private void createDirs(Path spoolerPath) {
        processingPath = createDir(spoolerPath.resolve("processing"));
        readyPath = createDir(spoolerPath.resolve("ready"));
        failuresPath = createDir(spoolerPath.resolve("failures"));
        successesPath = createDir(spoolerPath.resolve("successes"));
    }
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