Object Mapper

dependency 찾는 법 -> https://mvnrepository.com/search?q=object+mapper

maven Repository 가서 사용할 것 찾음

온라인에서 라이브러리 찾아서 자동으로 추가

dependencies {
    // https://mvnrepository.com/artifact/com.fasterxml.jackson.core/jackson-databind
    implementation group: 'com.fasterxml.jackson.core', name: 'jackson-databind', version: '2.12.1'
    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.8.1'
    testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.8.1'
}

{
  "name": "홍길동",
  "age": 10,
  "cars": [
    {
      "name": "K5",
      "carNumber": "11가 1111",
      "type": "sedan"
    },
    {
      "name": "Q5",
      "carNumber": "22가 2222",
      "type": "SUV"
    }
  ]
}

package dto;

import com.fasterxml.jackson.annotation.JsonProperty;

public class Car {
    private String name;
    
    @JsonProperty("car_number")
    private String carNumber;
    
    @JsonProperty("TYPE")
    private String type;

    public String getName() {
        return name;
    }

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

    public String getCarNumber() {
        return carNumber;
    }

    public void setCarNumber(String carNumber) {
        this.carNumber = carNumber;
    }

    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    @Override
    public String toString() {
        return "Car{" +
                "name='" + name + '\'' +
                ", carNumber='" + carNumber + '\'' +
                ", type='" + type + '\'' +
                '}';
    }
}

package dto;

import java.util.List;

public class User {

    private String name;
    private int age;

    private List<Car> cars;

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public List<Car> getCars() {
        return cars;
    }

    public void setCars(List<Car> cars) {
        this.cars = cars;
    }

    @Override
    public String toString() {
        return "User{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", cars=" + cars +
                '}';
    }
}

package org.example;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.node.ArrayNode;
import com.fasterxml.jackson.databind.node.ObjectNode;
import dto.Car;
import dto.User;

import java.util.Arrays;
import java.util.List;

public class Main {
    public static void main(String[] args) throws JsonProcessingException {
        System.out.println("main");

        // 맥은 디폴트가 UTF-8이라 에러가 안나지만 윈도우는 남
        ObjectMapper objectMapper = new ObjectMapper();

        User user = new User();
        user.setName("홍길동");
        user.setAge(10);

        Car car1 = new Car();
        car1.setName("K5");
        car1.setCarNumber("11가 1111");
        car1.setType("sedan");

        Car car2 = new Car();
        car2.setName("Q5");
        car2.setCarNumber("22가 2222");
        car2.setType("SUV");

        List<Car> carList = Arrays.asList(car1, car2);
        user.setCars(carList);

        System.out.println(user);

        String json = objectMapper.writeValueAsString(user);
        System.out.println(json);

        //순수 노드에 접근하는 법
        JsonNode jsonNode = objectMapper.readTree(json);
        // 파싱
        String _name = jsonNode.get("name").asText();
        int _age = jsonNode.get("age").asInt();

        System.out.println("name :" + _name);
        System.out.println("age :" + _age);

        // 아무 것도 안 찍힘
//        String _list = jsonNode.get("cars").asText();
//        System.out.println(_list);

        //cars는 일종의 노드
        JsonNode cars = jsonNode.get("cars");
        ArrayNode arrayNode = (ArrayNode)cars;

        List<Car> _cars = objectMapper.convertValue(arrayNode, new TypeReference<List<Car>>() {});
        System.out.println(_cars);

        // JSONNODE 값 바꾸는법 put을 통해 벨류 값 바꾸었음
        ObjectNode objectNode = (ObjectNode) jsonNode;
        objectNode.put("name", "steve");
        objectNode.put("age", 20);

        System.out.println(objectNode.toPrettyString());
    }
}

어노테이션(Annotation) 정리