URLClassLoader - NoClassDefFoundError

[canelex]

Hello everyone, I am currently working on a mod that will allow you to load a plugin for it. In order to do this, I load Hub.class from and external plugin jar and register it in the event bus. This allows the plugin to listen for events and do whatever I need it to do. Here is how I load Hub.class:
 

@Mod(modid="Example", name="Example", version="0.1")
public class Example
{
	@Mod.EventHandler
	public void preInit(FMLPreInitializationEvent event)
	{
		loadClass();
	}
  
	private void loadClass()
	{
		try
		{
        		URL[] jarFile = new URL[] { new URL("file:///C:/LC/lc.jar") }; // This is the path to my jar file containing Hub.class
			URLClassLoader loader = new URLClassLoader(jarFile, this.getClass().getClassLoader()); // Create a URLClassLoader
			Class<?> classToLoad = Class.forName ("net.canelex.lc.Hub", false, loader); // Find the class Hub.class (package is correct)
			Object object = classToLoad.getConstructor().newInstance(); // Create a new instance of it.
			classToLoad.getDeclaredMethod("init").invoke(object); // Run method 'init'
		
		} catch (Exception e)
		{
			e.printStackTrace();
		}
	}
}

 

Here is the class Hub inside of an external plugin jar:

 

public class Hub
{
	
	public void init()
	{
		FMLCommonHandler.instance().bus().register(this); // Register itself into event bus.
		MinecraftForge.EVENT_BUS.register(this);
		System.out.println("Registered.");
	}
	
	@SubscribeEvent
	public void onKey(InputEvent.KeyInputEvent event)
	{
		System.out.println("Key Pressed!");
	}

}

 

So currently, the mod registers the Hub class to the event bus and prints "Registered" into the console. However, as soon as the player presses a key, NoClassDefFoundError is thrown and the game crashes. Because of this, I know that an instance of Hub.class was registered in the event bus, but when the event is called something goes wrong. Can anyone please help me fix this error / point out what I am doing wrong? Thanks!

 

java.lang.NoClassDefFoundError: net/canelex/lc/Hub
	at cpw.mods.fml.common.eventhandler.ASMEventHandler_6_Hub_onKey_KeyInputEvent.invoke(.dynamic) ~[?:?]
	at cpw.mods.fml.common.eventhandler.ASMEventHandler.invoke(ASMEventHandler.java:54) ~[ASMEventHandler.class:?]
	at cpw.mods.fml.common.eventhandler.EventBus.post(EventBus.java:140) [EventBus.class:?]
	at cpw.mods.fml.common.FMLCommonHandler.fireKeyInput(FMLCommonHandler.java:540) [FMLCommonHandler.class:?]
	at net.minecraft.client.Minecraft.func_71407_l(Minecraft.java:1873) [bao.class:?]
	at net.minecraft.client.Minecraft.func_71411_J(Minecraft.java:973) [bao.class:?]
	at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:898) [bao.class:?]
	at net.minecraft.client.main.Main.main(SourceFile:148) [Main.class:?]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:1.8.0_25]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:1.8.0_25]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:1.8.0_25]
	at java.lang.reflect.Method.invoke(Method.java:483) ~[?:1.8.0_25]
	at net.minecraft.launchwrapper.Launch.launch(Launch.java:135) [launchwrapper-1.12.jar:?]
	at net.minecraft.launchwrapper.Launch.main(Launch.java:28) [launchwrapper-1.12.jar:?]
Caused by: java.lang.ClassNotFoundException: net.canelex.lc.Hub
	at java.lang.ClassLoader.findClass(ClassLoader.java:530) ~[?:1.8.0_25]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:424) ~[?:1.8.0_25]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[?:1.8.0_25]
	... 14 more

 

Edited March 4, 2017 by canelex
Spelling

[canelex]

6 hours ago, diesieben07 said:

May I ask why? Just put the "plugin" jar into the mods folder and it will be added to the classpath automatically.

If I did that it would be loaded as a mod itself. Pus, I eventually want to make it so that you can load plugins at runtime.

[larsgerrits]

49 minutes ago, canelex said:

If I did that it would be loaded as a mod itself.

 

Only if the jar file has a file annotated by @Mod. Other JAR files won't get loaded as mods and will simply be put in the classpath.

 

50 minutes ago, canelex said:

Pus, I eventually want to make it so that you can load plugins at runtime.

 

There are certain things which can only be done on game startup (i.e. block/item registry), so you won't be able to add those at runtime.

[LexManos]

Side not why are you writing this for 1.7.10-?

[canelex]

5 hours ago, LexManos said:

Side not why are you writing this for 1.7.10-?

That's the version that most of the servers I play on are.

[canelex]

On 3/5/2017 at 10:41 AM, larsgerrits said:

Only if the jar file has a file annotated by @Mod. Other JAR files won't get loaded as mods and will simply be put in the classpath.

 

There are certain things which can only be done on game startup (i.e. block/item registry), so you won't be able to add those at runtime.

Thank you! Putting the plugin jar in the mod folder did the trick!