How to use system property variable in log4j2.xml in spring boot using lombok log?

Question

I am having a CommandLineRunner Spring Boot applicatio nwith Sytem property log_prefix.

I am currently using a log24j.xml for setting the log configurations. It is taking the filename etc from the <properites> tag in the log24j.xml. Is there a way to change the log fileName to log_prefix_LogFileName ?

My Application.class

@SpringBootApplication
public class Application implements CommandLineRunner {
    static Logger log = Logger.getLogger(Application.class.getName());
    public static void main(String[] args) {
        System.setProperty("log_prefix",args[0]);// Tried hardcoding a string value
        SpringApplication springApplication = new SpringApplication(Application.class);
        springApplication.run(args);
    }

I tried setting runID in Application.class and using ${log_prefix} in log42j.xml but not working.

Pom.xml log4j2 dependency.

 <log4j2.version>2.15.0</log4j2.version>

I am using @Slf4j lombok annotaion over the class

import lombok.extern.slf4j.Slf4j;
@Slf4j

Duplicated https://stackoverflow.com/questions/19132433/one-logfile-per-run-with-log4j — Halil İbrahim Oymacı, Oct 23 '22 at 11:39
@HalilİbrahimOymacı updated question for more clarity. I have changed the runID variable to log_prefix for more clarity on the error. — Thy, Oct 23 '22 at 13:34
`Logger.getLogger` is executed before your application starts and it configures Log4j2. — Piotr P. Karwasz, Oct 24 '22 at 19:13
@PiotrP.Karwasz True, I tried reconfiguring log as in https://www.tabnine.com/code/java/methods/org.apache.logging.log4j.core.LoggerContext/reconfigure but didn't work. — Thy, Oct 25 '22 at 06:38
In the config file you must use `${sys:log_prefix}` to access system properties. — Piotr P. Karwasz, Oct 25 '22 at 07:39
Removing business use case in the question to make it generic. — Thy, Oct 31 '22 at 10:14

score 1 · Accepted Answer · answered Oct 31 '22 at 10:13

As Piotr P Karwaz pointed out my log config file had ${log_prefix} , to get system properties in spring boot log configuration log4j2.xml file we need to prefix sys: the property name in curly braces. ${sys:log_prefix} fixed the issue.

note this is specific to Spring boot, for normal java application you can refer this answer

How to use system property variable in log4j2.xml in spring boot using lombok log?

1 Answers1