Dyanmically populating a variable in a log file - dynamic

Question

I have a web service (Jenkins) that handles user requests, and I want to be able to dynamically append the request session id to each log line without having to actually add that variable to each and every log action.
I'm using log4j2 with slf4j implementation, I initialize the logger using an external configuration file with org.apache.logging.log4j.core.config.Configurator, I create an instance of the logger per every session using
final Logger logger = LoggerFactory.getLogger(MyClass.class);
I have for example:
logger.debug("received new request");
...
logger.debug("added something");
And I want the user session id to be added to each line without having to add it myself like:
logger.debug("{} received new request",session.getId());
...
logger.debug("{} added something",session.getId());
My log4j2.xml file is:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE xml>
<Configuration status="INFO">
<Properties>
<Property name="logPath">...</Property>
<Property name="rollingFileName">...</Property>
</Properties>
<Appenders>
<Console name="console" target="SYSTEM_OUT">
<PatternLayout pattern="[%highlight{%-5level}] %d{DEFAULT} %c{1}.%M() - %msg%n%throwable{short.lineNumber}" />
</Console>
<RollingFile name="rollingFile" fileName="${logPath}/${rollingFileName}.log" filePattern="${logPath}/${rollingFileName}_%d{yyyy-MM-dd}.log">
<PatternLayout pattern="[%highlight{%-5level}] %d{DEFAULT} %c{1}.%M() - %msg%n%throwable{short.lineNumber}" />
<Policies>
<!-- Causes a rollover if the log file is older than the current JVM's start time -->
<OnStartupTriggeringPolicy />
<!-- Causes a rollover once the date/time pattern no longer applies to the active file -->
<TimeBasedTriggeringPolicy interval="1" modulate="true" />
</Policies>
</RollingFile>
</Appenders>
<Loggers>
<Logger name="com.project" level="debug" additivity="false">
<AppenderRef ref="console"/>
<AppenderRef ref="rollingFile"/>
</Logger>
</Loggers>
</Configuration>
Actual results from current log file:
[[36mDEBUG[m] 2019-02-05 16:42:09,794 SpellCheck.getResult() - start
[[36mDEBUG[m] 2019-02-05 16:42:10,420 SpellCheck.getResult() - Spelling correction returned no results.
[[36mDEBUG[m] 2019-02-05 16:42:10,420 SpellCheck.getResult() - end
What I want to achieve:
[[36mDEBUG[m] 2019-02-05 16:42:09,794 SpellCheck.getResult() - 1234 - start
[[36mDEBUG[m] 2019-02-05 16:42:10,420 SpellCheck.getResult() - 1234 - Spelling correction returned no results.
[[36mDEBUG[m] 2019-02-05 16:42:10,420 SpellCheck.getResult() - 1234 - end
Where 1234 is for example the session id.
Thanks.

Answer 1

I figured it out, was a lot easier than I thought.
Basically added %X{userSessionId} to the
<PatternLayout pattern= ... />
row in log4j2.xml.
And in the code added
HttpSession session = request.getSession();
org.apache.logging.log4j.ThreadContext.put("userSessionId", session.getId());