Troubleshooting ItemsAdder Plugin Loading Errors After Upgrade

July 12, 2025 by StackCamp Team 63 views

Troubleshooting Error Loading ItemsAdder Plugin After Upgrade

Upgrading plugins in Minecraft servers can sometimes be a delicate process. While new versions often bring exciting features and bug fixes, they can also introduce unexpected issues. One common problem that server administrators face is errors when loading plugins after an upgrade. This article delves into a specific case of an error encountered while upgrading the ItemsAdder plugin, a popular choice for adding custom items and resources to Minecraft servers. We will explore the error, its potential causes, and the steps you can take to troubleshoot and resolve it. By understanding the intricacies of plugin upgrades and common pitfalls, you can ensure a smoother experience for both yourself and your players.

Terms

[x] I'm using the very latest version of ItemsAdder and its dependencies.
[x] I am sure this is a bug and it is not caused by a misconfiguration or by another plugin.
[x] I've looked for already existing issues on the Issue Tracker and haven't found any.
[x] I already searched on the plugin wiki to know if a solution is already known.
[x] I searched the #itemsadder-forum channel on Discord for similar issues.
[x] I tested that this issue persists on a bare-minimum Server as described in #4187.

Discord Username (optional)

No response

What happened?

could not load resourcepack

Steps to reproduce the issue

was using 4.0.10, everything working flawlessly then I upgrade to 4.0.11 (remove old jar and move new jar) once IA is loaded, it will output errors

Server version

This server is running Paper version 1.21.1-132-ver/1.21.1@b48403b (2024-11-21T10:14:27Z) (Implementing API version 1.21.1-R0.1-SNAPSHOT)

ItemsAdder Version

ItemsAdder version 4.0.11

ProtocolLib Version

ProtocolLib version 5.4.0-SNAPSHOT-739

LoneLibs Version

No response

Full Server Log

https://mclo.gs/jkTCobx

Error (optional)

[15:12:03] [Server thread/ERROR]: ItemsAdder) Error loading the plugin, something is not configured right or an exception occured. More detail:
[15:12:03] [Server thread/WARN]: java.lang.ClassCastException: class net.minecraft.core.MappedRegistry$1 cannot be cast to class net.minecraft.core.MappedRegistry (net.minecraft.core.MappedRegistry$1 and net.minecraft.core.MappedRegistry are in unnamed module of loader java.net.URLClassLoader @5eb5c224)
[15:12:03] [Server thread/WARN]: 	at ItemsAdder_4.0.11.jar//itemsadder.m.vc.t(SourceFile:123)
[15:12:03] [Server thread/WARN]: 	at ItemsAdder_4.0.11.jar//itemsadder.m.lz.jl(SourceFile:1489)
[15:12:03] [Server thread/WARN]: 	at ItemsAdder_4.0.11.jar//itemsadder.m.a.b(SourceFile:877)
[15:12:03] [Server thread/WARN]: 	at ItemsAdder_4.0.11.jar//itemsadder.m.a.c(SourceFile:651)
[15:12:03] [Server thread/WARN]: 	at ItemsAdder_4.0.11.jar//itemsadder.m.afo.f(SourceFile:144)
[15:12:03] [Server thread/WARN]: 	at ItemsAdder_4.0.11.jar//itemsadder.m.a.a(SourceFile:645)
[15:12:03] [Server thread/WARN]: 	at ItemsAdder_4.0.11.jar//itemsadder.m.a.a(SourceFile:295)
[15:12:03] [Server thread/WARN]: 	at ItemsAdder_4.0.11.jar//dev.lone.itemsadder.Main.ls(SourceFile:513)
[15:12:03] [Server thread/WARN]: 	at ItemsAdder_4.0.11.jar//dev.lone.itemsadder.Main.onEnable(SourceFile:404)
[15:12:03] [Server thread/WARN]: 	at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:288)
[15:12:03] [Server thread/WARN]: 	at io.papermc.paper.plugin.manager.PaperPluginInstanceManager.enablePlugin(PaperPluginInstanceManager.java:202)
[15:12:03] [Server thread/WARN]: 	at io.papermc.paper.plugin.manager.PaperPluginManagerImpl.enablePlugin(PaperPluginManagerImpl.java:109)
[15:12:03] [Server thread/WARN]: 	at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:520)
[15:12:03] [Server thread/WARN]: 	at org.bukkit.craftbukkit.CraftServer.enablePlugin(CraftServer.java:641)
[15:12:03] [Server thread/WARN]: 	at net.minecraft.server.MinecraftServer.loadWorld0(MinecraftServer.java:753)
[15:12:03] [Server thread/WARN]: 	at net.minecraft.server.MinecraftServer.loadLevel(MinecraftServer.java:515)
[15:12:03] [Server thread/WARN]: 	at net.minecraft.server.dedicated.DedicatedServer.initServer(DedicatedServer.java:329)
[15:12:03] [Server thread/WARN]: 	at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1214)
[15:12:03] [Server thread/WARN]: 	at net.minecraft.server.MinecraftServer.lambda$spin$0(MinecraftServer.java:329)
[15:12:03] [Server thread/WARN]: 	at java.base/java.lang.Thread.run(Thread.java:1583)

Problematic items yml configuration file (optional)

Other files, you can drag and drop them here to upload. (optional)

No response

Screenshots/Videos (you can drag and drop files or paste links)

No response

Understanding the ItemsAdder Plugin and Resource Packs

Before diving into the specifics of the error, let's briefly discuss the ItemsAdder plugin and its use of resource packs. ItemsAdder is a powerful plugin for Minecraft servers that allows server owners to add custom items, blocks, and other resources to their game. This plugin relies heavily on resource packs, which are collections of assets like textures, models, and sounds that change the appearance and feel of the game. When ItemsAdder is updated, it sometimes requires changes to the resource pack to function correctly with the new version. Failing to update the resource pack can lead to errors and prevent the plugin from loading properly.

Resource packs are crucial for the ItemsAdder plugin because they provide the visual and auditory elements that make the custom items and blocks unique. When a server owner upgrades ItemsAdder, the plugin might introduce new features, fix bugs, or change how certain assets are handled. These changes often necessitate corresponding updates to the resource pack. For instance, a new version of ItemsAdder might use a different texture format or require additional metadata for custom items. If the resource pack is not updated to reflect these changes, the plugin may fail to load, resulting in errors like the one we are troubleshooting.

When troubleshooting resource pack loading issues with ItemsAdder, it’s essential to understand the relationship between the plugin version and the resource pack version. The ItemsAdder documentation and community forums often provide guidance on which resource pack version is compatible with specific plugin versions. Keeping both the plugin and the resource pack up-to-date and compatible is a key step in preventing loading errors. Additionally, ensuring that the resource pack is correctly installed on the server and properly configured in the server.properties file is crucial. This includes verifying the resource pack's file integrity and ensuring that the server is set up to force players to download and use the resource pack upon joining.

Analyzing the Error: ClassCastException

The core of the issue lies in the ClassCastException detailed in the error log. This Java exception occurs when the program attempts to cast an object of one class to another class that it is not compatible with. In this specific case, the error message indicates that a net.minecraft.core.MappedRegistry$1 cannot be cast to net.minecraft.core.MappedRegistry. This suggests a fundamental incompatibility between the classes being used by the ItemsAdder plugin and the Minecraft server's core libraries.

The ClassCastException is a common indicator of underlying issues with class loading or version mismatches. In the context of a Minecraft plugin, this often means that the plugin is trying to use a class or method in a way that is not supported by the server's version or that there are conflicting versions of the same library loaded. For ItemsAdder, which interacts deeply with the server's item registry and resource handling, such an error can prevent the plugin from initializing correctly. The stack trace provided in the error log gives further clues by showing the sequence of method calls that led to the exception, starting from the ItemsAdder plugin's code (itemsadder.m.vc.t) and going through various internal methods related to item registration and loading.

To effectively address this ClassCastException, it's crucial to consider the version compatibility between ItemsAdder, the Minecraft server (Paper 1.21.1 in this case), and any other related libraries like ProtocolLib. Mismatched versions can result in class loading conflicts, where the plugin expects a certain structure or behavior from a class that the server (or another library) provides differently. This analysis emphasizes the importance of verifying that all components of the server setup are aligned in terms of versions and dependencies, a key step in troubleshooting plugin loading errors.

Investigating Potential Causes

Several factors might contribute to the