i made one plugin, but the spark seems does not load it

i made one  plugin use the examply code, it's name is myplugin.jar, and copy to the plugins directory(D:\Program Files (x86)\Spark\plugins).

i found nothing in the spark's plugin management panel. the error.log in the logs directory is empty.

how can i make sure the plugin is active?

i use spark 2.6.3.

thanks!