FileDownloadUtils

function	description
setDefaultSaveRootPath(path:String)	The path is used as Root Path in the case of task without setting path in the entire Download Engine
getTempPath	Get the temp path is used for storing the temporary file not completed downloading yet(filename.temp)
isFilenameConverted(context:Context)	Whether tasks from FileDownloader Database has converted all files' name from filename(in old architecture) to filename.temp, if it is not completed downloading yet
generateId(url:String, path:String, pathAsDirectory:boolean)	Generate a Download Id which can be recognized in FileDownloader