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.connect.transforms;
  
  import org.apache.kafka.common.Configurable;
  import org.apache.kafka.common.config.ConfigDef;
  import org.apache.kafka.connect.connector.ConnectRecord;
  
  import java.io.Closeable;
  
  /**
   * Single message transformation for Kafka Connect record types.
   * <p>
   * Connectors can be configured with transformations to make lightweight message-at-a-time modifications.
   * <p>Kafka Connect may discover 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.connect.transforms.Transformation}.
   *
   * <p>Implement {@link org.apache.kafka.common.metrics.Monitorable} to enable the transformation to register metrics.
   * The following tags are automatically added to all metrics registered: <code>connector</code> set to connector name,
   * <code>task</code> set to the task id and <code>transformation</code> set to the transformation alias.
   *
   * @param <R> The type of record (must be an implementation of {@link ConnectRecord})
   */
  public interface Transformation<R extends ConnectRecord<R>> extends Configurable, Closeable {
  
      /**
       * Apply transformation to the {@code record} and return another record object (which may be {@code record} itself)
       * or {@code null}, corresponding to a map or filter operation respectively.
       * <p>
       * A transformation must not mutate objects reachable from the given {@code record}
       * (including, but not limited to, {@link org.apache.kafka.connect.header.Headers Headers},
       * {@link org.apache.kafka.connect.data.Struct Structs}, {@code Lists}, and {@code Maps}).
       * If such objects need to be changed, a new {@link ConnectRecord} should be created and returned.
       * <p>
       * The implementation must be thread-safe.
       *
       * @param record the record to be transformed; may not be null
       * @return the transformed record; may be null to indicate that the record should be dropped
       */
      R apply(R record);
  
      /** Configuration specification for this transformation. */
      ConfigDef config();
  
      /** Signal that this transformation instance will no longer will be used. */
      @Override
      void close();
  
  }
  