Save a list of objects as .json on server side

[Bumpay]

Hello,
to give a short summary, my mod should allow players on a server to create a port and save ships as structures. Players can then teleport with their ship to other ports.

Here comes the problem, I don't know how to save a list of ports on the server as .json.

Also I would like to be able to add new entries to the .json.

When I try to make it client-sided the client crashes.

public void addToPortList() {

	Gson gson = new GsonBuilder().create();
	try {
		Writer writer = new FileWriter("../ports.json");
        gson.toJson(this, writer);
    }catch(IOException e){
        e.printStackTrace();
	}
}

With kind regards,
Bumpay

[Bumpay]

Can you provide a code example or how I can implement it with both of your mentioned options? Because it is hard for me to understand the documentation from forge.

Edited September 30, 2020 by Bumpay

[Bumpay]

2 hours ago, diesieben07 said:

Not at all. Don't create your own system for saving data.

Use WorldSavedData or capabilities.

And is WorldSavedData  even up to date in 1.15.2 ? Because i can't import the class MapStorage.

[Bumpay]

1 hour ago, diesieben07 said:

No, it seems to not be up to date. You have to call ServerWorld#getSavedData, which will give you a DimensionSavedDataManager, this allows you to get / save an instance of your WorldSavedData.

Do you have a source where I can get the newer documentation, as it is hard for me to find any because I have no clue what is how possible with forge 1.15.2. I can only find videos from the older versions of minecraft.

[Bumpay]

Do you know in which parts of the game they use WorldSaveData? And is there even a decompiled variant of the 1.15.2 jar ?

 

[Bumpay]

I think I don't have it in my project as it seems...

[Bumpay]

2 minutes ago, Bumpay said:

I think I don't have it in my project as it seems...

 

30 minutes ago, diesieben07 said:

You have the decompiled code as part of your workspace. You can use normal IDE functions to search it, such as looking for usages of the WorldSavedData class.

Nevermind found it. 🥴

[Bumpay]

@diesieben07 do you know how I can add NBT Tags to the level.dat file?

[Bumpay]

1 hour ago, diesieben07 said:

What for? Do not modify level.dat.

I want to store a list of Objects on the serverside.

 

Basically what I am trying to do is to store all created Shipports as a List on the Serverside. But it should be able to add/delete and get ports from/to the list.

 

You showed me the WorldSavedData method but I couldn't find any goo example of how to use it so I searched for different methods.

 

I am not bad at programming but it is hard to figure out how minecraft work with different things.

[Bumpay]

package com.bumpay.travelsimplified.trasim.port;

import net.minecraft.nbt.CompoundNBT;
import net.minecraft.world.server.ServerWorld;
import net.minecraft.world.storage.DimensionSavedDataManager;
import net.minecraft.world.storage.WorldSavedData;

public class PortWorldSavedData extends WorldSavedData {

    private static final String NAME = "TraSim_PortData";

    public PortWorldSavedData() {
        super(NAME);
    }

    public PortWorldSavedData(String name) {
        super(name);
    }

    @Override
    public void read(CompoundNBT nbt) {
        
    }

    @Override
    public CompoundNBT write(CompoundNBT compound) {
        return null;
    }

    public static PortWorldSavedData get(ServerWorld world) {
        DimensionSavedDataManager data = world.getSavedData();
        PortWorldSavedData instance = (PortWorldSavedData) data.getOrCreate(PortWorldSavedData), NAME);
    }
}

And I do get an error on

PortWorldSavedData instance = (PortWorldSavedData) data.getOrCreate(PortWorldSavedData), NAME);

I tried to do it like in the Decumentations of Forge

[Draco18s]

5 minutes ago, Bumpay said:

And I do get an error on

What's the error?

[Bumpay]

1 minute ago, Draco18s said:

What's the error?

error: cannot find symbol
        PortWorldSavedData instance = (PortWorldSavedData) data.getOrCreate(PortWorldSavedData, NAME);
                                                                            ^

 

[Bumpay]

Can I just set the suplier to null, because it will create it then with the getOrCreate method? Or is this not how to use it?

[DaemonUmbra]

Do you know Java or are you trying to learn Java through modding?

[Draco18s]

3 hours ago, Bumpay said:

getOrCreate(PortWorldSavedData, NAME)

That is not valid Java. PortWorldSavedData is a Type, not an Object.

Edited September 30, 2020 by Draco18s

[Bumpay]

7 hours ago, DaemonUmbra said:

Do you know Java or are you trying to learn Java through modding?

I do know coding in Java. The only things I am struggeling with are the classes from minecraft as I don't know which are there and how to use them.

6 hours ago, Draco18s said:

That is not valid Java. PortWorldSavedData is a Type, not an Object.

Yeah I changed it, I did not recognize, that I tried something different there and forgot to type it back.

 

 

[Bumpay]

This is how it looks now:

package com.bumpay.travelsimplified.trasim.port;

import net.minecraft.nbt.CompoundNBT;
import net.minecraft.world.server.ServerWorld;
import net.minecraft.world.storage.DimensionSavedDataManager;
import net.minecraft.world.storage.WorldSavedData;

import java.util.function.Supplier;

public class PortWorldSavedData extends WorldSavedData {

    private static final String NAME = "TraSim_PortData";

    public PortWorldSavedData() {
        super(NAME);
    }

    public PortWorldSavedData(String name) {
        super(name);
    }

    @Override
    public void read(CompoundNBT nbt) {

    }

    @Override
    public CompoundNBT write(CompoundNBT compound) {
        return null;
    }

    public static PortWorldSavedData get(ServerWorld world) {
        DimensionSavedDataManager data = world.getSavedData();
        PortWorldSavedData instance = (PortWorldSavedData) data.getOrCreate(() -> {return null;}, NAME);

        if(instance == null) {
            instance = new PortWorldSavedData();
        }

        return instance;
    }
}

But as described in the Docs, I guess I shouldn't just pass a null pointer in the getOrCreate function.

 

I also tried PortWorldSavedData.class there like in the Docs but it sais it is a Supplier<T> needed.

public static PortWorldSavedData get(ServerWorld world) {
        DimensionSavedDataManager data = world.getSavedData();
        PortWorldSavedData instance = (PortWorldSavedData) data.getOrCreate(PortWorldSavedData.class, NAME);

        if(instance == null) {
            instance = new PortWorldSavedData();
        }

        return instance;
    }

 

So I also tried new Supplier<PortWorldSavedData> which added the abstract method within the parameter-section

public static PortWorldSavedData get(ServerWorld world) {
        DimensionSavedDataManager data = world.getSavedData();
        PortWorldSavedData instance = (PortWorldSavedData) data.getOrCreate(new Supplier<PortWorldSavedData>() {
            @Override
            public PortWorldSavedData get() {
                return null;
            }
        }, NAME);

        if(instance == null) {
            instance = new PortWorldSavedData();
        }

        return instance;
    }

 

And even though I don't actually know, if this is the right way to do it scince Forge updated but didn't update the Docs. Can someone confirm that I am not complete off the track?

[Bumpay]

Is this the right way of doing it?

public static PortWorldSavedData get(ServerWorld world) {
        DimensionSavedDataManager data = world.getSavedData();
        PortWorldSavedData instance = (PortWorldSavedData) data.getOrCreate(() -> {return new PortWorldSavedData();}, NAME);

        if(instance == null) {
            instance = new PortWorldSavedData();
        }

        return instance;
    }

 

[Bumpay]

4 minutes ago, diesieben07 said:

This is not needed.

They replaced it with the getOrCreate function, right?

[Bumpay]

So now I can save my list of objects with the WorldSavedData#write command?

Do I need to have a structure like this for my nbt?

Data	[NBT_Compound]
	Ports	[NBT_List]
		A single Port	[NBT_Compound]
			Name	[NBT_String]
			Owner	[NBT_List]
				A single player	[NBT_Compound]
					L	[NBT_Long]
					M	[NBT_Long]
			Docks	[NBT_List]
				A single dock	[NBT_Compound]
					isUsed	[NBT_Byte]
					isHome	[NBT_Byte]
					x1		[NBT_Double]
					y1		[NBT_Double]
					z1		[NBT_Double]
					x2		[NBT_Double]
					y2		[NBT_Double]
					z2		[NBT_Double]
			X	[NBT_Double]
			Z	[NBT_Double]

 

[Bumpay]

How can I set a directory where the .nbt file wil be saved?

[Bumpay]

And how do I create the structure in code?
I saw something like the CompoundNBT class, is this the one?

 

And if, is it done by declaring a CompoundNBT object in my WorldSavedData class and simply so compund.put... for every attribute that my object has?

 

Can you maybe give an example on a very simple Object so I can relate?

[Bumpay]

14 minutes ago, diesieben07 said:

You don't. It will be saved in a location that Minecraft sees fit based on the name you give to the WorldSavedData (it should include your ModID to avoid collisions).

 

No, this is what the writing and reading methods do. If you, for example, have the following class:

class MyObject {
   String value1;
   int value2;
}

And you wanted to store a list of these, then in your WorldSavedData you'd simply have a List<MyObject>. The conversion to and from NBT structure happens only in the responsible methods.

Sorry if I take long to get what you are trying me to do, but it is my first time working on minecraft or forge.

 

So to safe my List<Port> I have to write what? in the WorldSavedData#write function?

[Draco18s]

You loop over every Port in the list and break each one down into smaller pieces that can be saved.

[Bumpay]

My Port.class structure looks like this:

public class Port {
    private ServerPlayerEntity owner;
    private boolean isOpen = false;
    private String name;
    private int xCoordinate;
    private int zCoordinate;
    private List<Dock> docks;
}

 

And my thoughts brang me to this:

@Override
    public CompoundNBT write(CompoundNBT compound) {
        for (Port p:portList)
        {
            compound.putLong("uuidL", p.getOwner().getDisplayNameAndUUID());
            compound.putBoolean("isOpen", p.isOpen());
            compound.putString("name", p.getName());
            compound.putInt("x", p.getXCoordinate());
            compound.putInt("y", p.getZCoordinate());
            //list of Docks
        }
        return compound;
    }

Is this right? And how do I get the UUID of a player? Also my Port has a List of Docks, how do I write this in the compound? Another foreach?