callable
http://eyesmore.iteye.com/blog/243648#
http://blog.csdn.net/com360/article/details/6796722
http://www.cnblogs.com/uptownBoy/articles/1772483.html
executorservice
http://blog.sina.com.cn/s/blog_6151984a0100krj8.html
http://promzaid.iteye.com/blog/1408095
observable