Add ApplicationListener example

spring-all/src/main/java/org/baeldung/startup/StartupApplicationListenerExample.java

@@ -0,0 +1,16 @@
+package org.baeldung.startup;
+
+import org.springframework.context.ApplicationListener;
+import org.springframework.context.event.ContextRefreshedEvent;
+import org.springframework.stereotype.Component;
+
+@Component
+public class StartupApplicationListenerExample implements ApplicationListener<ContextRefreshedEvent> {
+
+    public static int counter;
+
+    @Override
+    public void onApplicationEvent(ContextRefreshedEvent event) {
+        counter++;
+    }
+}