基于平面文件的Java内存读/写缓存

I have a flat file which consists of a list of device identifiers. When my Java/tomcat based application receives a request from a particular device, it decides the business logic based on presence of the device identifier in the file (The device identifier MAY or MAY NOT be there in the file even though the device exists). Also, there are use cases when I have a flat file which consists of a list of