Refactor

[wenshao]

减少重复代码，提升可维护性

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 90.90909% with 9 lines in your changes missing coverage. Please review.

Project coverage is 72.72%. Comparing base (eb28d51) to head (2ef1c4d).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
.../main/java/com/alibaba/fastjson2/util/IOUtils.java	75.00%	3 Missing and 2 partials ⚠️
...in/java/com/alibaba/fastjson2/JSONWriterUTF16.java	94.93%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #3275      +/-   ##
============================================
- Coverage     74.29%   72.72%   -1.58%     
+ Complexity    23451    22806     -645     
============================================
  Files           668      668              
  Lines         89915    89476     -439     
  Branches      20337    20276      -61     
============================================
- Hits          66798    65067    -1731     
- Misses        14932    16055    +1123     
- Partials       8185     8354     +169     

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