@Override
    public void put(Collection<SinkRecord> sinkRecords) {
        for (SinkRecord record : sinkRecords) {
            log.trace("Writing line to {}: {}", logFilename(), record.value());
            outputStream.println(record.value());
        }
    }
FileStreamSinkTask writes records to stdout or a file.
connect/file/src/main/java/org/apache/kafka/connect/file/FileStreamSinkTask.java