```
https://yourapi.com/invoices/?callback_url=https://www.external.org/events
```

使用如下 JSON 请求体：

```JSON
{
    "id": "2expen51ve",
    "customer": "Mr. Richie Rich",
    "total": "9999"
}
```

然后，您的 API 就会处理发票，并在某个点之后，发送回调请求至 `callback_url`（外部 API）：

```
https://www.external.org/events/invoices/2expen51ve
```

JSON 请求体包含如下内容：

```JSON
{

      throw AssertionError("full event sequence: $fullEventSequence", e)
    }
  }

  /**
   * Remove and return the next event from the recorded sequence.
   *
   * @param eventClass a class to assert that the returned event is an instance of, or null to
   *     take any event class.
   * @param elapsedMs the time in milliseconds elapsed since the immediately-preceding event, or
   *     -1L to take any duration.
   */

	notificationEventsErrorsTotalMD     = NewCounterMD(notificationEventsErrorsTotal, "Events that were failed to be sent to the targets")
	notificationEventsSentTotalMD       = NewCounterMD(notificationEventsSentTotal, "Total number of events sent to the targets")
	notificationEventsSkippedTotalMD    = NewCounterMD(notificationEventsSkippedTotal, "Events that were skipped to be sent to the targets due to the in-memory queue being full")
)

import java.util.Collection;

import org.apache.maven.api.Event;
import org.apache.maven.api.EventType;
import org.apache.maven.api.Listener;
import org.apache.maven.eventspy.EventSpy;
import org.apache.maven.execution.ExecutionEvent;

/**
 * Bridges between Maven3 events and Maven4 events.
 */
@Named
@Singleton
public class EventSpyImpl implements EventSpy {
    @Override

import org.apache.maven.wagon.TransferFailedException;
import org.apache.maven.wagon.UnsupportedProtocolException;
import org.apache.maven.wagon.Wagon;
import org.apache.maven.wagon.events.TransferEvent;
import org.apache.maven.wagon.events.TransferListener;
import org.apache.maven.wagon.observers.AbstractTransferListener;
import org.apache.maven.wagon.observers.Debug;
import org.codehaus.plexus.testing.PlexusTest;

    return NANOSECONDS.toMillis(stopwatch.instant - startTime);
  }

  private void assertEvents(String... events) {
    assertEquals(Arrays.toString(events), stopwatch.readEventsAndClear());
  }

  /**
   * The stopwatch gathers events and presents them as strings. R0.6 means a delay of 0.6 seconds
   * caused by the (R)ateLimiter U1.0 means the (U)ser caused the stopwatch to sleep for a second.

    return NANOSECONDS.toMillis(stopwatch.instant - startTime);
  }

  private void assertEvents(String... events) {
    assertEquals(Arrays.toString(events), stopwatch.readEventsAndClear());
  }

  /**
   * The stopwatch gathers events and presents them as strings. R0.6 means a delay of 0.6 seconds
   * caused by the (R)ateLimiter U1.0 means the (U)ser caused the stopwatch to sleep for a second.

/// tip | Tipp

Beachten Sie, dass wir async/await mit dem neuen `AsyncClient` verwenden – der Request ist asynchron.

///

/// warning | Achtung

https://yourapi.com/invoices/?callback_url=https://www.external.org/events
```

с телом JSON:

```JSON
{
    "id": "2expen51ve",
    "customer": "Mr. Richie Rich",
    "total": "9999"
}
```

то *ваш API* обработает счёт и, в какой-то момент позже, отправит запрос обратного вызова на `callback_url` (*внешний API*):

```
https://www.external.org/events/invoices/2expen51ve
```

import org.apache.maven.api.annotations.Nonnull;

/**
 * Event sent by maven during various phases of the build process.
 * Such events can be listened to using {@link Listener}s objects
 * registered in the {@link Session}.
 *
 * @since 4.0.0
 */
@Experimental
public interface Event {

    /**
     * Gets the type of the event.
     *
     * @return the type of the event, never {@code null}
     */
    @Nonnull