I am currently making a small plugin framework for a program in Java.
Basically GRPluginManager.loadPlugins() loops trough all jar files in a directory, then reads the name of the Main-class of this plugin from a specific file inside of the jar and loads it into the classpath. After that it calls the enable() method of this plugin-Main-class (which extends GRPlugin).
However, it doesn't work. It looks like the loading of the plugin-Main-class works fine and only the parent class (GRPlugin) can not be found. But it definitely exists.
GRPlugin.java
package io.github.grengine.core.plugins;
public class GRPlugin {
public void enable(){
}
public void disable(){
}
}
GRPluginManager.java
package io.github.grengine.core.plugins;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.Map;
import java.util.zip.ZipEntry;
import java.util.zip.ZipFile;
import org.bukkit.plugin.java.JavaPluginLoader;
import org.yaml.snakeyaml.Yaml;
import io.github.grengine.JarUtils;
import io.github.grengine.Log;
import io.github.grengine.Main;
public class GRPluginManager {
private static final String PLUGIN_PATH = Main.main.getDataFolder()+File.separator+"storage"+File.separator+"plugins";
private ArrayList<GRPlugin> plugins = new ArrayList<GRPlugin>();
public ArrayList<GRPlugin> loadPlugins() throws Exception{
File filePath = new File(PLUGIN_PATH);
File files [] = filePath.listFiles();
//Iterate over files in the plugin directory
for(File file:files){
if(file.isFile()){
Log.Info("Reading "+file);
ZipFile zipFile = new ZipFile(file);
String fullyQualifiedName = null;
String plname = null;
String plversion = null;
Enumeration<? extends ZipEntry> entries = zipFile.entries();
while (entries.hasMoreElements()) {
ZipEntry ze = (ZipEntry) entries.nextElement();
if(ze.getName().equals("gre"+File.separator+"ext.yml")){
Yaml yaml = new Yaml();
InputStream is = zipFile.getInputStream(ze);
Map<?, ?> map = (Map<?, ?>) yaml.load(is);
fullyQualifiedName = (String) map.get("main");
plname = (String) map.get("name");
plversion = (String) map.get("version");
}
}
zipFile.close();
Log.Info("Enabling "+plname+" "+plversion+" ...");
URLClassLoader classLoader = URLClassLoader.newInstance(new URL[] { new URL("file:"+file) });
Class<?> clazz = classLoader.loadClass(fullyQualifiedName);
GRPlugin pl = (GRPlugin) clazz.newInstance();
pl.enable();
Log.Info("Enabling "+plname+" "+plversion+" ...");
}else {
//skip folders
continue;
}
}
return plugins;
}
}
And the Main class of the plugin (the class extending GRPlugin) / Main.java
package io.github.plutos;
import io.github.grengine.Log;
import io.github.grengine.core.plugins.GRPlugin;
public class Main extends GRPlugin{
@Override
public void enable() {
Log.Info("ENABLED");
}
@Override
public void disable() {
Log.Info("DISABLED");
}
}
Here is the stacktrace:
java.lang.NoClassDefFoundError: io/github/grengine/core/plugins/GRPlugin
at java.lang.ClassLoader.defineClass1(Native Method) ~[?:1.8.0_05]
at java.lang.ClassLoader.defineClass(ClassLoader.java:760) ~[?:1.8.0_05]
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142) ~[?:1.8.0_05]
at java.net.URLClassLoader.defineClass(URLClassLoader.java:455) ~[?:1.8.0_05]
at java.net.URLClassLoader.access$100(URLClassLoader.java:73) ~[?:1.8.0_05]
at java.net.URLClassLoader$1.run(URLClassLoader.java:367) ~[?:1.8.0_05]
at java.net.URLClassLoader$1.run(URLClassLoader.java:361) ~[?:1.8.0_05]
at java.security.AccessController.doPrivileged(Native Method) ~[?:1.8.0_05]
at java.net.URLClassLoader.findClass(URLClassLoader.java:360) ~[?:1.8.0_05]
at java.lang.ClassLoader.loadClass(ClassLoader.java:424) ~[?:1.8.0_05]
at java.net.FactoryURLClassLoader.loadClass(URLClassLoader.java:798) ~[?:1.8.0_05]
at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[?:1.8.0_05]
at io.github.grengine.core.plugins.GRPluginManager.loadPlugins(GRPluginManager.java:82) ~[?:?]
at io.github.grengine.Main.onEnable(Main.java:56) ~[?:?]
at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:321) ~[spigot-core.jar:git-Spigot-c5146ba-c637b93]
at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:340) [spigot-core.jar:git-Spigot-c5146ba-c637b93]
at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:405) [spigot-core.jar:git-Spigot-c5146ba-c637b93]
at org.bukkit.craftbukkit.v1_8_R3.CraftServer.loadPlugin(CraftServer.java:356) [spigot-core.jar:git-Spigot-c5146ba-c637b93]
at org.bukkit.craftbukkit.v1_8_R3.CraftServer.enablePlugins(CraftServer.java:316) [spigot-core.jar:git-Spigot-c5146ba-c637b93]
at net.minecraft.server.v1_8_R3.MinecraftServer.s(MinecraftServer.java:418) [spigot-core.jar:git-Spigot-c5146ba-c637b93]
at net.minecraft.server.v1_8_R3.MinecraftServer.k(MinecraftServer.java:382) [spigot-core.jar:git-Spigot-c5146ba-c637b93]
at net.minecraft.server.v1_8_R3.MinecraftServer.a(MinecraftServer.java:337) [spigot-core.jar:git-Spigot-c5146ba-c637b93]
at net.minecraft.server.v1_8_R3.DedicatedServer.init(DedicatedServer.java:256) [spigot-core.jar:git-Spigot-c5146ba-c637b93]
at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:528) [spigot-core.jar:git-Spigot-c5146ba-c637b93]
at java.lang.Thread.run(Thread.java:745) [?:1.8.0_05]
Caused by: java.lang.ClassNotFoundException: io.github.grengine.core.plugins.GRPlugin
at java.net.URLClassLoader$1.run(URLClassLoader.java:372) ~[?:1.8.0_05]
at java.net.URLClassLoader$1.run(URLClassLoader.java:361) ~[?:1.8.0_05]
at java.security.AccessController.doPrivileged(Native Method) ~[?:1.8.0_05]
at java.net.URLClassLoader.findClass(URLClassLoader.java:360) ~[?:1.8.0_05]
at java.lang.ClassLoader.loadClass(ClassLoader.java:424) ~[?:1.8.0_05]
at java.net.FactoryURLClassLoader.loadClass(URLClassLoader.java:798) ~[?:1.8.0_05]
at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[?:1.8.0_05]
... 25 more
I just can't find a solution for this problem, I already tried different ClassLoaders (ClassLoader.getSystemClassLoader() and GRPlugin.class.getClassLoader()) ...
Can you tell what i am doing wrong? If you need more information, feel free to ask!
Thanks in advance, fusionlightcat
If you don't set a parent classloader to your custom classloader, the system classloader will be used as parent by default.
It seems that in your environment GRPlugin is loaded by a descendant of the system classloader and hence the error.
Use this instead:
URLClassLoader classLoader = URLClassLoader.newInstance(new URL[] { new URL("file:"+file) }, GRPlugin.class.getClassLoader());