I am trying to save information to a file on server side. My save method is getting triggered by WorldEvent.Save

 

I am getting this error when the world try's to save:

23:50:13] [server thread/ERROR] [FML]: Exception caught during firing event net.minecraftforge.event.world.WorldEvent$Save@7100ac37:
java.lang.ExceptionInInitializerError
at lidr.common.LiDrEvents.worldSave(LiDrEvents.java:32) ~[LiDrEvents.class:?]
...
Caused by: java.lang.NullPointerException
at lidr.common.DraftableReg.SaveDraftables(DraftableReg.java:57)

 

and my WorldSave Method:

@SubscribeEvent
public void worldSave(WorldEvent.Save e){
	if(!e.world.isRemote)
		DraftableReg.SaveDraftables(); // this is line 32
}

 

DraftableReg is a java "static" class meaning every field and method is static, private instructor with another field that instantiates it.

public final class DraftableReg {
public static final DraftableReg draftableReg = new DraftableReg();
        private static final URL LOCATION = draftableReg.getClass().getClassLoader().getResource("Draftables.json");

private DraftableReg(){
	DraftableMap dMap = new DraftableMap();
	dMap.AddPart(new TriTuple(0,0,0), new EdgePart(LuxinReg.RegisteredLuxin.get("Blue"), Purity.Base));
	RegisterDraftable(CoreFactory.GenerateFrom("test", CoreType.Sword, dMap)); //Testing items
}

public static void SaveDraftables(){
	try {
		GsonBuilder builder = new GsonBuilder();
		builder.registerTypeHierarchyAdapter(IDraftable.class, new DraftableAdapter<DraftingItemCore>());
		builder.enableComplexMapKeySerialization();
		builder.setPrettyPrinting();
		Gson gson = builder.create();
		BufferedWriter out = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(LOCATION.getFile()), "UTF-8"));
		gson.toJson(knowledgeBase, out); // this is line 57
	} catch (IOException e) {
		// TODO Auto-generated catch block
		e.printStackTrace();
	}

 

So obviously my URL is faulty. How should I be choosing a location to save to?

Yes, your save location is faulty because it is inside the JAR file.  You need to point to a location that has write access.

Thats what I can't figure out how to get. Lets say this is the folder structure:

/
   mods/
           LightDrafter.jar
           ...
   config/
           LightDrafter/
                   Draftables.json

How do I get the path/URL of Draftables.json

Client-side you can get the game directory from Minecraft#mcDataDir, server-side from MinecraftServer#getDataDirectory(), or you can get it in pre-init with FMLPreInitializationEvent#getModConfigurationDirectory().

You can also use FMLInitializationEvent#getSuggestedConfigurationFile() which you could manipulate to get the config directory

 

There's also Loader.instance().getConfigDir()