How to view autoconfigure log output during spring boot server start - spring

Question

How to view autoconfigure log output during spring boot server start
I have created a spring boot application. It uses a shared library (Spring boot jar via maven dependency). Shared library class is loaded via
META-INF/spring.factories
I have mentioned the classes from the library in spring.factories. The job of shared library is to read Vault role id and Vault
secret id value from application.properties and call a REST API and fetch secrets from Vault. After fetching the secret it sets the value again in system property.
for (Map.Entry<String, String> entry : allSecrets.entrySet())
{
System.setProperty(entry.getKey(), entry.getValue());
}
Everything is working as expected. But I am not able to see logs from shared library in my logs.
shared library's package structure is com.myorg.abc. My spring boot package structure is com.myorg.xyz
I tried the following in application properties.
logging.level.root= DEBUG
logging.level.com.myorg.xyz: DEBUG
logging.level.com.myorg.abc: DEBUG
logging.level.org.springframework.boot.autoconfigure.logging=DEBUG
I am able to get logs only from my application but not from shared library. But when I change the shared library Logger.error to System.out, then I am getting the message in my application. How to view shared library's log in my application.

Answer 1

Spring boot initializes logging at least 3 times. The first happens when SpringApplication is loaded. It creates an SLF4J Logger before anything in Spring is accessed. This causes whatever logging implementation you have chosen to initialize. By default, it will use the logging configuration in the Spring jar. With Log4j 2 you can override this by setting log4j.configurationFile to the location of your desired configuration either as a system property or in a log4j.component.properties file.
Everything Spring does will be logged using this configuration until it initializes the logging configuration again, which is controlled by bootstrap.yml. Finally, your application's logging configuration is initialized which is configured either from application.yml or again from bootstrap.yml.

Answer 2

I replaced org.springframework.boot.env.EnvironmentPostProcessor with org.springframework.context.ApplicationListener in Spring.factories and it fixed the issue. I was able to get logs from shared library in invoking application.
Spring.factories
org.springframework.context.ApplicationListener=com.mypackage.MyClassName
MyClassName.java
public class MyClassName implements ApplicationListener<ApplicationPreparedEvent>
{
private static final Logger LOGGER = LoggerFactory.getLogger(MyClassName.class);
#Override
public void onApplicationEvent(ApplicationPreparedEvent applicationPreparedEvent)
{
ConfigurableEnvironment configurableEnvironment = applicationPreparedEvent.getApplicationContext()
.getEnvironment();
String roleId = configurableEnvironment.getProperty(Constants.VAULT_ROLE_ID_LITERAL);
String secretId = configurableEnvironment.getProperty(Constants.VAULT_SECRET_ID_LITERAL);
...
Optional<String> errorMessage = ServiceUtil.validateSystemProperty(roleId, secretId);
if (!errorMessage.isPresent())
{
Map<String, String> secret = ServiceUtil.getSecret(roleId, secretId);
for (Map.Entry<String, String> entry : secret.entrySet())
{
System.setProperty(entry.getKey(), entry.getValue());
}
LOGGER.info("Successfully populated secrets from Vault in system property");
}
else
{
LOGGER.error("Failed to populate secrets from Vault in system property. Error:{}", errorMessage.get());
}
}
}
application.properties
logging.level.com.myorg.abc: DEBUG