public int compare(File a, File b) {
            return (int) (a.lastModified() - b.lastModified());
        }
Spooler that will write an entry to a file and read files that are ready to be sent.
Files are written in JSON Lines text file format.

@author hmusum
container-search/src/main/java/com/yahoo/search/logging/Spooler.java