Code Recipes Blog

In this post under Spring Core, I will show with example how to create custom application events.

For our example, I created a custom event that the application will generate as shown below

CustomEvent

package package32;

import org.springframework.context.ApplicationEvent;

public class CustomEvent extends ApplicationEvent {
    public CustomEvent(Object source) {
        super(source);
    }
}

In the above code, I created a class named “CustomEvent” and it extends Spring’s “ApplicationEvent” class. Extending “ApplicationEvent” class is required to create a custom event class.

Now I will create a listener, that will listen to the above event and execute the code when the event is generated.

Listener

package package32;

import org.springframework.context.event.EventListener;
import org.springframework.stereotype.Component;

@Component
public class CustomEventListener {
    @EventListener
    public void customEventListener(CustomEvent customEvent) {
        System.out.println("Custom Event Generated");
    }
}

In the above code, we create a class “CustomEventListener” and added a method “customEventListener” method.

The method “customEventListener” takes “CustomEvent” instance as a parameter. The method is also annotated with “@EventListener” annotation. Annotating the method with “@EventListener” is important.

Below is the main class that shows how to publish the event.

Main class

1  package package32;
2  
3  import org.springframework.context.ApplicationContext;
4  import org.springframework.context.ApplicationEventPublisher;
5  import org.springframework.context.annotation.AnnotationConfigApplicationContext;
6  import org.springframework.context.annotation.ComponentScan;
7  
8  @ComponentScan(basePackages = "package32")
9  public class Example32 {
10 
11     public static void main(String[] args) {
12         ApplicationContext applicationContext = new AnnotationConfigApplicationContext(Example32.class);
13         Example32 example32 = applicationContext.getBean(Example32.class);
14         example32.publishEvent(applicationContext);
15     }
16 
17     public void publishEvent(ApplicationEventPublisher applicationEventPublisher) {
18         CustomEvent customEvent = new CustomEvent(this);
19         applicationEventPublisher.publishEvent(customEvent);
20     }
21 }

In the above class main method, I create an instance of “AnnotationConfigApplicationContext” named “applicationContext”

This instance “applicationContext” already implments the interface “ApplicationEventPublisher”.

At line 13, I get an instance of “Example32” using “getBean” method.

At line 14, I call “publishEvent” method passing the instance “applicationContext” as an argument.

In the method “publishEvent”, at line 18, I create an instance of “CustomEvent” class passing “Example32” instance as an constructor argument making it the source of the event.

At line 19, I call “publishEvent” method of “applicationEventPublisher” and pass the event instance as method argument.

In this way I publish the event and once published, the “CustomEventListener” instance will execute the method “customEventListener”.

In this way we can publish and listen to custom event.