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1.19.2 Writing and reading HashMap server -> client buf.writeMap() and buf.readMap()


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Hello everyone, I'm new, I'm working on an RPG mod and have achieved good results

now I'm working on compressing the package system, namely, I want to combine all the player variable synchronization packages into one multifunctional package

at the moment I have to synchronize each player characteristic with a separate package, because if you combine all the characteristics in one package, then in my opinion this will give a huge load on the server with good online

I want to write a package that will send data to the client in the form of a HashMap()

something like this: if the player's experience is updated, The server sends to the client Map<"exp", 200 000>

If the level of the player has changed during the increase in experience, the server sends to the client Map<"exp", 200 000><"lvl", 3>

The client, having received this packet, reads the entire HashMap in turn, and updates only those data that have been changed and transmitted


I am facing the following difficulties:

1. buf.writeMap(Map<K, V> p_236832_, FriendlyByteBuf.Writer<K> p_236833_, FriendlyByteBuf.Writer<V> p_236834_)

as far as I understand Map<K, V> p_236832_  the read source is passed to this parameter, namely the Map() object, I managed to send it

FriendlyByteBuf.Writer<K> & FriendlyByteBuf.Writer<V> I don’t understand how to format it correctly, after many attempts and sorting through everything I already know, it turned out to make these parameters accepted through lambdas and did not cause errors, but most likely it was not correct

2. buf.readMap(FriendlyByteBuf.Reader<K> p_236848_, FriendlyByteBuf.Reader<V> p_236849_)

FriendlyByteBuf.Reader<K> & FriendlyByteBuf.Reader<V> What is it?

because the method returns this.readMap(Maps::newHashMapWithExpectedSize, p_236848_, p_236849_);

I realized that there is a bork in a new map, but again I don’t understand how to count from the transferred map keys & values

please help me to write these two methods in correct syntax

show any example, at least in which it will be clear what data is passed to these methods

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It seems that I won one part, but still not completely

public void toBytes(Map<String, Long> map,FriendlyByteBuf buf) {
(friendlyByteBuf, s) -> {},   (friendlyByteBuf, aLong) -> {});


But it's still not right, is it?

and how to arrange {....} ?


following the logic, I wrote this

public void toBytes(Map<String, Long> map,FriendlyByteBuf buf) {
buf.writeMap(map, FriendlyByteBuf::writeUtf, FriendlyByteBuf::writeLong);


in short, I won

Edited by andreybadrey
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I saw that the forum was also interested in this topic, so I will prescribe the package template

import com.bodryak.gmod.variables.client.PDC;
import com.google.common.collect.Maps;
import net.minecraft.network.FriendlyByteBuf;
import net.minecraftforge.network.NetworkEvent;

import java.util.Map;
import java.util.function.Supplier;

public class PDSyncS2CPacket {
    private final Map<String, Long> toSync ;

    public PDSyncS2CPacket(Map<String, Long> map) {
        this.toSync = map;

    public PDSyncS2CPacket(FriendlyByteBuf buf) {
        this.toSync = buf.readMap(Maps::newHashMapWithExpectedSize,FriendlyByteBuf::readUtf, FriendlyByteBuf::readLong);

    public void toBytes(FriendlyByteBuf buf) {
        buf.writeMap(this.toSync, FriendlyByteBuf::writeUtf, FriendlyByteBuf::writeLong);

    public boolean handle(Supplier<NetworkEvent.Context> supplier) {
        NetworkEvent.Context context = supplier.get();
        context.enqueueWork(() -> {
            // HERE WE ARE ON THE CLIENT!
            if (this.toSync.get("lvl") != null){
                System.out.println("Server send lvl " + this.toSync.get("lvl"));
            if (this.toSync.get("exp") != null){
                System.out.println("server send exp " + this.toSync.get("exp"));
            if (this.toSync.get("nlv") != null){
                System.out.println("server send exp to next lvl " + this.toSync.get("nlv"));

        return true;

Please, I beg you, if all this is not written correctly, give feedback

Edited by andreybadrey
fix error
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