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.streams.processor;
  
  import org.apache.kafka.streams.Topology;
  import org.apache.kafka.streams.kstream.KStream;
  import org.apache.kafka.streams.kstream.Named;
  import org.apache.kafka.streams.processor.api.FixedKeyProcessorSupplier;
  import org.apache.kafka.streams.state.StoreBuilder;
  
  import java.util.Set;
  
  /**
   * Provides a set of {@link StoreBuilder}s that will be automatically added to the topology and connected to the
   * associated processor.
   * <p>
   * Implementing this interface is recommended when the associated processor wants to encapsulate its usage of its state
   * stores, rather than exposing them to the user building the topology.
   * <p>
   * In the event that separate but related processors may want to share the same store, different {@link ConnectedStoreProvider}s
   * may provide the same instance of {@link StoreBuilder}, as shown below.
   * <pre>{@code
   * class StateSharingProcessors {
   *     StoreBuilder<KeyValueStore<String, String>> storeBuilder =
   *         Stores.keyValueStoreBuilder(Stores.persistentKeyValueStore("myStore"), Serdes.String(), Serdes.String());
   *
   *     class SupplierA implements ProcessorSupplier<String, Integer> {
   *         Processor<String, Integer> get() {
   *             return new Processor() {
   *                 private StateStore store;
   *
   *                 void init(ProcessorContext context) {
   *                     this.store = context.getStateStore("myStore");
   *                 }
   *
   *                 void process(String key, Integer value) {
   *                     // can access this.store
   *                 }
   *
   *                 void close() {
   *                     // can access this.store
   *                 }
   *             }
   *         }
   *
   *         Set<StoreBuilder<?>> stores() {
   *             return Collections.singleton(storeBuilder);
   *         }
   *     }
   *
   *     class SupplierB implements ProcessorSupplier<String, String> {
   *         Processor<String, String> get() {
   *             return new Processor() {
   *                 private StateStore store;
   *
   *                 void init(ProcessorContext context) {
   *                     this.store = context.getStateStore("myStore");
   *                 }
   *
   *                 void process(String key, String value) {
   *                     // can access this.store
   *                 }
   *
   *                 void close() {
   *                     // can access this.store
   *                 }
   *             }
   *         }
   *
   *         Set<StoreBuilder<?>> stores() {
   *             return Collections.singleton(storeBuilder);
   *         }
   *     }
   * }
   * }</pre>
   *
   * @see Topology#addProcessor(String, org.apache.kafka.streams.processor.api.ProcessorSupplier, String...)
   * @see KStream#process(org.apache.kafka.streams.processor.api.ProcessorSupplier, String...)
   * @see KStream#process(org.apache.kafka.streams.processor.api.ProcessorSupplier, Named, String...)
   * @see KStream#processValues(FixedKeyProcessorSupplier, String...)
   * @see KStream#processValues(FixedKeyProcessorSupplier, Named, String...)
   */
  public interface ConnectedStoreProvider {
  
      /**
       * @return the state stores to be connected and added, or null if no stores should be automatically connected and added.
       */
      default Set<StoreBuilder<?>> stores() {
          return null;
      }
  }