content: /*
   * 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.kafka.common;
  
  /**
   * A callback interface that users can implement when they wish to get notified about changes in the Cluster metadata.
   * <p>
   * Users who need access to cluster metadata in interceptors, metric reporters, serializers and deserializers
   * can implement this interface. The order of method calls for each of these types is described below.
   * <p>
   * <h4>Clients</h4>
   * There will be one invocation of {@link ClusterResourceListener#onUpdate(ClusterResource)} after each metadata response.
   * <p>
   * {@link org.apache.kafka.clients.producer.ProducerInterceptor} : The {@link ClusterResourceListener#onUpdate(ClusterResource)} method will be invoked after {@link org.apache.kafka.clients.producer.ProducerInterceptor#onSend(org.apache.kafka.clients.producer.ProducerRecord)}
   * but before {@link org.apache.kafka.clients.producer.ProducerInterceptor#onAcknowledgement(org.apache.kafka.clients.producer.RecordMetadata, Exception)} .
   * <p>
   * {@link org.apache.kafka.clients.consumer.ConsumerInterceptor} : The {@link ClusterResourceListener#onUpdate(ClusterResource)} method will be invoked before {@link org.apache.kafka.clients.consumer.ConsumerInterceptor#onConsume(org.apache.kafka.clients.consumer.ConsumerRecords)}
   * <p>
   * {@link org.apache.kafka.common.serialization.Serializer} : The {@link ClusterResourceListener#onUpdate(ClusterResource)} method will be invoked before {@link org.apache.kafka.common.serialization.Serializer#serialize(String, Object)}
   * <p>
   * {@link org.apache.kafka.common.serialization.Deserializer} : The {@link ClusterResourceListener#onUpdate(ClusterResource)} method will be invoked before {@link org.apache.kafka.common.serialization.Deserializer#deserialize(String, byte[])}
   * <p>
   * {@link org.apache.kafka.common.metrics.MetricsReporter} : The {@link ClusterResourceListener#onUpdate(ClusterResource)} method will be invoked after first {@link org.apache.kafka.clients.producer.KafkaProducer#send(org.apache.kafka.clients.producer.ProducerRecord)} invocation for Producer metrics reporter
   * and after first {@link org.apache.kafka.clients.consumer.KafkaConsumer#poll(java.time.Duration)} invocation for Consumer metrics
   * reporters. The reporter may receive metric events from the network layer before this method is invoked.
   * <h4>Broker</h4>
   * There is a single invocation {@link ClusterResourceListener#onUpdate(ClusterResource)} on broker start-up and the cluster metadata will never change.
   * <p>
   * KafkaMetricsReporter : The {@link ClusterResourceListener#onUpdate(ClusterResource)} method will be invoked during the bootup of the Kafka broker. The reporter may receive metric events from the network layer before this method is invoked.
   * <p>
   * {@link org.apache.kafka.common.metrics.MetricsReporter} : The {@link ClusterResourceListener#onUpdate(ClusterResource)} method will be invoked during the bootup of the Kafka broker. The reporter may receive metric events from the network layer before this method is invoked.
   */
  public interface ClusterResourceListener {
      /**
       * A callback method that a user can implement to get updates for {@link ClusterResource}.
       * @param clusterResource cluster metadata
       */
      void onUpdate(ClusterResource clusterResource);
  }
  