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。这将通过查看 Json 文件来更好地了解对象的结构。我尝试了Gson和org.codehaus.jackson.map.ObjectMapper库。但是无法生成与java pojo对象中的所有字段相关的所有Json标签。创建的 json 文件仅包含值 stetted 对象的值。我需要在 Json 文件中拥有 pojo 对象的所有字段。

格森

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);
}
}

杰伦

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

Answer 1

在GsonBuilder()上添加serializeNulls()以序列化空字段

配置 Gson 以序列化空字段。默认情况下，Gson 省略所有空字段 * 在序列化期间。

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
}

格森

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
}
]
}

Answer 2

您可以使用jackson-databind库。 Maven 依赖关系是：

<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.9.10</version>
</dependency>

另外，请在下面找到一些示例示例。在这里，我使用了员工对象，其中包含嵌套的地址对象。

员工.java

public class Employee {
private int empId;
private String firstName;
private String lastName;
private double salary;
private Address address;
public Employee() {}
public Employee(int empId, String firstName, String lastName, double salary) {
this.empId = empId;
this.firstName = firstName;
this.lastName = lastName;
this.salary = salary;
}
public Employee(int empId, String firstName, String lastName, double salary, Address address) {
this.empId = empId;
this.firstName = firstName;
this.lastName = lastName;
this.salary = salary;
this.address = address;
}
public int getEmpId() {
return empId;
}
public void setEmpId(int empId) {
this.empId = empId;
}
public String getFirstName() {
return firstName;
}
public void setFirstName(String firstName) {
this.firstName = firstName;
}
public String getLastName() {
return lastName;
}
public void setLastName(String lastName) {
this.lastName = lastName;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
}

地址.java

public class Address {
private String street;
private String city;
private String state;
private String zip;
private String country;
public Address() {}
public Address(String street, String city, String state, String zip, String country) {
this.street = street;
this.city = city;
this.state = state;
this.zip = zip;
this.country = country;
}
public String getStreet() {
return street;
}
public void setStreet(String street) {
this.street = street;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public String getState() {
return state;
}
public void setState(String state) {
this.state = state;
}
public String getZip() {
return zip;
}
public void setZip(String zip) {
this.zip = zip;
}
public String getCountry() {
return country;
}
public void setCountry(String country) {
this.country = country;
}
}

我将一个示例java pojo类转换为Json，并将JSON转换为pojo对象。

杰克逊转换.java

public class JacksonConvertion {
public static void main(String[] args) {
pojoToJson();
jsonToPojo();
}
private static void pojoToJson() {
try {
System.out.println("Convert Object to json ");
ObjectMapper mapper = new ObjectMapper();
Address address = new Address("#103, 1st cross, manyta tech park", "Bengaluru", "Karnataka", "560010",
"India");
Address address1 = new Address();
address1.setCity("Bengaluru");
address1.setState("Karnataka");
address1.setCountry("India");
Employee emp = new Employee(1233, "Raju", "BG", 98734.23, address1);
mapper.writeValue(new File("staff.json"), emp);
String jsonString = mapper.writeValueAsString(emp);
System.out.println(jsonString);
} catch (JsonProcessingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
private static void jsonToPojo() {
try {
System.out.println("Convert Json to Object ");
ObjectMapper mapper = new ObjectMapper();
Employee employee = mapper.readValue(new File("staff.json"), Employee.class);
System.out.println(employee.getFirstName());
System.out.println(employee.getSalary());
System.out.println(employee.getAddress().getCity());
} catch (IOException e) {
e.printStackTrace();
}
}
}

还包括一些链接供您参考。
链接1

链接2

Answer 3

我认为这会很好用

将 http://www.java2s.com/Code/Jar/c/Downloadcomfasterxmljacksondatabindjar.htm 和 http://www.java2s.com/Code/Jar/j/Downloadjacksondatabind205sourcesjar.htm 添加到您的库中。

import com.fasterxml.jackson.core.JsonProcessingException;

import com.fasterxml.jackson.databind.ObjectMapper;

public class javaPojo {

public static void main(String args[]){
Hotel hotel = new Hotel();
ObjectMapper mapper = new ObjectMapper();
try {
String json = mapper.writeValueAsString(hotel);
System.out.println("JSON = " + json);
} catch (JsonProcessingException e) {
e.printStackTrace();
}}

}

旅馆

import java.util.ArrayList;

import java.util.List;

公共类酒店 {

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);
}

}

房间

公共课室{

}

房价限制

公共类 RoomRateRestriction {

}

输出 - JSON = {"酒店代码"：空，"链码"：空，"酒店名称"：空，"房间"：[]，"房间价格限制"：[]}