Bukkit Java插件中的ClassNotFoundException

Question

I'm trying to revive a plugin and im geting thir error:

[03:01:18 ERROR]: Could not load 'plugins\Reporter.jar' in folder 'plugins'
org.bukkit.plugin.InvalidPluginException: java.lang.ClassNotFoundException: me.f
levasgr.rainbow.Reporter
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:184) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
        at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.
java:308) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
        at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager
.java:231) [craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
        at org.bukkit.craftbukkit.v1_7_R1.CraftServer.loadPlugins(CraftServer.ja
va:255) [craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
        at org.bukkit.craftbukkit.v1_7_R1.CraftServer.<init>(CraftServer.java:23
3) [craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
        at net.minecraft.server.v1_7_R1.PlayerList.<init>(PlayerList.java:63) [c
raftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
        at net.minecraft.server.v1_7_R1.DedicatedPlayerList.<init>(SourceFile:14
) [craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
        at net.minecraft.server.v1_7_R1.DedicatedServer.init(DedicatedServer.jav
a:126) [craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
        at net.minecraft.server.v1_7_R1.MinecraftServer.run(MinecraftServer.java
:424) [craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
        at net.minecraft.server.v1_7_R1.ThreadServerApplication.run(SourceFile:6
17) [craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
Caused by: java.lang.ClassNotFoundException: me.flevasgr.rainbow.Reporter
        at java.net.URLClassLoader$1.run(Unknown Source) ~[?:1.7.0_25]
        at java.net.URLClassLoader$1.run(Unknown Source) ~[?:1.7.0_25]
        at java.security.AccessController.doPrivileged(Native Method) ~[?:1.7.0_
25]
        at java.net.URLClassLoader.findClass(Unknown Source) ~[?:1.7.0_25]
        at org.bukkit.plugin.java.PluginClassLoader.findClass0(PluginClassLoader
.java:80) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
        at org.bukkit.plugin.java.PluginClassLoader.findClass(PluginClassLoader.
java:53) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
        at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.7.0_25]
        at java.lang.ClassLoader.loadClass(Unknown Source) ~[?:1.7.0_25]
        at java.lang.Class.forName0(Native Method) ~[?:1.7.0_25]
        at java.lang.Class.forName(Unknown Source) ~[?:1.7.0_25]
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.j
ava:173) ~[craftbukkit.jar:git-Bukkit-1.7.2-R0.2-b2974jnks]
        ... 9 more

I've done everything right! The plugin.yml the external jar and the export but still doesnt work. Any idea why?

Answer 1

As the error states,

java.lang.ClassNotFoundException: me.f levasgr.rainbow.Reporter

it cannot find the main class of your plugin. Perhaps one of your package names is capitalized, or your main class is lowercase. Bukkit's plugin loader is case sensitive when it comes to loading the main class.

Answer 2

There are different reasons for a java.lang.ClassNotFoundException in bukkit, the most common reason is that the plugin.yml doesn't point to the correct location.

If you have the following class:

package me.flevasgr.rainbow.reporter;
//...
public class Reporter {

Then you should copy the full package, place a dot and then place the name of the class, like this:

main: me.flevasgr.rainbow.reporter.Reporter 

This makes sure bukkit will find your class on the correct location.