Add the feature of excluding unused URLs in CommonFilter (#287)

[lym-ifae]

Why we need it

We need to support filtering urls that don't want to be resource in CommonFilter.

Does this pull request fix one issue?

Resolves #287

Describe how you did it

As there's already a UrlCleaner interface, we could just reuse the interface and improve the logic of unifying the resource name with UrlCleaner. If developers are going to exclude some URLs, they can convert the URLs to the empty string "" in their UrlCleaner implementation, and in CommonFilter we could check whether the cleaned resource name is empty. If it's empty, then it should be excluded and won't go through the logic of Sentinel SphU.entry.

Describe how to verify it

We can get the statistic node of the resource via ClusterBuilderSlot.getClusterNode(res) method, and if the ClusterNode of the target URL is absent, then we think it has been excluded.

Special notes for reviews

[CLAassistant]

All committers have signed the CLA.

[codecov-io]

Codecov Report

Merging #914 into master will decrease coverage by 0.08%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #914      +/-   ##
============================================
- Coverage     42.58%   42.49%   -0.09%     
+ Complexity     1443     1440       -3     
============================================
  Files           310      310              
  Lines          8992     8993       +1     
  Branches       1221     1222       +1     
============================================
- Hits           3829     3822       -7     
- Misses         4696     4701       +5     
- Partials        467      470       +3

Impacted Files	Coverage Δ	Complexity Δ
...aba/csp/sentinel/adapter/servlet/CommonFilter.java	75% <100%> (+0.58%)	10 <0> (+1)	⬆️
...ava/com/alibaba/csp/sentinel/node/ClusterNode.java	95.23% <0%> (-4.77%)	7% <0%> (-1%)
...a/csp/sentinel/slots/statistic/base/LeapArray.java	67.32% <0%> (-2.98%)	33% <0%> (-1%)
...tinel/slots/block/flow/param/ParamFlowChecker.java	52.7% <0%> (-2.71%)	28% <0%> (-1%)
...ain/java/com/alibaba/csp/sentinel/log/LogBase.java	56.94% <0%> (ø)	10% <0%> (ø)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 326dd44...9dec9ea. Read the comment docs.

[sczyh30]

And could you please also update the document here: https://github.com/alibaba/Sentinel/blob/master/sentinel-adapter/sentinel-web-servlet/README.md

[sczyh30]

LGTM

Found another incorrect logic

[sczyh30]

@lym-ifae The CI status indicates there's something wrong with your changes: https://travis-ci.org/alibaba/Sentinel/builds/559316648

[sczyh30]

LGTM

[sczyh30]

Thanks for contributing! 👍