Importing and using Java Libraries in lib-custom results in NoClassDefFoundError in 1.18

Hello,

after rigorously trying to fix the issue and comparing self-built 1.17 and 1.18 server and plugin jars, it seems to strongly indicate that importing jar libraries into Jython does not seem to work. I have tried multiple libaries; ones, that can not possible have been broken by the upgrade to 1.18, but it always results in the same error.

E.g. putting the PlayerBorderAPI into /plugins and /lib-custom, and running the following code

from com.github.zandy.playerborderapi.api import PlayerBorderAPI

results in this being shown:

[20:57:47] [Server thread/WARN]: Traceback (most recent call last):
[20:57:47] [Server thread/WARN]:   File "C:\Users\Administrator\Desktop\Work In Progress Project\paper 1.18.2\.\python-plugins\pluginloader.py", line 154, in <module>
[20:57:47] [Server thread/WARN]:     loadPlugins()
[20:57:47] [Server thread/WARN]:   File "C:\Users\Administrator\Desktop\Work In Progress Project\paper 1.18.2\.\python-plugins\pluginloader.py", line 115, in loadPlugins
[20:57:47] [Server thread/WARN]:     loadPlugin(filename[:-3], [], loaded_plugins)
[20:57:47] [Server thread/WARN]:   File "C:\Users\Administrator\Desktop\Work In Progress Project\paper 1.18.2\.\python-plugins\pluginloader.py", line 115, in loadPlugins
[20:57:47] [Server thread/WARN]:     loadPlugin(filename[:-3], [], loaded_plugins)
[20:57:47] [Server thread/WARN]:   File "C:\Users\Administrator\Desktop\Work In Progress Project\paper 1.18.2\.\python-plugins\pluginloader.py", line 79, in loadPlugin
[20:57:47] [Server thread/WARN]:     execfile(pluginname + ".py", globals())
[20:57:47] [Server thread/WARN]:   File "socialscoreboard.py", line 224, in <module>
[20:57:47] [Server thread/WARN]:     from com.github.zandy.playerborderapi.api import PlayerBorderAPI
[20:57:47] [Server thread/WARN]: java.lang.NoClassDefFoundError: org/bukkit/plugin/Plugin
[20:57:47] [Server thread/WARN]:        at java.base/java.lang.Class.forName0(Native Method)
[20:57:47] [Server thread/WARN]:        at java.base/java.lang.Class.forName(Class.java:467)
[20:57:47] [Server thread/WARN]:        at org.python.core.Py.loadAndInitClass(Py.java:1160)
[20:57:47] [Server thread/WARN]:        at org.python.core.Py.findClassInternal(Py.java:1095)
[20:57:47] [Server thread/WARN]:        at org.python.core.Py.findClassEx(Py.java:1147)
[20:57:47] [Server thread/WARN]:        at org.python.core.packagecache.SysPackageManager.findClass(SysPackageManager.java:233)
[20:57:47] [Server thread/WARN]:        at org.python.core.packagecache.PackageManager.findClass(PackageManager.java:36)
[20:57:47] [Server thread/WARN]:        at org.python.core.packagecache.SysPackageManager.findClass(SysPackageManager.java:221)
[20:57:47] [Server thread/WARN]:        at org.python.core.PyJavaPackage.__findattr_ex__(PyJavaPackage.java:137)
[20:57:47] [Server thread/WARN]:        at org.python.core.PyObject.__findattr__(PyObject.java:902)
[20:57:47] [Server thread/WARN]:        at org.python.core.PyObject.__findattr__(PyObject.java:889)
[20:57:47] [Server thread/WARN]:        at org.python.core.imp.ensureFromList(imp.java:1484)
[20:57:47] [Server thread/WARN]:        at org.python.core.imp.ensureFromList(imp.java:1449)
[20:57:47] [Server thread/WARN]:        at org.python.core.imp.import_module_level(imp.java:1377)
[20:57:47] [Server thread/WARN]:        at org.python.core.imp.importName(imp.java:1528)
[20:57:47] [Server thread/WARN]:        at org.python.core.ImportFunction.__call__(__builtin__.java:1285)
[20:57:47] [Server thread/WARN]:        at org.python.core.PyObject.__call__(PyObject.java:433)
[20:57:47] [Server thread/WARN]:        at org.python.core.__builtin__.__import__(__builtin__.java:1232)
[20:57:47] [Server thread/WARN]:        at org.python.core.imp.importFromAs(imp.java:1620)
[20:57:47] [Server thread/WARN]:        at org.python.core.imp.importFrom(imp.java:1595)
[20:57:47] [Server thread/WARN]:        at org.python.pycode._pyx4.f$0(socialscoreboard.py:271)
[20:57:47] [Server thread/WARN]:        at org.python.pycode._pyx4.call_function(socialscoreboard.py)
[20:57:47] [Server thread/WARN]:        at org.python.core.PyTableCode.call(PyTableCode.java:173)
[20:57:47] [Server thread/WARN]:        at org.python.core.PyCode.call(PyCode.java:18)
[20:57:47] [Server thread/WARN]:        at org.python.core.Py.runCode(Py.java:1687)
[20:57:47] [Server thread/WARN]:        at org.python.core.__builtin__.execfile_flags(__builtin__.java:535)
[20:57:47] [Server thread/WARN]:        at org.python.core.__builtin__.execfile(__builtin__.java:512)
[20:57:47] [Server thread/WARN]:        at org.python.core.__builtin__.execfile(__builtin__.java:539)
[20:57:47] [Server thread/WARN]:        at org.python.core.BuiltinFunctions.__call__(__builtin__.java:144)
[20:57:47] [Server thread/WARN]:        at org.python.core.PyObject.__call__(PyObject.java:481)
[20:57:47] [Server thread/WARN]:        at org.python.pycode._pyx0.loadPlugin$7(C:/Users/Administrator/Desktop/Work In Progress Project/paper 1.18.2/./python-plugins/pluginloader.py:93)
[20:57:47] [Server thread/WARN]:        at org.python.pycode._pyx0.call_function(C:/Users/Administrator/Desktop/Work In Progress Project/paper 1.18.2/./python-plugins/pluginloader.py)
[20:57:47] [Server thread/WARN]:        at org.python.core.PyTableCode.call(PyTableCode.java:173)
[20:57:47] [Server thread/WARN]:        at org.python.core.PyBaseCode.call(PyBaseCode.java:168)
[20:57:47] [Server thread/WARN]:        at org.python.core.PyFunction.__call__(PyFunction.java:437)
[20:57:47] [Server thread/WARN]:        at org.python.pycode._pyx0.loadPlugins$10(C:/Users/Administrator/Desktop/Work In Progress Project/paper 1.18.2/./python-plugins/pluginloader.py:140)
[20:57:47] [Server thread/WARN]:        at org.python.pycode._pyx0.call_function(C:/Users/Administrator/Desktop/Work In Progress Project/paper 1.18.2/./python-plugins/pluginloader.py)
[20:57:47] [Server thread/WARN]:        at org.python.core.PyTableCode.call(PyTableCode.java:173)
[20:57:47] [Server thread/WARN]:        at org.python.core.PyBaseCode.call(PyBaseCode.java:119)
[20:57:47] [Server thread/WARN]:        at org.python.core.PyFunction.__call__(PyFunction.java:406)
[20:57:47] [Server thread/WARN]:        at org.python.pycode._pyx0.f$0(C:/Users/Administrator/Desktop/Work In Progress Project/paper 1.18.2/./python-plugins/pluginloader.py:156)
[20:57:47] [Server thread/WARN]:        at org.python.pycode._pyx0.call_function(C:/Users/Administrator/Desktop/Work In Progress Project/paper 1.18.2/./python-plugins/pluginloader.py)
[20:57:47] [Server thread/WARN]:        at org.python.core.PyTableCode.call(PyTableCode.java:173)
[20:57:47] [Server thread/WARN]:        at org.python.core.PyCode.call(PyCode.java:18)
[20:57:47] [Server thread/WARN]:        at org.python.core.Py.runCode(Py.java:1687)
[20:57:47] [Server thread/WARN]:        at org.python.core.__builtin__.execfile_flags(__builtin__.java:535)
[20:57:47] [Server thread/WARN]:        at org.python.util.PythonInterpreter.execfile(PythonInterpreter.java:287)
[20:57:47] [Server thread/WARN]:        at com.macuyiko.minecraftpyserver.jython.JyInterpreter.execfile(JyInterpreter.java:128)
[20:57:47] [Server thread/WARN]:        at com.macuyiko.minecraftpyserver.MinecraftPyServerPlugin.startPluginInterpreters(MinecraftPyServerPlugin.java:123)
[20:57:47] [Server thread/WARN]:        at com.macuyiko.minecraftpyserver.MinecraftPyServerPlugin.onEnable(MinecraftPyServerPlugin.java:58)
[20:57:47] [Server thread/WARN]:        at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:264)
[20:57:47] [Server thread/WARN]:        at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:342)
[20:57:47] [Server thread/WARN]:        at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:480)
[20:57:47] [Server thread/WARN]:        at org.bukkit.craftbukkit.v1_18_R2.CraftServer.enablePlugin(CraftServer.java:518)
[20:57:47] [Server thread/WARN]:        at org.bukkit.craftbukkit.v1_18_R2.CraftServer.enablePlugins(CraftServer.java:432)
[20:57:47] [Server thread/WARN]:        at net.minecraft.server.MinecraftServer.loadWorld0(MinecraftServer.java:612)
[20:57:47] [Server thread/WARN]:        at net.minecraft.server.MinecraftServer.loadLevel(MinecraftServer.java:414)
[20:57:47] [Server thread/WARN]:        at net.minecraft.server.dedicated.DedicatedServer.e(DedicatedServer.java:263)
[20:57:47] [Server thread/WARN]:        at net.minecraft.server.MinecraftServer.w(MinecraftServer.java:1007)
[20:57:47] [Server thread/WARN]:        at net.minecraft.server.MinecraftServer.lambda$0(MinecraftServer.java:304)
[20:57:47] [Server thread/WARN]:        at java.base/java.lang.Thread.run(Thread.java:833)
[20:57:47] [Server thread/WARN]: Caused by: java.lang.ClassNotFoundException: org.bukkit.plugin.Plugin
[20:57:47] [Server thread/WARN]:        at java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:445)
[20:57:47] [Server thread/WARN]:        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:587)
[20:57:47] [Server thread/WARN]:        at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520)
[20:57:47] [Server thread/WARN]:        ... 61 more
[20:57:47] [Server thread/WARN]: java.lang.NoClassDefFoundError: java.lang.NoClassDefFoundError: org/bukkit/plugin/Plugin

From this post it seems, that in Java 17 the way Reflections work has changed. Though I have not looked into how this plugin functions, but maybe that could be a hint?

[Macuyiko]

Should be fixed in the latest release. Reflections and JDK 17+ was already fixed previously. The problem was due to the way how Spigot now handles its own JARs/libraries.

[MuffinMario]

For now, it seems that everything is working. Thank you for your quick responses and cooperation!