[Suggestion] Add checkstyle for CI

[htynkn]

hey team,

I notice there is some unused code (for example: https://github.com/apache/incubator-dubbo/blob/master/hessian-lite/src/main/java/com/alibaba/com/caucho/hessian/io/Hessian2Input.java#L88)

Looks like dubbo doesn't have checkstyle in maven configuration or it doesn't have correct rule.

do we have any plan to add checkstyle check in CI?

[ralf0131]

Strongly +1. Static analysis might produce false positives, but overall I think it is better than not having it.

[ralf0131]

Suggestions are expected to be reported to the mailing list dev@incubator.dubbo.apache.org. Issues are used to track bugs.

[htynkn]

@ralf0131 sure thing. next time I will send suggestion to maillist

[justinmclean]

Apache runs SonarQube if you want to use that. See https://builds.apache.org/analysis/

[htynkn]

I did a quick try. I only apply one basic rule.
According to dubbo code-conventions.

If there are more than 120 characters in current line, start a new line.

Checkstyle find more than 6000 Checkstyle violations :(