转自：
http://www.coderanch.com/t/508779/ORM/java/Ehcache-TimeToLiveSecond-TimeToIdleSeconds
timeToLiveSecond is the time in seconds from the point of creation in the cache till it expires (regardless of how frequently it is accessed in that time)
timeToIdleSeconds is the time in seconds before an object in the cache expires if it is not accessed.