add javadoc for registry and optimize code

* code optimization
* useless import
* optimization

code optimization

Add javadoc for dubbo-serialization module(apache#3002).

* optimize log output

* Separate logs for reconnect and close

* remove reconnect exception log

* modify some log describe

* use java8 lambda expression

* fix telnet trace times is always 1

* use StringUtils determine if the string is empty

* Fix 3105 , make invoke command with Json string parameter without "class" key

* Fix 3105 ，Keep the class key to support overloaded methods

* optimize InvokerTelnetHandlerTest

* upgrade junit to junit5

* modify test

* 批量修改upgrade_junt_to_junit5

* 删除多余的文件

* fi test case

* Disabled soem test case temporarily

* upgrade junit to junit5 and batch modify test case

* copy some code from jupiter5.4.0.M1 for some issues

* 修改rat福泽

* update rat path

* revert case

* add junit-platform-surefire-provider to maven-surefire-plugin

* update dependency

* fix coverage issue (#1)

* use jupiter 5.4.0-M1 and remove junit5 source code

)

…backService method issue. (apache#3199)

* Optimize the code: fix url to null, NullPointerException, change private variable to camel mode.
* Optimize the code: exportOrUnexportCallbackService method camel mode.
* Optimize the code: fix method:encodeInvocationArgument private callbackStatus is camel writing.
* Optimize the code: fix name issue
* Exporter is a noun, we should use a verb here, like Export.
* The generics that can be inferred automatically are also deleted.

* refactor telnet invoke command

* add select command for telnet

* fix test case

…w method to replace. (apache#3232)

* keep TagRouter consistent with 2.6.x

* refactor filterUsingStaticTag using lambda in tagRouter

* wrong event setting

* modify event seeting

* modify

* Code optimization, call the util method

* mofidy

* modify *

* import package

* qos heart question fix apache#3165

* modify

* judge if it's a IdleStateEvent

* add UT

* modify

…n from dubbo.jar in shading mode , and change to dependency way.

* just for modify comments and imports

* remove gson from dubbo.jar in shading mode, add dependency

…esponsible for provide priority. (apache#3240)

something is waiting for us to disscuss:
1. Every Route implement should set a priority?
2.apache#3249

add default method into Protocol .

* modify some typos

* fix some other addionalParameterKeys and paramter typos

* Merge 2.6.6 source code into 2.7

* Fixed logging level for apache#3241 (comment)

* Change the implementation for apache#3241

* Remove the implementation Ordered, because it does not work in Spring Framework : apache#3241

* Remove the implementation Ordered, because it does not work in Spring Framework : apache#3241

* Only Optimize Imports

* fix when qos is disable,log will print every time.

* change qos server boos thread number 1

* add openjdk to travis

* add openjdk to travis

* add metrics integration

* add license

… MethodConfig.

Fixes apache#2045

…on with registry.

Fixes apache#3288

…to work. (apache#3659)

* Minor refactor, no functinoal change.

* Separate ConnectionStateListener

* Simplify code

* Fix typo

* Support get external config from etcd config center

* Polish diamond operator

* Initial etcd support as config center

* Add a put interface for JEtcdClient

* Enhanced Etcd config center support with the ability to watch and cancel watch

* Polish code

* Distinguish modification event and delete event

* Add etcd registry and configcenter to dubbo-all

* Watch again when connection is re-established

It looks good.

)