Optimize code of sentinel-plugin

[6freeair2016]

Optimize code of sentinel-plugin【issueNo: 4668】

Make sure that:

• [✔] You have read the contribution guidelines.
• [✔ ] You submit test cases (unit or integration tests) that back your changes.
• [✔ ] Your local test passed ./mvnw clean install -Dmaven.javadoc.skip=true.

[codecov-commenter]

Codecov Report

Merging #4669 (c2f9fdf) into master (f3aa857) will decrease coverage by 0.01%.
The diff coverage is 66.66%.

@@             Coverage Diff              @@
##             master    #4669      +/-   ##
============================================
- Coverage     66.93%   66.92%   -0.01%     
+ Complexity     8006     8005       -1     
============================================
  Files          1099     1099              
  Lines         31758    31758              
  Branches       2874     2874              
============================================
- Hits          21257    21255       -2     
- Misses         8824     8827       +3     
+ Partials       1677     1676       -1     

Impacted Files	Coverage Δ
...a/org/apache/shenyu/common/constant/Constants.java	83.33% <ø> (ø)
...shenyu/common/dto/convert/rule/SentinelHandle.java	80.26% <50.00%> (ø)
.../apache/shenyu/plugin/sentinel/SentinelPlugin.java	63.15% <100.00%> (ø)
...yu/plugin/sentinel/handler/SentinelRuleHandle.java	80.39% <100.00%> (ø)

... and 3 files with indirect coverage changes

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