class path and classloader
https://www.artima.com/insidejvm/ed2/linkmod5.html
https://www.artima.com/insidejvm/ed2/securityP.html
https://docs.oracle.com/javase/jndi/tutorial/beyond/misc/classloader.html
https://docstore.mik.ua/orelly/java-ent/security/ch03_01.htm
https://www.ibm.com/developerworks/cn/java/j-lo-classloader/
https://www.javaworld.com/article/2077344/core-java/find-a-way-out-of-the-classloader-maze.html
http://www.tiantianbianma.com/java-classloader-detail.html/
https://blog.csdn.net/briblue/article/details/54973413