[ISSUE 3203] Replace the class 'StringBuffer' by 'StringBuilder'

[gorden5566]

Make sure set the target branch to develop

What is the purpose of the change

1. Replace the class 'StringBuffer' by 'StringBuilder'
2. Add missed '@OverRide' annotation
3. Add braces to 'if' statement
4. Add test for UtilAll#list2String

#3203

Brief changelog

XX

Verifying this change

XXXX

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[coveralls]

Coverage increased (+0.09%) to 54.201% when pulling 366ee98 on gorden5566:optimize-string-concate into 9e8fea9 on apache:develop.

[codecov-commenter]

Codecov Report

Merging #3204 (366ee98) into develop (9e8fea9) will increase coverage by 0.01%.
The diff coverage is 37.50%.

@@              Coverage Diff              @@
##             develop    #3204      +/-   ##
=============================================
+ Coverage      48.45%   48.46%   +0.01%     
- Complexity      3185     3188       +3     
=============================================
  Files            418      418              
  Lines          26318    26318              
  Branches        3487     3487              
=============================================
+ Hits           12752    12755       +3     
+ Misses         11921    11914       -7     
- Partials        1645     1649       +4     

Impacted Files	Coverage Δ
...va/org/apache/rocketmq/common/message/Message.java	54.21% <0.00%> (ø)
...apache/rocketmq/common/protocol/NamespaceUtil.java	54.83% <0.00%> (ø)
...he/rocketmq/filter/expression/UnaryExpression.java	21.05% <0.00%> (ø)
...g/apache/rocketmq/filter/parser/TokenMgrError.java	0.00% <0.00%> (ø)
...pache/rocketmq/remoting/common/RemotingHelper.java	13.41% <0.00%> (ø)
...pache/rocketmq/store/stats/BrokerStatsManager.java	75.89% <50.00%> (ø)
.../apache/rocketmq/filter/parser/ParseException.java	49.25% <66.66%> (ø)
...cketmq/acl/plain/RemoteAddressStrategyFactory.java	89.76% <100.00%> (ø)
.../main/java/org/apache/rocketmq/common/UtilAll.java	40.25% <100.00%> (+2.59%)	⬆️
...ache/rocketmq/store/AllocateMappedFileService.java	39.02% <0.00%> (-2.44%)	⬇️
... and 7 more

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