java中线程安全的map是ConcurrentHashMap

原理：http://www.cnblogs.com/ITtangtang/p/3948786.html

与hashtable的区别：  http://blog.csdn.net/songfeihu0810232/article/details/70012260

补充：http://www.importnew.com/16142.html

map的正确删除http://blog.csdn.net/chjr1000/article/details/50358420