polish code and fix (#3761)

[chenlushun]

polish code and add javadoc

[codecov-io]

Codecov Report

Merging #3838 into master will decrease coverage by 0.02%.
The diff coverage is 76.47%.

@@             Coverage Diff              @@
##             master    #3838      +/-   ##
============================================
- Coverage      63.6%   63.57%   -0.03%     
  Complexity       71       71              
============================================
  Files           708      708              
  Lines         31192    31191       -1     
  Branches       5048     5048              
============================================
- Hits          19839    19831       -8     
- Misses         9072     9081       +9     
+ Partials       2281     2279       -2

Impacted Files	Coverage Δ	Complexity Δ
.../org/apache/dubbo/cache/support/jcache/JCache.java	86.95% <ø> (ø)	0 <0> (ø)	⬇️
...data/definition/builder/CollectionTypeBuilder.java	47.61% <ø> (ø)	4 <0> (ø)	⬇️
...api/src/main/java/org/apache/dubbo/rpc/Filter.java	100% <ø> (ø)	0 <0> (ø)	⬇️
...bo/metadata/definition/model/MethodDefinition.java	39.28% <0%> (ø)	8 <0> (ø)	⬇️
...bo/metadata/definition/builder/MapTypeBuilder.java	47.61% <0%> (ø)	5 <0> (ø)	⬇️
...bo/cache/support/threadlocal/ThreadLocalCache.java	100% <100%> (ø)	0 <0> (ø)	⬇️
...he/dubbo/cache/support/expiring/ExpiringCache.java	100% <100%> (ø)	0 <0> (ø)	⬇️
...o/metadata/definition/builder/EnumTypeBuilder.java	75% <100%> (ø)	4 <0> (ø)	⬇️
...bbo/validation/support/jvalidation/JValidator.java	79.87% <100%> (ø)	0 <0> (ø)	⬇️
...ache/dubbo/cache/support/expiring/ExpiringMap.java	40.35% <100%> (ø)	0 <0> (ø)	⬇️
... and 18 more

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[ralf0131]

LGTM, thanks for the pull request.