[1.16.2] How Do I Properly Implement Global Loot Modifiers?

[HeyImAmethyst]

I'm trying to make it so that witches drop a custom item I made. I read that I needed to use global loot modifiers and I am currently looking at the documentation as well as other posts online about how to use them and I can't seem to fully understand what I need to put in my code.

 

This is my what I have in my global_loot_modifiers.json:

{
  "replace": false,
  "entries": [
    "global_loot_test:witch"
  ]
}

 

my witch.json:

{
  "type": "mwh:dust_drop",

  "conditions": 
  [
    {
      "condition": "minecraft:killed_by_player"
    },
    
    {
		"condition": "minecraft:entity_properties",
		"predicate": {
		  "type": "minecraft:witch"
		},
		"entity": "this"
	}
  ],
  
  "item": "mwh:witch_dust"
}

 

and my modifier class:

class VanillaMobModifier extends LootModifier 
{
    private final int numSeedsToConvert;
    private final Item itemToCheck;
    private final Item itemReward;
    
    public VanillaMobModifier(ILootCondition[] conditionsIn, int numSeeds, Item itemCheck, Item reward) 
    {
        super(conditionsIn);
        numSeedsToConvert = numSeeds;
        itemToCheck = itemCheck;
        itemReward = reward;
    }

    @Nonnull
    @Override
    public List<ItemStack> doApply(List<ItemStack> generatedLoot, LootContext context) {
        //
        // Additional conditions can be checked, though as much as possible should be parameterized via JSON data.
        // It is better to write a new ILootCondition implementation than to do things here.
        //
        int numSeeds = 0;
        for(ItemStack stack : generatedLoot) 
        {
            if(stack.getItem() == itemToCheck)
                numSeeds+=stack.getCount();
        }
        if(numSeeds >= numSeedsToConvert) 
        {
            generatedLoot.removeIf(x -> x.getItem() == itemToCheck);
            generatedLoot.add(new ItemStack(itemReward, (numSeeds/numSeedsToConvert)));
            numSeeds = numSeeds%numSeedsToConvert;
            if(numSeeds > 0)
                generatedLoot.add(new ItemStack(itemToCheck, numSeeds));
        }
        return generatedLoot;
    }
    
    @SuppressWarnings("unused")
	private static class Serializer extends GlobalLootModifierSerializer<VanillaMobModifier> 
    {

        @Override
        public VanillaMobModifier read(ResourceLocation name, JsonObject object, ILootCondition[] conditionsIn) {
            int numSeeds = JSONUtils.getInt(object, "numSeeds");
            Item seed = ForgeRegistries.ITEMS.getValue(new ResourceLocation((JSONUtils.getString(object, "seedItem"))));
            Item wheat = ForgeRegistries.ITEMS.getValue(new ResourceLocation(JSONUtils.getString(object, "replacement")));
            return new VanillaMobModifier(conditionsIn, numSeeds, seed, wheat);
        }

    	@Override
    	public JsonObject write(VanillaMobModifier instance)
    	{
    		// TODO Auto-generated method stub
    		return null;
    	}
    }
}

 

I don't know how to modify this part of the code to fit my needs. I only want just witches to have a chance at dropping my item when killed.

 

 

And I saw that I needed to do something like this:

 

@SubscribeEvent
    public static void registerModifierSerializers(@Nonnull final RegistryEvent.Register<GlobalLootModifierSerializer<?>> event) 
    {
        if (ENABLE) 
        {
            event.getRegistry().register(new VanillaMobDropsModifier.Serializer().setRegistryName(new ResourceLocation(MOD_ID,"dust_drop")));
        } 
    }

 

buts it's giving me errors. Pretty sure I'm missing something. I bet I'm probably missing important or obvious but if anyone can point me in the right direction I would very my appreciate it.

[Draco18s]

6 hours ago, HeyImAmethyst said:

I don't know how to modify this part of the code to fit my needs. I only want just witches to have a chance at dropping my item when killed.

Under the assumption that your condition is only ever true for witches (I haven't messed with entity predicates, so I am not sure that your condition is actually what you want) the "alter this section" is very easy:

    @Nonnull
    @Override
    public List<ItemStack> doApply(List<ItemStack> generatedLoot, LootContext context) {
        generatedLoot.add(new ItemStack(dust, 1));
        return generatedLoot;
    }

You would have a field for the dust that you would deserialize to (look at how the reward field is deserialized) and would not need the other two fields at all.

[HeyImAmethyst]

On 10/23/2020 at 1:43 AM, Draco18s said:

Under the assumption that your condition is only ever true for witches (I haven't messed with entity predicates, so I am not sure that your condition is actually what you want) the "alter this section" is very easy:

    @Nonnull
    @Override
    public List<ItemStack> doApply(List<ItemStack> generatedLoot, LootContext context) {
        generatedLoot.add(new ItemStack(dust, 1));
        return generatedLoot;
    }

You would have a field for the dust that you would deserialize to (look at how the reward field is deserialized) and would not need the other two fields at all.

 

Okay so I changed it, and I doubled and triple checked to see if I have everything written right and my .json files in the right place. But in my error log it is giving me this error
 

[m[1;31m[12:11:24] [Render thread/ERROR] [ne.mi.co.lo.LootModifierManager/]: Couldn't parse loot modifier mwh:dust_drop
java.lang.NullPointerException: Cannot invoke "com.google.gson.JsonElement.isJsonObject()" because "element" is null
	at net.minecraftforge.common.loot.LootModifierManager.deserializeModifier(LootModifierManager.java:130) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading}
	at net.minecraftforge.common.loot.LootModifierManager.lambda$apply$0(LootModifierManager.java:118) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading}
	at java.util.ArrayList.forEach(ArrayList.java:1511) ~[?:?] {}
	at net.minecraftforge.common.loot.LootModifierManager.apply(LootModifierManager.java:116) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading}
	at net.minecraftforge.common.loot.LootModifierManager.apply(LootModifierManager.java:57) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading}
	at net.minecraft.client.resources.ReloadListener.lambda$reload$1(ReloadListener.java:14) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading}
	at java.util.concurrent.CompletableFuture$UniAccept.tryFire(CompletableFuture.java:714) ~[?:?] {}
	at java.util.concurrent.CompletableFuture$Completion.run(CompletableFuture.java:478) ~[?:?] {}
	at net.minecraft.resources.AsyncReloader.lambda$new$3(AsyncReloader.java:66) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading}
	at net.minecraft.util.concurrent.ThreadTaskExecutor.run(ThreadTaskExecutor.java:139) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.util.concurrent.RecursiveEventLoop.run(RecursiveEventLoop.java:22) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading}
	at net.minecraft.util.concurrent.ThreadTaskExecutor.driveOne(ThreadTaskExecutor.java:109) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.util.concurrent.ThreadTaskExecutor.driveUntil(ThreadTaskExecutor.java:122) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.client.Minecraft.func_238189_a_(Minecraft.java:1866) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
	at net.minecraft.client.Minecraft.func_238195_a_(Minecraft.java:1719) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
	at net.minecraft.client.Minecraft.func_238191_a_(Minecraft.java:1689) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
	at net.minecraft.client.gui.screen.WorldSelectionList$Entry.func_214443_e(WorldSelectionList.java:364) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.gui.screen.WorldSelectionList$Entry.func_214438_a(WorldSelectionList.java:273) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.gui.screen.WorldSelectionList$Entry.func_231044_a_(WorldSelectionList.java:228) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.gui.widget.list.AbstractList.func_231044_a_(AbstractList.java:292) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.gui.INestedGuiEventHandler.func_231044_a_(INestedGuiEventHandler.java:31) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.MouseHelper.lambda$mouseButtonCallback$0(MouseHelper.java:92) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.gui.screen.Screen.func_231153_a_(Screen.java:425) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.MouseHelper.mouseButtonCallback(MouseHelper.java:90) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.MouseHelper.lambda$registerCallbacks$4(MouseHelper.java:185) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.util.concurrent.ThreadTaskExecutor.execute(ThreadTaskExecutor.java:86) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:accesstransformer:B}
	at net.minecraft.client.MouseHelper.lambda$registerCallbacks$5(MouseHelper.java:184) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at org.lwjgl.glfw.GLFWMouseButtonCallbackI.callback(GLFWMouseButtonCallbackI.java:36) ~[lwjgl-glfw-3.2.2.jar:build 10] {}
	at org.lwjgl.system.JNI.invokeV(Native Method) ~[lwjgl-3.2.2.jar:build 10] {}
	at org.lwjgl.glfw.GLFW.glfwPollEvents(GLFW.java:3101) ~[lwjgl-glfw-3.2.2.jar:build 10] {}
	at com.mojang.blaze3d.systems.RenderSystem.flipFrame(RenderSystem.java:93) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.MainWindow.flipFrame(MainWindow.java:304) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at net.minecraft.client.Minecraft.runGameLoop(Minecraft.java:1010) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
	at net.minecraft.client.Minecraft.run(Minecraft.java:589) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:accesstransformer:B,pl:runtimedistcleaner:A}
	at net.minecraft.client.main.Main.main(Main.java:184) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {re:classloading,pl:runtimedistcleaner:A}
	at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?] {}
	at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:?] {}
	at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?] {}
	at java.lang.reflect.Method.invoke(Method.java:564) ~[?:?] {}
	at net.minecraftforge.userdev.FMLUserdevClientLaunchProvider.lambda$launchService$0(FMLUserdevClientLaunchProvider.java:55) ~[forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {}
	at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:37) [modlauncher-7.0.1.jar:?] {}
	at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:54) [modlauncher-7.0.1.jar:?] {}
	at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:72) [modlauncher-7.0.1.jar:?] {}
	at cpw.mods.modlauncher.Launcher.run(Launcher.java:81) [modlauncher-7.0.1.jar:?] {}
	at cpw.mods.modlauncher.Launcher.main(Launcher.java:65) [modlauncher-7.0.1.jar:?] {}
	at net.minecraftforge.userdev.LaunchTesting.main(LaunchTesting.java:105) [forge-1.16.2-33.0.61_mapped_snapshot_20200514-1.16-recomp.jar:?] {}

 

Its saying that "element" is null but I don't know what its referring to. Is it something is the doApply method or is it something in my Serializer? I removed somethings in my Serializer so it looks like this now:

 

private static abstract class Serializer extends GlobalLootModifierSerializer<VanillaMobModifier> 
    {

       @Override
       public VanillaMobModifier read(ResourceLocation name, JsonObject object, ILootCondition[] conditionsIn) 
       {
           Item dust = ForgeRegistries.ITEMS.getValue(new ResourceLocation(JSONUtils.getString(object, "item")));
           return new VanillaMobModifier(conditionsIn, dust);
       }

    }

 

I noticed that in the documentation that the class was private and static but for me it gives me an error saying to add unimplemented methods or to make it abstract. when I click on add unimplemented methods, this method is added:

 

	@Override
	public JsonObject write(VanillaMobModifier instance)
	{
		// TODO Auto-generated method stub
		return null;
	}

 

Making it abstract removes the error line under Serializer but I would still this NullPointerException error.

 

[Draco18s]

2 hours ago, HeyImAmethyst said:

[m[1;31m[12:11:24] [Render thread/ERROR] [ne.mi.co.lo.LootModifierManager/]: Couldn't parse loot modifier mwh:dust_drop java.lang.NullPointerException: Cannot invoke "com.google.gson.JsonElement.isJsonObject()" because "element" is null

Your json file does not match your deserialization method. You need to make your deserialize (the read method) match your json structure.

 

2 hours ago, HeyImAmethyst said:

Making it abstract removes the error line under

No, do not do this. Actually implement the method. It should mirror your deserialization method, so that your json file is generated by it and properly deserializes.

Edited October 24, 2020 by Draco18s

[HeyImAmethyst]

1 hour ago, Draco18s said:

Your json file does not match your deserialization method. You need to make your deserialize (the read method) match your json structure.

 

It doesn't? Wait so the does read method reads the json file and the write method writes it out? What would I need to put in read method then? Because in the documentation it says that the conditions are already deserialized or was that specific to that code? Im looking online about reading and writing json files and I saw these:

https://stackoverflow.com/questions/10926353/how-to-read-json-file-into-java-with-simple-json-library
https://stackoverflow.com/questions/2591098/how-to-parse-json-in-java
https://www.geeksforgeeks.org/parse-json-java/

 

Is that what I need to do? Like figure out how to map the code to the json?

[Draco18s]

2 hours ago, HeyImAmethyst said:

Wait so the does read method reads the json file and the write method writes it out?

GASP. WHO'D HAVE GUESSED.

Yes, yes it does.

That's literally why they are there. Json resources aren't magic.

2 hours ago, HeyImAmethyst said:

Because in the documentation it says that the conditions are already deserialized or was that specific to that code?

Conditions are automatically deserialized.

Not the rest of it. Conditions are JUST this part:

On 10/22/2020 at 5:47 PM, HeyImAmethyst said:

  "conditions": 
  [
    {
      "condition": "minecraft:killed_by_player"
    },
    
    {
		"condition": "minecraft:entity_properties",
		"predicate": {
		  "type": "minecraft:witch"
		},
		"entity": "this"
	}
  ],

 

2 hours ago, HeyImAmethyst said:

Like figure out how to map the code to the json?

...yes

You have custom data. So read your custom data.

[HeyImAmethyst]

On 10/24/2020 at 7:57 PM, Draco18s said:

GASP. WHO'D HAVE GUESSED.

Yes, yes it does.

That's literally why they are there. Json resources aren't magic.

 

Yea, I realized how obvious it was after I wrote my comment XD. I'm going to try and get this to work. Thanks for your help!