how to serialize non featured data type?

[Sombian]

in Spigot's API, one create custom PersistentDataType to store almost anything, easily.

e.g.

abstract class NamedBinaryTag<T : Any, Z : Any> : PersistentDataType<T, Z> {
	abstract fun toPrimitive(complex: Z): T
	
	override fun toPrimitive(complex: Z, context: PersistentDataAdapterContext): T {
		return toPrimitive(complex)
	}
	abstract fun fromPrimitive(primitive: T): Z

	override fun fromPrimitive(primitive: T, context: PersistentDataAdapterContext): Z {
		return fromPrimitive(primitive)
	}
}
class _SERIALIZABLE<T : Serializable>(private val type: Class<T>) : NamedBinaryTag<ByteArray, T>() {
	override fun getPrimitiveType(): Class<ByteArray> {
		return ByteArray::class.java
	}
	override fun getComplexType(): Class<T> {
		return this.type
	}
	override fun toPrimitive(complex: T): ByteArray {
		val bos = ByteArrayOutputStream()
		val oos = ObjectOutputStream(bos)
		oos.writeObject(complex)
		oos.flush()
		return bos.toByteArray()
	}
	override fun fromPrimitive(primitive: ByteArray): T {
		val bis = ByteArrayInputStream(primitive)
		val ois = ObjectInputStream(bis)
		@Suppress("UNCHECKED_CAST")
		return ois.readObject() as T
	}
}

certainly, current Tag API provides extra types that are not present in Spigot's by default.
but Minestorm also dont provides some useful types like ByteArray that can be found in Spigot's.

im very new to Minestom, hence thats why im asking,
since there arent much tutorials or resources out there yet.

can i have some examples of how to achieve this?

[TheMode]

You can use Tag.NBT("name") for array support (and probably even cast the generic to be NBTByteArray). Or if you are fine with a list, Tag.Byte("name").list()

This is only in answer to your byte array question, feel free to ask if you wonder about another specific type

[Sombian]

does API support any type out of box?
and how does Tag.NBT("name") magically supports array?

    public static @NotNull Tag<NBT> NBT(@NotNull String key) {
        return tag(key, Serializers.NBT_ENTRY);
    }

i dont see any hard-coded string from the source code.

public class Cosmetic implements Serializable {
	private final Material material;
	private final Integer model;

	Cosmetic(final @NotNull Material material, final @Nullable Integer model) {
		this.material = material;
		this.model = model;
	}

	public Material getMaterial() {
		return this.material;
	}

	public Integer getModel() {
		return this.model;
	}
}

i want to serialize this for example. thanks in advance!

[TheMode]

The Tag API is ultimately a way to interact with a NBT Compound, so you can do anything using Tag.NBT and there is a dedicated Byte Array type present in the format: https://minecraft.fandom.com/wiki/NBT_format#Data_types

You would have to do something like

Tag<NBTByteArray> tag = Tag.class.cast(Tag.NBT("path"));

var handler = TagHandler.newHandler();
NBTByteArray byteArray = handler.getTag(tag);

For enums we do not have an util method for it, you have to choose between serializing the enum name using Tag.String, or its ordinal with Tag.Integer

// Store name
var handler = TagHandler.newHandler();
var tag = Tag.String("enum");
handler.setTag(tag, Test.A.name());

// Store ordinal
var handler = TagHandler.newHandler();
var tag = Tag.Integer("enum");
handler.setTag(tag, Test.A.ordinal());

// Store ordinal but use enum
var handler = TagHandler.newHandler();
Tag<Test> tag = Tag.Integer("enum").map(v -> Test.values()[v], Enum::ordinal);
handler.setTag(tag, Test.A);

As for your Cosmetic example I would first recommend to never use the Serializable interface, and you can use it in the tag API as follow

public record Cosmetic(String material, int model)  {
}
var handler = TagHandler.newHandler();
Tag<Cosmetic> tag = Tag.Structure("cosmetic", Cosmetic.class);
handler.setTag(tag, new Cosmetic("Something", 5));
Cosmetic cosmetic = handler.getTag(tag);

[Sombian]

thank you for your kind and fast responeses!
im really glad i can play without stupid NMS in Minestom's favour!