Override spring logback path after app startup in runtime - spring-boot

Question

I have a spring boot application that uses spring logback for logging. My application is being deployed in an external tomcat. By default the path taken up by the log file resides in tomcat's directory rather than webapp roots sub directory.
Eg: instead of creating the logs inside tomcat -> logs -> app.log
I would like it to be under tomcat -> webapps -> spring-app -> logs -> app.log
Since the path is only known at runtime, I have declared a logback-configuration as app-logback-spring.xml used springProperty to populate the path.
public class LoggingInitializer implements ApplicationContextInitializer{
#Override
public void initialize(ConfigurableApplicationContext appContext) {
try {
URI uri = appContext.getResource("/").getURI();
File file = new File(uri);
Map<String, Object> properties = new HashMap<>();
properties.put("app-root.path", file.getAbsolutePath());
properties.put("app.log.path", file.getAbsolutePath()+"/logs");
System.out.println("props "+properties);
MapPropertySource mapPropSrc = new MapPropertySource("custom", properties);
appContext.getEnvironment().getPropertySources().addFirst(mapPropSrc);
LoggerContext loggerContext = (LoggerContext) LoggerFactory.getILoggerFactory();
JoranConfigurator configurator = new JoranConfigurator();
File configFile = new File(file.getAbsolutePath()+File.separator+"WEB-INF"+File.separator
+"classes"+File.separator+"app-logback-spring.xml");
InputStream configStream = Files.newInputStream(configFile.toPath());
configurator.setContext(loggerContext);
configurator.doConfigure(configStream); // loads logback file
configStream.close();
} catch (IOException e) {
throw new CustomException("Could not initialize application", e);
} catch (JoranException e) {
throw new CustomException("Error configuring logger", e);
}
}
}
<configuration>
<springProperty scope="context" name="logpath" source="app.log.path"/>
<appender name="RollingFile"
class="ch.qos.logback.core.rolling.RollingFileAppender">
<file>${logpath}/app.log</file>
---
---
</configuration>
However, during the initialization I suppose the logpath is not recognized. I infer it based on a folder that is created under tomcat with name logpath_IS_UNDEFINED and the app.log goes under it.
The app-root.path that I set is available for services with correct value. I know I can write to app-logback-spring.xml before reading it, but that looks like a convoluted way.
Is it because when the logger is loading, the spring property is not available is it?