SpringBoot start time will call the method SpringApplicationRunListener # contextLoaded, event class that contains the following:
EventPublishingRunListener and custom SpringApplicationRunListener
EventPublishingRunListener release
ApplicationPreparedEvent event
ConfigFileApplicationListener monitor
ApplicationEvent event processing
ApplicationPreparedEvent event
Extension point
Custom SpringApplicationRunListener, rewrite method contextLoaded
custom ApplicationListener, listening ApplicationPreparedEvent event