Konloch/bytecode-viewer · error · RuntimeException

Multiple plugin subclasses.

Error message

Multiple plugin subclasses.

What it means

CompiledJavaPluginLaunchStrategy.run loads classes from the compiled plugin bundle and scans ClassNodes for exactly one subclass of Plugin (PLUGIN_CLASS_NAME). If two or more classes extend Plugin it cannot pick which to instantiate and throws RuntimeException("Multiple plugin subclasses.").

Source

Thrown at src/main/java/the/bytecode/club/bytecodeviewer/plugin/strategies/CompiledJavaPluginLaunchStrategy.java:61

    private static final String PLUGIN_CLASS_NAME = Plugin.class.getCanonicalName().replace(".", "/");

    private final Set<LoadedPluginData> loaded = new HashSet<>();

    @Override
    public Plugin run(File file) throws Throwable
    {
        Set<LoadedNodeData> set = loadData(file);

        LoadedNodeData pdata = null;
        for (LoadedNodeData d : set)
        {
            ClassNode cn = d.node;
            if (Objects.equals(cn.superName, PLUGIN_CLASS_NAME))
            {
                if (pdata == null)
                    pdata = d;
                else
                    throw new RuntimeException("Multiple plugin subclasses.");
            }
        }

        LoadingClassLoader cl = new LoadingClassLoader(pdata, set);
        Plugin p = cl.pluginKlass.getDeclaredConstructor().newInstance();
        LoadedPluginData npdata = new LoadedPluginData(pdata, cl, p);
        loaded.add(npdata);

        return p;
    }

    public Set<LoadedPluginData> getLoaded()
    {
        return loaded;
    }

    private static Set<LoadedNodeData> loadData(File jarFile) throws Throwable
    {

View on GitHub (pinned to 31430e0033)

Solutions

1. Ensure exactly one class extends Plugin in the plugin bundle; remove or split the others.
2. Clean the build output and recompile so stale classes are not bundled.
3. Split each plugin class into its own plugin file and run them separately.
4. Convert extra classes to not extend Plugin (use plain helpers).

Example fix

// before
class MyPlugin extends Plugin { ... }
class MyOtherPlugin extends Plugin { ... } // bundled together -> throws
// after
class MyPlugin extends Plugin { ... }
class MyHelper { ... } // only one Plugin subclass in the bundle

try {
    PluginManager.runPlugin(compiledPluginFile);
} catch (RuntimeException e) {
    if ("Multiple plugin subclasses.".equals(e.getMessage()))
        showError("Bundle contains more than one Plugin subclass; split or clean the plugin.");
    else
        throw e;
}

When it happens

Trigger: Running a compiled Java plugin whose class set contains two or more classes whose superName equals PLUGIN_CLASS_NAME — e.g. several plugin classes bundled into one plugin file.

Common situations: Bundling multiple plugins into a single compiled plugin archive; leftover old plugin classes not removed from the build; an inner/helper class accidentally extending Plugin; recompiling into the same output directory merging old classes.

Related errors

• Cannot find Groovy script engine! Please contact Konloch.
• Invalid internal class name
• No launch strategy for extension %s (%s)
• Cannot find Javascript script engine! Please contact Konloch
• Cannot find Jython script engine! Please contact Konloch.

AI-assisted analysis of Konloch/bytecode-viewer@31430e0033 (2026-09-05). Data as JSON: /api/errors/7ce9e42d835981e4. Report an issue: GitHub.