001/**
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018
019package org.apache.hadoop.mapred;
020
021import java.io.IOException;
022
023import org.apache.hadoop.classification.InterfaceAudience;
024import org.apache.hadoop.classification.InterfaceStability;
025import org.apache.hadoop.fs.FileSystem;
026import org.apache.hadoop.util.Progressable;
027
028/** 
029 * <code>OutputFormat</code> describes the output-specification for a 
030 * Map-Reduce job.
031 *
032 * <p>The Map-Reduce framework relies on the <code>OutputFormat</code> of the
033 * job to:<p>
034 * <ol>
035 *   <li>
036 *   Validate the output-specification of the job. For e.g. check that the 
037 *   output directory doesn't already exist. 
038 *   <li>
039 *   Provide the {@link RecordWriter} implementation to be used to write out
040 *   the output files of the job. Output files are stored in a 
041 *   {@link FileSystem}.
042 *   </li>
043 * </ol>
044 * 
045 * @see RecordWriter
046 * @see JobConf
047 */
048@InterfaceAudience.Public
049@InterfaceStability.Stable
050public interface OutputFormat<K, V> {
051
052  /** 
053   * Get the {@link RecordWriter} for the given job.
054   *
055   * @param ignored
056   * @param job configuration for the job whose output is being written.
057   * @param name the unique name for this part of the output.
058   * @param progress mechanism for reporting progress while writing to file.
059   * @return a {@link RecordWriter} to write the output for the job.
060   * @throws IOException
061   */
062  RecordWriter<K, V> getRecordWriter(FileSystem ignored, JobConf job,
063                                     String name, Progressable progress)
064  throws IOException;
065
066  /** 
067   * Check for validity of the output-specification for the job.
068   *  
069   * <p>This is to validate the output specification for the job when it is
070   * a job is submitted.  Typically checks that it does not already exist,
071   * throwing an exception when it already exists, so that output is not
072   * overwritten.</p>
073   *
074   * @param ignored
075   * @param job job configuration.
076   * @throws IOException when output should not be attempted
077   */
078  void checkOutputSpecs(FileSystem ignored, JobConf job) throws IOException;
079}
080