Javassist CtClass 可以工作，但在调用构造函数时抛出 NoClassDefError

Question

当我通过反射调用无参数构造函数时，它会抛出 NoClassDefError。我确信 bukkit 加载了我项目的所有类，因为当使用 Class.forName(String) 调用类时它不会抛出异常。

如何使用此代码解析 ClassNotFound？

我使用了这段代码:

  ClassPool pool = ClassPool.getDefault();

        pool.insertClassPath(new ClassClassPath(ReflectedNBTCompound.class));
        CtClass cl = pool.getCtClass(ReflectedNBTWrapper.class.getCanonicalName());
        CtClass ct = pool.makeClass("NBTCompatibleTileEntity", ctClass);
        ct.addField(new CtField(cl, "nbtField", ct));
        ct.addConstructor(CtNewConstructor.make(
                "public NBTCompatibleTileEntity(){" +
                        " this.nbtField = new skywolf46.NBTUtil.v1_3.NBTData.ReflectedNBTCompound();" +
                        "System.out.println(\"Object created!\");" +
                        "}"

                , ct
        ));
        ct.addMethod(CtMethod.make(
                "public skywolf46.NBTUtil.v1_3.NBTData.ReflectedNBTCompound getNBT(){" +
                        "  return nbtField;" +
                        "}"
                , ct));

        ct.addMethod(CtMethod.make(
                "public void load(" + BukkitVersionUtil.getNMSClass("NBTTagCompound").getName() + " comp){" +
                        "  if(comp.hasKey(\"ReflectedNBT\"))" +
                        "    nbtField = new skywolf46.NBTUtil.v1_3.NBTData.ReflectedNBTCompound(comp.getCompound(\"ReflectedNBT\"));" +
                        "}"
                , ct));
        Class c = ct.toClass();
        c.getConstructor().newInstance();
        Bukkit.getConsoleSender().sendMessage("§5ReflectedNBTWrapper §7| §aInitialized! ");

错误:

java.lang.NoClassDefFoundError: skywolf46/NBTUtil/v1_3/NBTData/ReflectedNBTCompound
        at java.lang.Class.getDeclaredConstructors0(Native Method) ~[?:1.8.0_202]
        at java.lang.Class.privateGetDeclaredConstructors(Class.java:2671) ~[?:1.8.0_202]
        at java.lang.Class.getConstructor0(Class.java:3075) ~[?:1.8.0_202]
        at java.lang.Class.getConstructor(Class.java:1825) ~[?:1.8.0_202]
        at skywolf46.NBTUtil.v1_3.ReflectedNBTWrapper.initBukkit(ReflectedNBTWrapper.java:88) ~[?:?]
        at skywolf46.NBTUtil.v1_3.ReflectedNBTWrapper.onEnable(ReflectedNBTWrapper.java:27) ~[?:?]
        at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:264) ~[spigot-ram-patched.jar:git-Spigot-79a30d7-acbc348]
        at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:337) [spigot-ram-patched.jar:git-Spigot-79a30d7-acbc348]
        at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:403) [spigot-ram-patched.jar:git-Spigot-79a30d7-acbc348]
        at org.bukkit.craftbukkit.v1_12_R1.CraftServer.enablePlugin(CraftServer.java:381) [spigot-ram-patched.jar:git-Spigot-79a30d7-acbc348]
        at org.bukkit.craftbukkit.v1_12_R1.CraftServer.enablePlugins(CraftServer.java:330) [spigot-ram-patched.jar:git-Spigot-79a30d7-acbc348]
        at net.minecraft.server.v1_12_R1.MinecraftServer.t(MinecraftServer.java:422) [spigot-ram-patched.jar:git-Spigot-79a30d7-acbc348]
        at net.minecraft.server.v1_12_R1.MinecraftServer.l(MinecraftServer.java:383) [spigot-ram-patched.jar:git-Spigot-79a30d7-acbc348]
        at net.minecraft.server.v1_12_R1.MinecraftServer.a(MinecraftServer.java:338) [spigot-ram-patched.jar:git-Spigot-79a30d7-acbc348]
        at net.minecraft.server.v1_12_R1.DedicatedServer.init(DedicatedServer.java:272) [spigot-ram-patched.jar:git-Spigot-79a30d7-acbc348]
        at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:545) [spigot-ram-patched.jar:git-Spigot-79a30d7-acbc348]
        at java.lang.Thread.run(Thread.java:748) [?:1.8.0_202]
Caused by: java.lang.ClassNotFoundException: skywolf46.NBTUtil.v1_3.NBTData.ReflectedNBTCompound
        at java.net.URLClassLoader.findClass(URLClassLoader.java:382) ~[?:1.8.0_202]
        at java.lang.ClassLoader.loadClass(ClassLoader.java:424) ~[?:1.8.0_202]
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349) ~[?:1.8.0_202]
        at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[?:1.8.0_202]

Answer 1

您可能在错误的类加载器中定义了此类，在 bukkit 中，每个插件都位于单独的类加载器中，并且 .toClass() 使用线程上下文类加载器，该类加载器可能设置为某个不同的类加载器.
因此，当加载新类时，它会尝试从插件中查找其他类，但会失败，因为无法从此类加载器访问它们。

尝试使用

Class c = ct.toClass(ReflectedNBTCompound.class)

或

Class c = ct.toClass(MyPlugin.class.getClassLoader())