<!-- https://mvnrepository.com/artifact/com.google.code.gson/gson -->
<dependency>
    <groupId>com.google.code.gson</groupId>
    <artifactId>gson</artifactId>
    <version>2.14.0</version>
</dependency>

Gson gson = new Gson();
String jsonText = gson.toJson(someInstance, SomeType.class);

Gson gson = new Gson();
SomeType someInstance = gson.fromJson(jsonText, SomeType.class);

package org.jadv.model;

import com.google.gson.annotations.JsonAdapter;
import lombok.Getter;
import org.jadv.serialization.SavedObjectAdapter;

/**
 * An instance that can be saved through an Adapter and contains the name of the class as field.
 */
@JsonAdapter(SavedObjectAdapter.class)
public abstract class SavedObject {
    /**
     * Class name of the
     */
    @Getter
    private final String type = getClass().getName();
}

    /**
     * Serializes an SavedObject to JSON. Makes sure that the serialization is using the correct class.
     * @param object Object to serialize.
     * @param interfaceType Not used.
     * @param context Serialization context.
     * @return The JsonElement that holds the serialized object.
     */
    @Override
    public JsonElement serialize(SavedObject object, Type interfaceType, JsonSerializationContext context) {
        if (object == null) return null;
        return context.serialize(object, object.getClass());
    }

    /**
     * Deserializes the SavedInstance from a json.
     * @param elem Json element to deserialize
     * @param interfaceType not used.
     * @param context Deserialization context.
     * @return The restored instance with correct class.
     * @throws JsonParseException Throws an JsonParseException if deserialization is not possible.
     */
    @Override
    public SavedObject deserialize(JsonElement elem, Type interfaceType, JsonDeserializationContext context) throws JsonParseException {
        final JsonObject wrapper = (JsonObject) elem;
        final JsonElement typeName = get(wrapper, "type");
        final Type actualType = typeForName(typeName);
        return context.deserialize(elem, actualType);
    }

package org.jadv.serialization;

import com.google.gson.*;
import org.jadv.model.SavedObject;

import java.lang.reflect.Type;

/**
 * Gson Adapter to (de-)serialize derived types.
 */
final public class SavedObjectAdapter implements JsonSerializer<SavedObject>, JsonDeserializer<SavedObject> {
    /**
     * Serializes an SavedObject to JSON. Makes sure that the serialization is using the correct class.
     * @param object Object to serialize.
     * @param interfaceType Not used.
     * @param context Serialization context.
     * @return The JsonElement that holds the serialized object.
     */
    @Override
    public JsonElement serialize(SavedObject object, Type interfaceType, JsonSerializationContext context) {
        if (object == null) return null;
        return context.serialize(object, object.getClass());
    }

    /**
     * Deserializes the SavedInstance from a json.
     * @param elem Json element to deserialize
     * @param interfaceType not used.
     * @param context Deserialization context.
     * @return The restored instance with correct class.
     * @throws JsonParseException Throws an JsonParseException if deserialization is not possible.
     */
    @Override
    public SavedObject deserialize(JsonElement elem, Type interfaceType, JsonDeserializationContext context) throws JsonParseException {
        final JsonObject wrapper = (JsonObject) elem;
        final JsonElement typeName = get(wrapper, "type");
        final Type actualType = typeForName(typeName);
        return context.deserialize(elem, actualType);
    }

    /**
     * Gets the type for a given name.
     * @param typeElem JsonElement with classname inside.
     * @return The requested class.
     * @throws JsonParseException Thrown if the class is not available / known.
     */
    private Type typeForName(final JsonElement typeElem) throws JsonParseException {
        try {
            return Class.forName(typeElem.getAsString());
        } catch (ClassNotFoundException e) {
            throw new JsonParseException(e);
        }
    }

    /**
     * Gets an child element of an JsonObject,
     * @param wrapper Wrapper JsonObject to get the element from.
     * @param memberName Name of the element to get.
     * @return The requested JsonElement.
     * @throws JsonParseException Thrown if the requested element is not available.
     */
    private JsonElement get(final JsonObject wrapper, String memberName) throws JsonParseException {
        final JsonElement elem = wrapper.get(memberName);
        if (elem == null) throw new JsonParseException("no '" + memberName + "' member found in what was expected to be an interface wrapper");
        return elem;
    }
}

package org.jadv.serialization;

import com.google.gson.*;
import org.jadv.model.SavedObject;

import java.lang.reflect.Type;
import java.util.ArrayList;
import java.util.List;

/**
 * Gson Adapter to (de-)serialize derived types.
 */
final public class ListOfSavedObjectAdapter implements JsonSerializer<List<SavedObject>>, JsonDeserializer<List<SavedObject>> {
    /**
     * Serializes a list of SavedInstance to JSON.
     * @param list Object to serialize.
     * @param interfaceType Not used.
     * @param context Serialization context.
     * @return The JsonElement that holds the serialized list.
     */
    public JsonElement serialize(List<SavedObject> list, Type interfaceType, JsonSerializationContext context) {
        if (list == null) return null;
        final JsonArray array = new JsonArray();
        for (SavedObject obj : list) {
            array.add(context.serialize(obj, SavedObject.class));
        }
        return array;
    }

    /**
     * Deserializes the list of SavedInstance from a json.
     * @param elem Json element to deserialize
     * @param interfaceType not used.
     * @param context Deserialization context.
     * @return The restored list with elements with correct class.
     * @throws JsonParseException Throws an JsonParseException if deserialization is not possible.
     */
    public List<SavedObject> deserialize(JsonElement elem, Type interfaceType, JsonDeserializationContext context) throws JsonParseException {
        List<SavedObject> result = new ArrayList<>();
        final JsonArray array = (JsonArray) elem;
        for (JsonElement element : array.asList()) {
            result.add(context.deserialize(element, SavedObject.class));
        }
        return result;
    }
}