So the goal I have is to have a file that is instantiated in memory while a particular world is running.  It will hold data that other pieces of the mod need to reference and change, no matter what chunks are loaded.  I want it to write to NBT when the world is closed and read from NBT when the world is opened.

 

It seems like this is thoroughly doable with capabilities, but I'm getting lost in the exact implementation.  Do I need to register it as a new capability with CapabilityManager, or can I use ICapabilitySerializable<NBTTagCompound>?  If so, how do I handle the hasCapability and getCapability functions?

 

Here the very small amount of code I have so far:

import net.minecraft.nbt.NBTTagCompound;

@SuppressWarnings("rawtypes")
public class VillageTracker implements net.minecraftforge.common.capabilities.ICapabilitySerializable<NBTTagCompound>
{
public int test;

public VillageTracker()
{

}

private void readFromNBT(NBTTagCompound nbt)
{
	if(nbt.hasKey("testInt"))
		test = nbt.getInteger("testInt");
}

private void writeToNBT(NBTTagCompound nbt) 
{
	nbt.setInteger("testInt", test);
}

@Override
public boolean hasCapability(net.minecraftforge.common.capabilities.Capability<?> capability, net.minecraft.util.EnumFacing facing)
    {
    }

@Override
    public <T> T getCapability(net.minecraftforge.common.capabilities.Capability<T> capability, net.minecraft.util.EnumFacing facing)
    {
    }

@Override
    public void deserializeNBT(NBTTagCompound nbt)
    {
        this.readFromNBT(nbt);
    }

@Override
    public NBTTagCompound serializeNBT()
    {
        NBTTagCompound nbt = new NBTTagCompound();
        this.writeToNBT(nbt);
        return nbt;
    }

}

Well, it doesn't necessarily need to be attached to the world, just saved and read in as NBT.  Its going to be values like a player's reputation with different factions, and those faction's relationship with each other, which should be visible (and editable) no matter which Faction Base Block is actually loaded.

 

Is WorldSavedData the best way to implement that?  This is deeper than I have yet dived into Forge, so I'm not even sure which classes to check out.

You can read and write NBT files outside of the Capabilities and WorldSavedData system.  It's a file like any other, run through CompressedStreamTools, IIRC.

All you need is a file to manage the alterations to the data and save/load that information using regular java io.

 

I use this during preInit to get the file location for my extra information

event.getModConfigurationDirectory().toString() +"\\LightDrafter\\Draftables.json"

which is just a custom folder inside of the config colder.

 

The biggest thing to remember is that the instance of this class will be different on server side and client side, so you will have to manage updates between them using IMessage and IMessageHandler, or make sure that you only create an instance when you are server side.

Well I went from not knowing how to do it to having three different options.  Thank you guys 

If your classes are only using simple types:

public class example{
String string;
int val;
Helper help;
}

public class Helper{
String info
}

 

you can use

Example ex = new Example();
String json = GsonBuilder.prettyPrinting().create().toJson(ex. Example.class);

and it will give you JSON as a string that you can then write to a file. Reading from the file is just as easy.

String json = //from file
Example ex = GsonBuilder.prettyPrinting().create().fromJson(json, Example.class);