如何在json中正确序列化/反序列化具有复杂结构的类对象

这个问题很可能已经被问过了，但是我能找到的所有东西都有一点，但仍然不合适。问题的本质：在项目中，我需要能够从文件中保存和读取有关CollectionManager存储HashSet类对象Dragon和更多变量的类对象的数据。实际上，问题在于类对象Dragon还包含其他已经属于类DragonCave和Coordinates. 我需要以某种方式保存我编写/读取的 collectionManager 包含一组龙的信息，这些龙仍然有它们的洞穴和它们的坐标。

还有一个小问题：我在集合管理器和 Dragon 本身中有类型字段java.time.LocalDate，当我尝试使用 Gson 库对它们进行序列化时，抛出异常“无法使字段私有静态最终长 java. time.LocalDate.serialVersionUID 可访问：模块 java.base 不会“打开 java.time”到未命名模块 @6d86b085”

谢谢你花时间陪我。

类和解析器代码： CollectionManager：

package Managers;

import Classes.Dragon;
import Exceptions.FieldNullException;
import Exceptions.IncorrectFieldValueException;

import java.time.LocalDate;
import java.util.HashSet;
import java.util.StringJoiner;


public class CollectionManager {
    private long currentId = 0;
    private HashSet<Dragon> collection;
    private final LocalDate initializationDate;
    private String filePath;

    public CollectionManager(HashSet<Dragon> collection, String filePath) throws IncorrectFieldValueException, FieldNullException {
        this.filePath = filePath;
        this.collection = collection;
        initializationDate = getDate();
    }

    public void setFilePath(String filePath){
        this.filePath = filePath;
    }

    public long getNewId(){
        return currentId++;
    }

    public LocalDate getDate(){
        return LocalDate.now();
    }

    public HashSet<Dragon> getCollection(){
        return collection;
    }

    public void addElement(Dragon element){
        collection.add(element);
    }

    public void removeElementById(Long id){
        collection.removeIf(d -> d.getId().equals(id));
    }

    public void clear(){
        collection.clear();
    }

    public LocalDate getInitializationDate() {
        return initializationDate;
    }

    public String toString() {
        StringJoiner stringJoiner = new StringJoiner("\n");
        if (collection.size() > 0) {
            collection.forEach((k) -> stringJoiner.add(k.toString()));
        } else {
            stringJoiner.add("The collection is empty");
        }
        return stringJoiner.toString();
    }
}

龙：

package Classes;

import Managers.CollectionManager;
import Exceptions.FieldNullException;
import Exceptions.IncorrectFieldValueException;

import java.time.LocalDate;
import java.util.Objects;

public class Dragon implements Comparable<Dragon>{
    private Long id; //Поле не может быть null, Значение поля должно быть больше 0, Значение этого поля должно быть уникальным, Значение этого поля должно генерироваться автоматически
    private String name; //Поле не может быть null, Строка не может быть пустой
    private Coordinates coordinates; //Поле не может быть null
    private java.time.LocalDate creationDate; //Поле не может быть null, Значение этого поля должно генерироваться автоматически
    private int age; //Значение поля должно быть больше 0
    private float wingspan; //Значение поля должно быть больше 0
    private Boolean speaking; //Поле не может быть null
    private Color color; //Поле не может быть null
    private DragonCave cave; //Поле не может быть null


    public Dragon(CollectionManager collectionManager, String name, Coordinates coordinates, int age,
                  float wingspan, Boolean speaking, Color color, DragonCave cave)
            throws FieldNullException, IncorrectFieldValueException {
        if (collectionManager == null) {
            throw new FieldNullException("CollectionManager");
        } else if (name == null) {
            throw new FieldNullException("name");
        } else if (coordinates == null) {
            throw new FieldNullException("coordinates");
        } else if (speaking == null) {
            throw new FieldNullException("speaking");
        } else if (color == null) {
            throw new FieldNullException("color");
        } else if (cave == null) {
            throw new FieldNullException("cave");
        }

        if (name.equals("")) {
            throw new IncorrectFieldValueException("name", name, "not null and not \"\"");
        } else if (age <= 0) {
            throw new IncorrectFieldValueException("age", String.valueOf(age), "greater than 0");
        } else if (wingspan <= 0) {
            throw new IncorrectFieldValueException("wingspan", String.valueOf(wingspan), "greater than 0");
        }

        this.id = collectionManager.getNewId();
        this.name = name;
        this.coordinates = coordinates;
        this.creationDate = collectionManager.getDate();
        this.age = age;
        this.wingspan = wingspan;
        this.speaking = speaking;
        this.color = color;
        this.cave = cave;
    }


    // гетеры
    public Long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public Coordinates getCoordinates() {
        return coordinates;
    }

    public LocalDate getCreationDate() {
        return creationDate;
    }

    public int getAge() {
        return age;
    }

    public float getWingspan() {
        return wingspan;
    }

    public Boolean getSpeaking() {
        return speaking;
    }

    public Color getColor() {
        return color;
    }

    public DragonCave getCave() {
        return cave;
    }


    // сеттеры
    public void setId(Long id) {
        this.id = id;
    }

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

    public void setCoordinates(Coordinates coordinates) {
        this.coordinates = coordinates;
    }

    public void setCreationDate(LocalDate creationDate) {
        this.creationDate = creationDate;
    }

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

    public void setWingspan(float wingspan) {
        this.wingspan = wingspan;
    }

    public void setSpeaking(Boolean speaking) {
        this.speaking = speaking;
    }

    public void setColor(Color color) {
        this.color = color;
    }

    public void setCave(DragonCave cave) {
        this.cave = cave;
    }

    public int compareTo(Dragon anotherDragon){
        if (name.compareTo(anotherDragon.getName()) != 0) {
            return name.compareTo(anotherDragon.getName());
        }
        else if (Integer.valueOf(age).compareTo(anotherDragon.getAge()) != 0){
            return Integer.valueOf(age).compareTo(anotherDragon.getAge());
        }
        else{
            return Float.valueOf(wingspan).compareTo(anotherDragon.getWingspan());
        }
    }

    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Dragon dragon)) return false;
        return age == dragon.age && Float.compare(dragon.wingspan, wingspan) == 0 && id.equals(dragon.id) &&
                name.equals(dragon.name) && coordinates.equals(dragon.coordinates) &&
                creationDate.equals(dragon.creationDate) && speaking.equals(dragon.speaking) &&
                color == dragon.color && cave.equals(dragon.cave);
    }

    public int hashCode() {
        return Objects.hash(id, name, coordinates, creationDate, age, wingspan, speaking, color, cave);
    }

    public String toString() {
        return "Dragon{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", coordinates=" + coordinates +
                ", creationDate=" + creationDate +
                ", age=" + age +
                ", wingspan=" + wingspan +
                ", speaking=" + speaking +
                ", color=" + color +
                ", cave=" + cave +
                '}';
    }
}

坐标：

package Classes;

import Exceptions.IncorrectFieldValueException;

public class Coordinates {
    private long x; //Значение поля должно быть больше -846
    private double y;

    public Coordinates(long x, double y) throws IncorrectFieldValueException{
        setX(x);
        setY(y);
    }

    public double getY() {
        return y;
    }

    public void setY(double y) {
        this.y = y;
    }

    public long getX() {
        return x;
    }

    public void setX(long x) throws IncorrectFieldValueException {
        if (x < -845) throw new IncorrectFieldValueException("x", String.valueOf(x), "greater than -846");
        this.x = x;
    }

    @Override
    public String toString() {
        return "Coordinates{" +
                "x=" + x +
                ", y=" + y +
                '}';
    }
}

龙穴：

package Classes;

import java.util.Objects;

public class DragonCave {
    private int depth;

    public DragonCave(int depth){
        this.depth = depth;
    }

    public int getDepth() {
        return depth;
    }

    public void setDepth(int depth) {
        this.depth = depth;
    }

    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof DragonCave)) return false;
        DragonCave that = (DragonCave) o;
        return depth == that.depth;
    }

    public int hashCode() {
        return Objects.hash(depth);
    }

    public String toString() {
        return "DragonCave{" +
                "depth=" + depth +
                '}';
    }
}

颜色：

package Classes;

import java.util.Arrays;
import java.util.Map;
import java.util.stream.Collectors;

public enum Color {

    BLUE("синий"),
    YELLOW("жёлтый"),
    WHITE("белый");

    private final String colorName;

    private Color(String colorName) {
        this.colorName = colorName;
    }

    private final static Map<String, Color> colors = Arrays.stream(Color.values())
            .collect(Collectors.toMap(k->k.colorName, v->v));

    public static Color getColorByName(String colorName) {
        return colors.get(colorName);
    }

    public String toString() {
        return colorName;
    }
}

解析器：

package Managers;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.HashSet;
import java.util.Scanner;

import Exceptions.FieldNullException;
import Exceptions.IncorrectFieldValueException;
import com.google.gson.Gson;

public class Parser {
    private Parser() {
    }

    public static CollectionManager convertToJavaObject(File file) throws FieldNullException, IncorrectFieldValueException, FileNotFoundException {
        Gson gson = new Gson();
        // магическим образом получить строку(data) из всего этого
        Scanner scan = new Scanner(file);
        String data = scan.nextLine();
        // это просто отвратительно, но другого способа не придумал
        CollectionManager collectionManager = gson.fromJson(data, CollectionManager.class);
        collectionManager.setFilePath(file.getPath());
        return new CollectionManager(new HashSet<>(), "");
    }

    public static void convertToJSON(CollectionManager data){
        Gson gson = new Gson();
        String json = gson.toJson(data);
        System.out.println(json);
    }
}