gistfile1.java

URLClassLoader loader;
try {
	loader = new URLClassLoader(new URL[] {
			file.toURI().toURL()
	}, ClassLoader.getSystemClassLoader());
} catch (Exception e) {
	log.error("can't load {} because : {}", file.getPath(), e.getMessage());
	return null;
}

InputStream is = loader.getResourceAsStream("plugin_class");
BufferedReader reader = new BufferedReader(new InputStreamReader(is));

String className;
try {
	className = reader.readLine();
} catch (IOException e) {
	log.error("can't read plugin_class file");
	try {
		loader.close();
	} catch (IOException ignored) { }
	return null;
}

Class<?> clazz;
try {
	clazz = loader.loadClass(className);
} catch (ClassNotFoundException e) {
	log.error("can't load {} class", className);
	try {
		loader.close();
	} catch (IOException ignored) { }
	return null;
}

if (!clazz.isAssignableFrom(Plugin.class)) {
	log.error("{} is not a plugin", className);
	try {
		loader.close();
	} catch (IOException ignored) { }
	return null;
}

try {
	try {
		loader.close();
	} catch (IOException ignored) { }
	return (Plugin) clazz.newInstance();
} catch (Exception e) {
	log.error("can't instantiate {} because : {}", className, e.getMessage());
}
try {
	loader.close();
} catch (IOException ignored) { }
return null;