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.kstream;
  
  import org.apache.kafka.streams.KeyValue;
  import org.apache.kafka.streams.errors.StreamsException;
  import org.apache.kafka.streams.processor.ProcessorContext;
  import org.apache.kafka.streams.processor.PunctuationType;
  import org.apache.kafka.streams.processor.Punctuator;
  import org.apache.kafka.streams.processor.StateStore;
  import org.apache.kafka.streams.processor.To;
  import org.apache.kafka.streams.processor.api.FixedKeyProcessor;
  
  import java.time.Duration;
  
  /**
   * The {@code ValueTransformer} interface for stateful mapping of a value to a new value (with possible new type).
   * This is a stateful record-by-record operation, i.e, {@link #transform(Object)} is invoked individually for each
   * record of a stream and can access and modify a state that is available beyond a single call of
   * {@link #transform(Object)} (cf. {@link ValueMapper} for stateless value transformation).
   * Additionally, this {@code ValueTransformer} can {@link ProcessorContext#schedule(Duration, PunctuationType, Punctuator) schedule}
   * a method to be {@link Punctuator#punctuate(long) called periodically} with the provided context.
   * If {@code ValueTransformer} is applied to a {@link KeyValue} pair record the record's key is preserved.
   * <p>
   * Use {@link ValueTransformerSupplier} to provide new instances of {@code ValueTransformer} to Kafka Stream's runtime.
   * <p>
   * If a record's key and value should be modified {@link Transformer} can be used.
   *
   * @param <V>  value type
   * @param <VR> transformed value type
   * @see ValueTransformerSupplier
   * @see ValueTransformerWithKeySupplier
   * @see KTable#transformValues(ValueTransformerWithKeySupplier, Materialized, String...)
   * @see Transformer
   * @deprecated Since 4.0. Use {@link FixedKeyProcessor} instead.
   */
  @Deprecated
  public interface ValueTransformer<V, VR> {
  
      /**
       * Initialize this transformer.
       * This is called once per instance when the topology gets initialized.
       * When the framework is done with the transformer, {@link #close()} will be called on it; the
       * framework may later re-use the transformer by calling {@link #init(ProcessorContext)} again.
       * <p>
       * The provided {@link ProcessorContext context} can be used to access topology and record meta data, to
       * {@link ProcessorContext#schedule(Duration, PunctuationType, Punctuator) schedule} a method to be
       * {@link Punctuator#punctuate(long) called periodically} and to access attached {@link StateStore}s.
       * <p>
       * Note that {@link ProcessorContext} is updated in the background with the current record's meta data.
       * Thus, it only contains valid record meta data when accessed within {@link #transform(Object)}.
       * <p>
       * Note that using {@link ProcessorContext#forward(Object, Object)} or
       * {@link ProcessorContext#forward(Object, Object, To)} is not allowed within any method of
       * {@code ValueTransformer} and will result in an {@link StreamsException exception}.
       *
       * @param context the context
       * @throws IllegalStateException If store gets registered after initialization is already finished
       * @throws StreamsException if the store's change log does not contain the partition
       */
      void init(final ProcessorContext context);
  
      /**
       * Transform the given value to a new value.
       * Additionally, any {@link StateStore} that is {@link KTable#transformValues(ValueTransformerWithKeySupplier, String...)
       * attached} to this operator can be accessed and modified arbitrarily (cf.
       * {@link ProcessorContext#getStateStore(String)}).
       * <p>
       * Note, that using {@link ProcessorContext#forward(Object, Object)} or
       * {@link ProcessorContext#forward(Object, Object, To)} is not allowed within {@code transform} and
       * will result in an {@link StreamsException exception}.
       *
       * @param value the value to be transformed
       * @return the new value
       */
      VR transform(final V value);
  
      /**
       * Close this transformer and clean up any resources. The framework may
       * later re-use this transformer by calling {@link #init(ProcessorContext)} on it again.
       * <p>
       * It is not possible to return any new output records within {@code close()}.
       * Using {@link ProcessorContext#forward(Object, Object)} or {@link ProcessorContext#forward(Object, Object, To)}
       * will result in an {@link StreamsException exception}.
       */
      void close();
  
  }
  