[BAEL-4612] get spring boot port at runtime

spring-boot-modules/spring-boot-environment/src/main/java/com/baeldung/serverport/GetServerPortApplication.java

@@ -0,0 +1,12 @@
+package com.baeldung.serverport;
+
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class GetServerPortApplication {
+    public static void main(String[] args) {
+        SpringApplication.run(GetServerPortApplication.class, args);
+    }
+}

spring-boot-modules/spring-boot-environment/src/main/java/com/baeldung/serverport/ServerPortService.java

@@ -0,0 +1,20 @@
+package com.baeldung.serverport;
+
+import org.springframework.boot.web.servlet.context.ServletWebServerInitializedEvent;
+import org.springframework.context.event.EventListener;
+import org.springframework.stereotype.Service;
+
+@Service
+public class ServerPortService {
+    private int port;
+
+    public int getPort() {
+        return port;
+    }
+
+    @EventListener
+    public void onApplicationEvent(final ServletWebServerInitializedEvent event) {
+        port = event.getWebServer().getPort();
+    }
+
+}