Modify existing log4j2 FileAppender configuration during runtime - log4j2

Question

I am migrating application (huge web application) from log4j1.x to log4j 2.11.0.
I need help/clarification to migrate following scenarios -
--------scenario1
log4j1.x:
<appender name="import_log_file" class="xxxx">
During runtime i want to change the file so i would just do appender.setFile(...new file...). And done.
log4j2:
how do I migrate above code?
Few ideas but not a straight answer:
Creating brand new appender via LoggerContext, Configuration might be a way but i want to update an existing appender's configuration and reload the log4j2 xml. How do I do that?
Another way could be redefining something like this
<appender name="import_log_file" class="xxxx">
And then setup "dynamic_name" property in threadcontext. But I am loosing original default file import.log
Any help is appreciated. Let me know if you have ideas.

Answer 1

During runtime i want to change the file
You can use the RoutingAppender together with a lookup to do this. See the log4j2 FAQ page for details.
Here is a very simple example of how to change the log file name at runtime:
package pkg;
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.ThreadContext;
public class Log4j2DiffFilePerCtxVarMain {
private static final Logger LOG = LogManager.getLogger();
public static void main(String[] args){
ThreadContext.put("myFileNameVar", "file1");
LOG.info("This should appear in file1.log");
ThreadContext.put("myFileNameVar", "file2");
LOG.info("This should appear in file2.log");
}
}
The configuration looks like this:
<?xml version="1.0" encoding="UTF-8"?>
<Configuration status="WARN">
<Appenders>
<Routing name="myAppender">
<Routes pattern="$${ctx:myFileNameVar}">
<Route>
<File
fileName="logs/${ctx:myFileNameVar}.log"
name="myAppender-${ctx:myFileNameVar}">
<PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/>
</File>
</Route>
</Routes>
</Routing>
</Appenders>
<Loggers>
<Root level="trace">
<AppenderRef ref="myAppender" />
</Root>
</Loggers>
</Configuration>
The result of running the above code will be two files - file1.log an file2.log each with a single entry. The file1.log will contain the first log message and file2.log will contain the second message.
Hope this helps!