* add cassandra java driver 3.x plugin

* add logstash logback plugin

* add logstash logback plugin, set pom provided, refine logback doc

* refine logstash logback doc

* refine the comment

* remove the app_id that not related to SkyWalking

* remove tag @date for CI error: unknown tag: date

* add description for iLoggingEvent for ci warning: no description for @param

* Fix the zookeeper plugin has many nodes in the cluster case

* support version

* Support play 2.x 

* ADD: add operationName length threshold

* MOD:move operationName threshold to Config, simplified code

* MOD:update agent set-up document, clean code

* MOD:add agent.operation_name_threshold conf prefix

* Support op group name in agent config core.

* Provide core API for operation name grouping, rest template plugin update, and doc update.

* Fix doc

* Fix test case.

* Fix missing changes.

* add shuyun to powered-by.md (#3341)

* add shuyun to powered-by.md

* update powered-by.md

* Remove static method.

* Log4j2 support AsyncRoot print tid
Support AsyncRoot print tid of all versions of log4j2 2.1+

* Add pattern logger to replace the easy logger.
* Doc update
* Support console log 

change `agent.span_limit_per_segment` default value to match the default value of `SPAN_LIMIT_PER_SEGMENT` in https://github.com/apache/skywalking/blob/master/apm-sniffer/apm-agent-core/src/main/java/org/apache/skywalking/apm/agent/core/conf/Config.java

* improve auto connect

* add config

* use int instread of atomic

* update format

* update doc

* update var name and doc

* fix

* add http

* update plugin

* Add StaticMethodsAroundInterceptor to be injected.

* move to options plugin

* move folder

* update pom

* support https

* add witness class

* Make JDK9-11 available for bootstrap instrumentation

* Remove temp folder of old bootstrap instrumentation requirement.

* remove witness ,work for jdk6,7,8,9,10,11

* Make JDK 12 works.

* move jdk-http-plugin to bootstrap-plugins folder

* add httpsclient

* update README.md

* Support upgrade backend w/o rebooting agents

* Make JDK9-11 available for bootstrap instrumentation

* Remove temp folder of old bootstrap instrumentation requirement.

* Remove javassist dependency

*   Finish the PR.

* Change doc title level.

* Remove the duplicated codes.

* POC: Intercept successfully.

* Refactor codes

* Build the new core

* Setup the new core.

* Push the javassist version to 3.23.2-GA, as it is the last version supports JDK 1.6 compile, according to https://github.com/jboss-javassist/javassist/blob/rel_3_23_2_ga/pom.xml#L149-L160

* Finish the all codes.

* Document updated for bootstrap instrumentation.

* Add a notice to document.

* Remove unexpected file.

* Set javassist version right. Add judge in core interceptors

* Fixe no log bridge implementation

* Fix 3096

* spring_async_plugin

* fix

* fix

* fix

* fix

* format fix

* rename

* fix

* fix version

* Update SWCallable.java

* Update Supported-list.md

* Update Supported-list.md

* AsyncAppender

* improve performance

* fix mdc issue

* fix mdc

* add Async demo

* Support bootstrap class enhance and fix OOM by empty stack of exception.

* Agent document update

* Remove a word.

* Fix wrong cause exception search.

* Fix the condition

* Revert bootstrap class loader enhance.

* Remove import.

* no message

* Add config to control tracing sql parameters

* restore solrj-plugin

* restore solrj-plugin

* Revert SolrJ plugin.

* Remove an unexpected test case.

* Revert "Remove an unexpected test case."

This reverts commit 359990e18b0c0ae1a6e1005ff985bf237ec05619.

* Clear context.

* Fix a leak.

* new branch for solrj-plugin

* rollback and add module solrj-plugin

* preparing to pr

* to resolve reviewers' suggestions

* remove unused code

* remove unused code

* remove unused comments

* To avoid NPE

* fix typo

* Change to JRE6

* fix pom.xml merge incorrectly. and java.net.URL instead of Regex

* Using RuntimeContext instead of ThreadLocal

* To reduce unnecessary tags

* add test cases

* fix validation fail

* add solrj-plugin into component-libraries & Supported-list

* to trace all patch to avoid recheck status of span

* remove unnecessary properites

* remove unnecessary tags

* Add the config to document of setup

* merge

* merge

* Provide plugin for ShardingSphere (#2699)

* Provide plugin for ShardingSphere (#2699)

* Provide plugin for ShardingSphere (#2699)

* adjust package name (#2699)

* fix mvnw (#2699)

* revert files access permission from 644 to 755

* change the access permission from 644 to 755

* change files access permission from 644 to 755

* revert all no changes files

* feat(agent sdk): resteasy plugin

* fix(agent sdk): fix component define

* fix(agent sdk): fix file license

* fix(agent sdk): fix file license

* docs(agent sdk): add supported list

* fix(agent sdk): fix file license

* fix(agent sdk): fix response error tag

* fix(agent sdk): fix

* fix(agent sdk): adapter 3.5+

* fix(agent sdk): remove unreasonable async handling

* spring cloud gateways plugin

* Provide plugin for ShardingSphere (#1933)

* Fix #2546

Update all "incubator-skywalking" to "skywalking" ,"incubator-servicecomb-java-chassis" to "servicecomb-java-chassis" correctly, and ".gitmodules" will update at #2531 (#2548)

* vertx plugin impl

* Submit custom enhancement kernel code for the first time.

* Submit the code again.

* Optimize ClassUtil code.

* Submit custom enhancement plugin code for the first time.

* To fix CI issue.

* To fix CI header Tmp issue

* To fix CI Tmp header issue

* Customize plugin code submission

* Add md file.

* Fix some bug.

* Fix ci issue

* Fix md desc

* Fix unapproved license

* Fix bug

* Fix collection bug.

* Fix java8 pair ref issue

* Fix CI issue.

* Add more detail for expression.

* Fix review issue

* Fix review issue 2

* Fix review code issue 2

* Fix md issue

* Fix bug and op desc md.

* Update customize-enhance-trace.md

* Update customize-enhance-trace.md

* FIx code review issue.

* add instance id configuration item

* add doc about instance uuid

Make supported list more clear.

* Update and rename Spring-bean-plugins.md to Spring-annotation-plugin.md

* Update README.md

* Update README.md

[Performance Improvement]Backend streaming thread model improvement