[Dubbo-4331] Improve api doc #4331

[sonymoon]

What is the purpose of the change

fix #4331

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[sonymoon]

This should work: ./mvnw clean javadoc:aggregate -Dmaven.javadoc.skip=false -Prelease in my local OS. Just need a profile specified and some plugin configurations.

[sonymoon]

INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  07:18 min
[INFO] Finished at: 2019-09-16T11:36:35Z
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.6.0:testCompile (default-testCompile) on project dubbo-rpc-dubbo: Compilation failure
[ERROR] error: error reading /home/travis/.m2/repository/org/glassfish/javax.el/3.0.1-b08/javax.el-3.0.1-b08.jar; error in opening zip file
[ERROR] -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoFailureException
[ERROR] 
[ERROR] After correcting the problems, you can resume the build with the command
[ERROR]   mvn <goals> -rf :dubbo-rpc-dubbo
/home/travis/.travis/functions: line 537:  4348 Terminated              travis_jigger "${!}" "${timeout}" "${cmd[@]}"
travis_time:end:06a84ff2:start=1568633355964402712,finish=1568633795937931705,duration=439973528993,event=script
�[0K�[31;1mThe command "travis_wait 30 ./mvnw --batch-mode --no-transfer-progress clean install -DskipTests=false -Dcheckstyle.skip=false -Drat.skip=false -Dmaven.javadoc.skip=true" exited with 1.�[0m

CI Failed. Not related to this PR.

[sonymoon]

Could someone re-trigger CI test ? ping @chickenlj @cvictory

[sonymoon]

I would be very appreciated if you help review @htynkn.

[codecov-io]

Codecov Report

Merging #5070 into master will decrease coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #5070      +/-   ##
============================================
- Coverage     64.01%   63.98%   -0.04%     
- Complexity      451      452       +1     
============================================
  Files           769      769              
  Lines         33246    33246              
  Branches       5246     5246              
============================================
- Hits          21284    21273      -11     
- Misses         9530     9546      +16     
+ Partials       2432     2427       -5

Impacted Files	Coverage Δ	Complexity Δ
.../apache/dubbo/qos/protocol/QosProtocolWrapper.java	65.85% <0%> (-17.08%)	0% <0%> (ø)
...ng/transport/dispatcher/all/AllChannelHandler.java	51.42% <0%> (-5.72%)	0% <0%> (ø)
...pache/dubbo/registry/support/AbstractRegistry.java	78.54% <0%> (-3.07%)	0% <0%> (ø)
.../rpc/protocol/dubbo/LazyConnectExchangeClient.java	56.47% <0%> (-2.36%)	0% <0%> (ø)
.../dubbo/remoting/transport/netty4/NettyChannel.java	64.77% <0%> (+1.13%)	0% <0%> (ø)	⬇️
...c/main/java/org/apache/dubbo/rpc/RpcException.java	83.33% <0%> (+3.33%)	0% <0%> (ø)	⬇️
...e/dubbo/remoting/transport/netty/NettyChannel.java	60.22% <0%> (+4.54%)	21% <0%> (+1%)	⬆️
...onfig/spring/extension/SpringExtensionFactory.java	85.36% <0%> (+4.87%)	0% <0%> (ø)	⬇️

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[htynkn]

What maven command should use with this change?
I try ./mvnw clean javadoc:aggregate -Dmaven.javadoc.skip=false somehow those changes can't apply to javadoc

[sonymoon]

What maven command should use with this change?
I try ./mvnw clean javadoc:aggregate -Dmaven.javadoc.skip=false somehow those changes can't apply to javadoc

./mvnw clean javadoc:aggregate -Dmaven.javadoc.skip=false -Prelease .
-P release is required because the javadoc maven plugin is configured under profile release
@htynkn

[htynkn]

Thanks for your contribution