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.config.provider;
  
  import org.apache.kafka.common.Configurable;
  import org.apache.kafka.common.config.ConfigChangeCallback;
  import org.apache.kafka.common.config.ConfigData;
  
  import java.io.Closeable;
  import java.util.Set;
  
  /**
   * A provider of configuration data, which may optionally support subscriptions to configuration changes.
   * <p>Implementations are required to safely support concurrent calls to any of the methods in this interface.
   * <p>Kafka Connect discovers implementations of this interface using the Java {@link java.util.ServiceLoader} mechanism.
   * To support this, implementations of this interface should also contain a service provider configuration file in
   * {@code META-INF/services/org.apache.kafka.common.config.provider.ConfigProvider}.
   */
  public interface ConfigProvider extends Configurable, Closeable {
  
      /**
       * Retrieves the data at the given path.
       *
       * @param path the path where the data resides
       * @return the configuration data
       */
      ConfigData get(String path);
  
      /**
       * Retrieves the data with the given keys at the given path.
       *
       * @param path the path where the data resides
       * @param keys the keys whose values will be retrieved
       * @return the configuration data
       */
      ConfigData get(String path, Set<String> keys);
  
      /**
       * Subscribes to changes for the given keys at the given path (optional operation).
       *
       * @param path the path where the data resides
       * @param keys the keys whose values will be retrieved
       * @param callback the callback to invoke upon change
       * @throws UnsupportedOperationException if the subscribe operation is not supported
       */
      default void subscribe(String path, Set<String> keys, ConfigChangeCallback callback) {
          throw new UnsupportedOperationException();
      }
  
      /**
       * Unsubscribes to changes for the given keys at the given path (optional operation).
       *
       * @param path the path where the data resides
       * @param keys the keys whose values will be retrieved
       * @param callback the callback to be unsubscribed from changes
       * @throws UnsupportedOperationException if the unsubscribe operation is not supported
       */
      default void unsubscribe(String path, Set<String> keys, ConfigChangeCallback callback) {
          throw new UnsupportedOperationException();
      }
  
      /**
       * Clears all subscribers (optional operation).
       *
       * @throws UnsupportedOperationException if the unsubscribeAll operation is not supported
       */
      default void unsubscribeAll() {
          throw new UnsupportedOperationException();
      }
  }
  