crunch-core/src/main/java/org/apache/crunch/types/Converter.java

/**
 * 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.crunch.types;

import java.io.Serializable;

import org.apache.crunch.DoFn;

/**
 * Converts the input key/value from a MapReduce task into the input to a
 * {@link DoFn}, or takes the output of a {@code DoFn} and write it to the
 * output key/values.
 */
public interface Converter<K, V, S, T> extends Serializable {
  S convertInput(K key, V value);

  T convertIterableInput(K key, Iterable<V> value);

  K outputKey(S value);

  V outputValue(S value);

  Class<K> getKeyClass();

  Class<V> getValueClass();

  /**
   * If true, convert the inputs or outputs from this {@code Converter} instance
   * before (for outputs) or after (for inputs) using the associated PType#getInputMapFn
   * and PType#getOutputMapFn calls.
   */
  boolean applyPTypeTransforms();
}