Add ApplicationListener example

spring-all/pom.xml

@@ -130,6 +130,13 @@
             <scope>test</scope>
         </dependency>
 
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>3.5.1</version>
+            <scope>test</scope>
+        </dependency>
+
         <dependency>
             <groupId>org.hamcrest</groupId>
             <artifactId>hamcrest-core</artifactId>

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++;
+    }
+}

spring-all/src/test/java/org/baeldung/startup/SpringStartupTest.java

@@ -1,5 +1,6 @@
 package org.baeldung.startup;
 
+import org.assertj.core.api.Assertions;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.springframework.beans.factory.BeanCreationException;
@@ -35,4 +36,9 @@ public class SpringStartupTest {
     public void whenInitializingBean_shouldLogEnv() throws Exception {
         ctx.getBean(InitializingBeanExampleBean.class);
     }
+
+    @Test
+    public void whenApplicationListener_shouldRunOnce() throws Exception {
+        Assertions.assertThat(StartupApplicationListenerExample.counter).isEqualTo(1);
+    }
 }