Listening for Serve Events#

Serve event listeners are intended for use when you wish to take an action at a specific point in the request processing flow, without affecting processing in any way. For instance a serve event listener would be the most suitable extension point to use for exporting telemetry data to a monitoring/observability tool.

The ServeEventListener interface (which deprecates PostServeAction) supports two different modes of operation - you can either override specific methods if the listener should only fire at a specific point in the request processing flow, or you can override a generic method then configure which lifecycle points it's fired at when binding the listener to specific stubs. Or it can simply be made to fire at all lifecycle points.

Listening for specific lifecycle events#

The ServeEventListener interface has a set of callback methods that can be implemented for specific points in the request lifecycle. These have no-op defaults, so you can override just the ones that are relevant:

public class MyServeEventListener implements ServeEventListener {

    @Override
    public void beforeMatch(ServeEvent serveEvent, Parameters parameters) {
        // Do something before request matching
    }

    @Override
    public void afterMatch(ServeEvent serveEvent, Parameters parameters) {
        // Do something after request matching
    }

    @Override
    public void beforeResponseSent(ServeEvent serveEvent, Parameters parameters) {
        // Do something before the response is sent to the client
    }

    @Override
    public void afterComplete(ServeEvent serveEvent, Parameters parameters) {
        // Do something after the response has been sent to the client
    }

    @Override
    public String getName() {
        return "my-listener";
    }
}

Listening for all lifecycle events#

The alternative approach you can take is to listen for all events along with a request phase value indicating when the event fired:

public class MyServeEventListener implements ServeEventListener {

    @Override
    public void onEvent(
        RequestPhase requestPhase,
        ServeEvent serveEvent,
        Parameters parameters) {

        log.debug("Received serve event in phase " + requestPhase);
    }

    @Override
    public String getName() {
        return "my-listener";
    }
}