Web Server Graceful Shutdown

[rscoz]

The purpose of this PR is to enable a graceful shutdown for the application and to introduce additional log levels.

You can find more information on this topic at the following link: Spring Boot Web Server Shutdown

Also modify the script to use exec for running the Java application. This approach is particularly useful when utilising Docker/Kubernetes, as it enables signal reception at PID1.

2023-05-17 23:05:00.507 DEBUG 1 --- [ionShutdownHook] o.s.b.a.ApplicationAvailabilityBean      : Application availability state ReadinessState changed from ACCEPTING_TRAFFIC to REFUSING_TRAFFIC
2023-05-17 23:05:00.513 DEBUG 1 --- [ionShutdownHook] ConfigServletWebServerApplicationContext : Closing org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@3567135c, started on Wed May 17 23:03:56 UTC 2023
2023-05-17 23:05:00.523  INFO 1 --- [ionShutdownHook] o.s.b.web.embedded.jetty.JettyWebServer  : Commencing graceful shutdown. Waiting for active requests to complete
2023-05-17 23:05:00.527  INFO 1 --- [ jetty-shutdown] o.s.b.web.embedded.jetty.JettyWebServer  : Graceful shutdown complete
2023-05-17 23:05:00.539  INFO 1 --- [ionShutdownHook] o.e.jetty.server.AbstractConnector       : Stopped ServerConnector@38364841{HTTP/1.1, (http/1.1)}{0.0.0.0:8080}
2023-05-17 23:05:00.540  INFO 1 --- [ionShutdownHook] org.eclipse.jetty.server.session         : node0 Stopped scavenging
2023-05-17 23:05:00.541  INFO 1 --- [ionShutdownHook] o.e.j.s.h.ContextHandler.application     : Destroying Spring FrameworkServlet 'dispatcherServlet'
2023-05-17 23:05:00.543  INFO 1 --- [ionShutdownHook] o.e.jetty.server.handler.ContextHandler  : Stopped o.s.b.w.e.j.JettyEmbeddedWebAppContext@37e547da{application,/,[file:///tmp/jetty-docbase.8080.7305229179307511171/],STOPPED}