refactor

[wenshao]

What this PR does / why we need it?

Summary of your change

Please indicate you've done the following:

• Made sure tests are passing and test coverage is added if needed.
• Made sure commit message follow the rule of Conventional Commits specification.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 93.02832% with 32 lines in your changes missing coverage. Please review.

Project coverage is 74.12%. Comparing base (714a2b6) to head (18124b8).

Files with missing lines	Patch %	Lines
...ain/java/com/alibaba/fastjson2/JSONWriterUTF8.java	91.82%	20 Missing and 2 partials ⚠️
...in/java/com/alibaba/fastjson2/JSONWriterJSONB.java	94.41%	5 Missing and 5 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #3294      +/-   ##
============================================
- Coverage     74.15%   74.12%   -0.03%     
+ Complexity    23326    23283      -43     
============================================
  Files           668      668              
  Lines         89315    89013     -302     
  Branches      20224    20163      -61     
============================================
- Hits          66228    65984     -244     
+ Misses        14927    14892      -35     
+ Partials       8160     8137      -23     

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