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我目前正在爲Java程序製作一個小插件框架。 基本上GRPluginManager.loadPlugins()循環遍歷目錄中的所有jar文件，然後從jar內的特定文件讀取此插件的Main-class的名稱，並將其加載到類路徑中。之後，它調用這個插件 - Main-class的enable()方法（它擴展了GRPlugin）。Java類加載導致父類的ClassNotFoundException
但是，它不起作用。它看起來像插件主類的加載正常工作，只有父類（GRPlugin）無法找到。但它絕對存在。
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;
}
}
和主類的插件（類延伸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");
}
}
這裏是堆棧跟蹤：
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
我無法找到一個解決這個問題，我已經嘗試過不同的類加載器（ClassLoader.getSystemClassLoader()和GRPlugin.class.getClassLoader()）...
你能告訴我是什麼做錯了？如果您需要更多信息，請隨時詢問！
由於提前， fusionlightcat
這解決了它，+1爲好的解釋！ – fusionlightcat
很高興幫助！ – idelvall