[apache#6880] improve(core): Refactor EventBus#dispatchEvent

Refactor EventBus#dispatchEvent.

Author: Abyss-lord

core/src/main/java/org/apache/gravitino/listener/EventBus.java

@@ -22,6 +22,7 @@
 import com.google.common.annotations.VisibleForTesting;
 import java.util.List;
 import org.apache.gravitino.exceptions.ForbiddenException;
+import org.apache.gravitino.listener.api.EventDispatcher;
 import org.apache.gravitino.listener.api.EventListenerPlugin;
 import org.apache.gravitino.listener.api.event.BaseEvent;
 import org.apache.gravitino.listener.api.event.Event;
@@ -38,6 +39,7 @@ public class EventBus {
   // which are meant for synchronous event listening, or AsyncQueueListener, designed for
   // asynchronous event processing.
   private final List<EventListenerPlugin> eventListeners;
+  private final InternalVisitor internalVisitor;
 
   /**
    * Constructs an EventBus with a predefined list of event listeners.
@@ -47,6 +49,7 @@ public class EventBus {
    */
   public EventBus(List<EventListenerPlugin> eventListeners) {
     this.eventListeners = eventListeners;
+    this.internalVisitor = new InternalVisitor();
   }
 
   /**
@@ -56,13 +59,7 @@ public EventBus(List<EventListenerPlugin> eventListeners) {
    * @param baseEvent The event to be dispatched to all registered listeners.
    */
   public void dispatchEvent(BaseEvent baseEvent) {
-    if (baseEvent instanceof PreEvent) {
-      dispatchPreEvent((PreEvent) baseEvent);
-    } else if (baseEvent instanceof Event) {
-      dispatchPostEvent((Event) baseEvent);
-    } else {
-      throw new RuntimeException("Unknown event type:" + baseEvent.getClass().getSimpleName());
-    }
+    baseEvent.accept(internalVisitor);
   }
 
   /**
@@ -77,11 +74,18 @@ List<EventListenerPlugin> getEventListeners() {
     return eventListeners;
   }
 
-  private void dispatchPostEvent(Event postEvent) {
-    eventListeners.forEach(eventListener -> eventListener.onPostEvent(postEvent));
-  }
+  /** Internal visitor is an inner private class that dispatches events to registered listeners. */
+  private class InternalVisitor implements EventDispatcher {
+    /** {@inheritDoc} */
+    @Override
+    public void dispatchPreEvent(PreEvent event) throws ForbiddenException {
+      eventListeners.forEach(eventListener -> eventListener.onPreEvent(event));
+    }
 
-  private void dispatchPreEvent(PreEvent preEvent) throws ForbiddenException {
-    eventListeners.forEach(eventListener -> eventListener.onPreEvent(preEvent));
+    /** {@inheritDoc} */
+    @Override
+    public void dispatchPostEvent(Event event) {
+      eventListeners.forEach(eventListener -> eventListener.onPostEvent(event));
+    }
   }
 }

core/src/main/java/org/apache/gravitino/listener/api/EventDispatcher.java

@@ -0,0 +1,43 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.gravitino.listener.api;
+
+import org.apache.gravitino.exceptions.ForbiddenException;
+import org.apache.gravitino.listener.api.event.Event;
+import org.apache.gravitino.listener.api.event.PreEvent;
+
+/** Defines the contract for dispatching events to registered listeners. */
+public interface EventDispatcher {
+
+  /**
+   * Dispatches a {@link PreEvent} to the appropriate listener.
+   *
+   * @param event the pre-event to be dispatched.
+   * @throws ForbiddenException if the dispatch is not permitted by the plugin.
+   */
+  void dispatchPreEvent(PreEvent event) throws ForbiddenException;
+
+  /**
+   * Dispatches a {@link Event} (post-event) to the appropriate listener.
+   *
+   * @param event the post-event to be dispatched.
+   */
+  void dispatchPostEvent(Event event);
+}

core/src/main/java/org/apache/gravitino/listener/api/event/BaseEvent.java

@@ -24,6 +24,7 @@
 import javax.annotation.Nullable;
 import org.apache.gravitino.NameIdentifier;
 import org.apache.gravitino.annotation.DeveloperApi;
+import org.apache.gravitino.listener.api.EventDispatcher;
 
 /**
  * The abstract base class for all events. It encapsulates common information such as the user who
@@ -50,6 +51,13 @@ protected BaseEvent(String user, NameIdentifier identifier) {
     this.eventTime = System.currentTimeMillis();
   }
 
+  /**
+   * Accept a visitor to process the event itself.
+   *
+   * @param visitor the implementation of the visitor interface.
+   */
+  public abstract void accept(EventDispatcher visitor);
+
   /**
    * Retrieves the user associated with this event.
    *

core/src/main/java/org/apache/gravitino/listener/api/event/Event.java

@@ -21,11 +21,18 @@
 
 import org.apache.gravitino.NameIdentifier;
 import org.apache.gravitino.annotation.DeveloperApi;
+import org.apache.gravitino.listener.api.EventDispatcher;
 
 /** Represents a post event. */
 @DeveloperApi
 public abstract class Event extends BaseEvent {
   protected Event(String user, NameIdentifier identifier) {
     super(user, identifier);
   }
+
+  /** {@inheritDoc} */
+  @Override
+  public void accept(EventDispatcher visitor) {
+    visitor.dispatchPostEvent(this);
+  }
 }

core/src/main/java/org/apache/gravitino/listener/api/event/PreEvent.java

@@ -21,6 +21,7 @@
 
 import org.apache.gravitino.NameIdentifier;
 import org.apache.gravitino.annotation.DeveloperApi;
+import org.apache.gravitino.listener.api.EventDispatcher;
 
 /** Represents a pre event. */
 @DeveloperApi
@@ -29,6 +30,13 @@ protected PreEvent(String user, NameIdentifier identifier) {
     super(user, identifier);
   }
 
+  /** {@inheritDoc} */
+  @Override
+  public void accept(EventDispatcher visitor) {
+    visitor.dispatchPreEvent(this);
+  }
+
+  /** {@inheritDoc} */
   @Override
   public OperationStatus operationStatus() {
     return OperationStatus.UNPROCESSED;