that are null * during serialization.

class Hotel {
    private String name;
    private List<Guest> guests = new ArrayList<>(Collections.singleton(new Guest())); //you have to set a value in order to get the structure of the Guest class otherwise it will show an empty list []
    //getter setter
}

class Guest {
   private String name;
   //getter setter
}

Gson

 Hotel hotel = new Hotel();
 Gson gson = new GsonBuilder().serializeNulls().create();
 String json = gson.toJson(hotel);
 System.out.println(json);

输出

{  
 "name":null, 
 "guests":[  
      {  
         "name":null
      }
   ]
}