> Markdown version of [Service Init Listener](https://vaadin.com/docs/latest/flow/advanced/service-init-listener). Section index: [llms.txt](https://vaadin.com/docs/latest/flow/llms.txt)

# Service Init Listener

The `ServiceInitEvent` is fired when your Vaadin application starts. It’s a good place to configure the `RequestHandler`, `IndexHtmlRequestListener` and [`DependencyFilter`](https://vaadin.com/docs/latest/flow/advanced/dependency-filter.md) objects. You can also use it to [dynamically register routes](https://vaadin.com/docs/latest/flow/routing/dynamic.md#application.startup) during application startup, and to [register session and UI listeners](https://vaadin.com/docs/latest/flow/advanced/session-and-ui-init-listener.md).

In Spring and CDI applications, the `ServiceInitEvent` is fired as an application event. It’s enough to annotate your bean method accepting `ServiceInitEvent` as a parameter with the [`@EventListener`](https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/context/event/EventListener.html) (Spring) or [`@Observes`](https://jakarta.ee/specifications/cdi/4.0/apidocs/jakarta.cdi/jakarta/enterprise/event/observes) (CDI) annotation. The following shows an example of this:

```java
@Component
public class MyBean {

    @EventListener
    public void logSessionInits(ServiceInitEvent event) {
        event.getSource().addSessionInitListener(
                sessionInitEvent -> LoggerFactory.getLogger(getClass())
                        .info("A new Session has been initialized!"));
    }

}
```

Alternatively, you can implement the `VaadinServiceInitListener` interface and register it, like shown in the following example:

```java
public class ApplicationServiceInitListener
        implements VaadinServiceInitListener {

    @Override
    public void serviceInit(ServiceInitEvent event) {
        event.addIndexHtmlRequestListener(response -> {
            // IndexHtmlRequestListener to change the bootstrap page
        });

        event.addDependencyFilter((dependencies, filterContext) -> {
            // DependencyFilter to add/remove/change dependencies sent to
            // the client
            return dependencies;
        });

        event.addRequestHandler((session, request, response) -> {
            // RequestHandler to change how responses are handled
            return false;
        });
    }

}
```

In a Spring or CDI project, all beans implementing the `VaadinServiceInitListener` interface are registered automatically. Remember to add the `@Component` annotation to the class, to make it a managed bean.

In plain Java projects, the listener should be registered as a provider via the Java Service Provider Interface (SPI) loading facility. To do this, you should create the `META-INF/services` resource directory and a provider configuration file with the name `com.vaadin.flow.server.VaadinServiceInitListener`. This is a text file and should contain the fully qualified name of the `ApplicationServiceInitListener` class on its own line. It allows the application to discover the `ApplicationServiceInitListener` class, instantiate it and register it as a service init listener for the application.

[Image: A screenshot showing the file and folder structure of a Vaadin project]

Location of the Configuration File

The content of the configuration file should look like this, as an example (replace `com.mycompany` with the package name of your implementation):

```
com.mycompany.ApplicationServiceInitListener
```

The following pages offer more details about Java SPI loading:

- <https://docs.oracle.com/javase/tutorial/ext/basics/spi.html#register-service-providers>

- <https://docs.oracle.com/javase/7/docs/api/java/util/ServiceLoader.html>

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