optimize : javadoc should be used for classes, class variables and methods.

[EZKAYOTWJPRKXWCUYEEB]

Ⅰ. Describe what this PR did

Ⅱ. Does this pull request fix one issue?

Ⅲ. Why don't you add test cases (unit test/integration test)?

Ⅳ. Describe how to verify it

Ⅴ. Special notes for reviews

[codecov-io]

Codecov Report

Merging #1911 into develop will decrease coverage by 0.03%.
The diff coverage is n/a.

@@              Coverage Diff              @@
##             develop    #1911      +/-   ##
=============================================
- Coverage      55.32%   55.29%   -0.04%     
+ Complexity      2401     2400       -1     
=============================================
  Files            428      428              
  Lines          14347    14347              
  Branches        1688     1688              
=============================================
- Hits            7938     7933       -5     
- Misses          5695     5697       +2     
- Partials         714      717       +3

Impacted Files	Coverage Δ	Complexity Δ
...java/io/seata/rm/datasource/ConnectionContext.java	60% <ø> (ø)	15 <0> (ø)	⬇️
...c/main/java/io/seata/server/store/StoreConfig.java	83.33% <ø> (ø)	5 <0> (ø)	⬇️
...server/store/file/FileTransactionStoreManager.java	56.96% <0%> (-0.95%)	29% <0%> (ø)
...in/java/io/seata/server/session/GlobalSession.java	84.54% <0%> (-0.49%)	67% <0%> (-1%)
...o/seata/server/coordinator/DefaultCoordinator.java	48.01% <0%> (-0.4%)	28% <0%> (ø)

[slievrly]

LGTM

[helloworlde]

LGTM

[zjinlei]

LGTM

[jsbxyyx]

LGTM