[DISCUSS] Improve code quality

[Lamber-Ken]

Dear community,

I noticed that there is a lot of work to improve code quality.

e.g
1. Not enough arguments.
  LOG.warn("Exception when reading header of {} : {}", lf, buf);
2. Optional.
  java.util.Optional and com.google.common.base.Optional can be merged.
3. @Slf4j
  @Slf4j / LoggerFactory.getLogger(xxx.class);
..

We can use some tools to check them, then fix them manually or automatically, 
any thoughts?


Thanks,
Lamber-Ken