private BatchWriterPlusException getWriter(String writer) throws UnknownWriter {
UUID uuid = null;
try {
uuid = UUID.fromString(writer);
} catch (IllegalArgumentException iae) {
throw new UnknownWriter(iae.getMessage());
}
BatchWriterPlusException bwpe = writerCache.getIfPresent(uuid);
if (bwpe == null) {
throw new UnknownWriter("Writer never existed or no longer exists");
}
return bwpe;
}