* Support timeout configuration in agent and backend.

* Fix CI

* no message

* Add feature to control the maximum history agent log files.

* Add Light4J 1.6.x plug-in

* Add unit test for Light4J plug-in

* Add missing id to server-starter

* Remove mentions of version 1.6.x

Some local testing showed that the plugin successfully generated traces for a light4j project built with light-codegen v2.x. Therefore, there is no need for a separate plugin for v2.x and no distinction needs to be made with light4j v1.6.x.

* Update supported light4j versions

* Use ContextSnapshot to maintain trace

In a typical Light4j project, the ExceptionHandler#handleRequest is the asynchronous execution point. The flow is ExceptionHandler#handleRequest -> HttpServerExchange#dispatch -> ... -> ExceptionHandler#handleRequest. This means that handleRequest is being intercepted twice and each time a LocalSpan is created. Without handling thread propagation, the trace segment gets split up.

By saving a ContextSnapshot into the enhanced object (ExceptionHandler), we can determine if it is necessary to continue the segment.

* Update logic for span creation in trace

By default, the Light4J plugin now overrides the Undertow plugin's entry span with its own. This new entry span is created just before execution of the ExceptionHandler#handleRequest in the I/O thread. The entry span is generated here because it is considered the starting point of the Light4J handler chain.

There is now also the option to enable detailed span creation when tracing requests through Light4J. These local spans mark which middleware and business handlers are involved with handling the HTTP request to a Light4J service.

* Update skywalking version

* Update light4j version

* Fix LightInstrumentation javadoc

* Remove import violating checkstyle

This import was added from the link reference in the javadoc. The javadoc has now been changed to just reference the method name.

* Move light4j agent config property

* Sync UI

* agent support custom properties.

* 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.

* 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

* 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

* spring cloud gateways plugin

* 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

* Zookeeper plugin

* Make sure all document images ref from our Apache website.

* Change the statement.

* Support lettuce plugin

* lettuce plugin bugfix

* lettuce plugin fix license issue

* lettuce plugin fix cluster and config issue

* plugin lettuce compatible with low 5.0.x version

* lettuce plugin support version accurately describes on Supported-list.md

* plugin lettuce compatible with low 5.0.2 version

* lettuce plugin fix wrong batch method intercept point

* move lettuce to optional plugins

* fix ci issue

* fix ci issue

* Modify the description file

* Pom code optimization

* Optimization operation name

* Optimization operation name2

correct spelling error.

* Support Gson plugin

* Update README.md

* Update README.md

* feat:Active System.env Config In Both Collector And agent.config.
1、moving related codes into apm-util module.
2、update Setting-override.md about how to use.

* resolve docs.

* typo

* finish test case.

* Update README.md

* Update new protocol

* Support new protocol at agent side.

* Fix test case.

* Make backend supports new trace protocol

* Fix tests.

* Make all new services available in gRPC.

* Fix bugs.

* Finish new document for v2 trace protocol.

* Fix wrong version requirement of zk

* Fix trace query bug.

* Find a client side dictionary bug.

* Fix register bugs.

* Fix break doc links.

Fix typo

* Replace v5 changes by a link to 5.x branch. New v6 changelog.

* Finish query doc and fix a missing field in alarm doc.

* Add link to official oal in alarm doc.

* Fix words.

* Fix some doc

* Update README.md

* Update README.md

* Update README.md

* Update README.md