How to set log4j path on startup in web app?

I have a log4j2.xml configuration file that should get the logging path dynamically set during startup of the web application by java code.

log4j2.xml:

<Properties>
    <property name="path">{web:attr.logpath}</property>
</Properties>

Therefore I have the following configuration file:

@Configuration
@Order(Ordered.HIGHEST_PRECEDENCE)
public class LogConfig extends SpringBootServletInitializer {
    @Override
    public void onStartup(ServletContext servletContext) throws ServletException {
        servletContext.addListener(Log4jConfigListener.class);
        servletContext.setAttribute("logpath", "d:/testpath");
        super.onStartup(servletContext);
    }
}

Problem: When onStartup() is entered, the log4j initialization is already over and I get the message that log4j path is invalid.

How can I delay the log4j initialization after the attributes have been set?