转自:
http://blog.csdn.net/linghu_java/article/details/17123057
ScheduledThreadPoolExecutor介绍:
http://hubingforever.blog.163.com/blog/static/17104057920109643632988/
ThreadPoolExecutor介绍:
http://hubingforever.blog.163.com/blog/static/1710405792010964339151/