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.mapreduce; 020 021import java.io.IOException; 022 023import org.apache.hadoop.classification.InterfaceAudience; 024import org.apache.hadoop.classification.InterfaceStability; 025import org.apache.hadoop.fs.FileSystem; 026 027/** 028 * <code>OutputFormat</code> describes the output-specification for a 029 * Map-Reduce job. 030 * 031 * <p>The Map-Reduce framework relies on the <code>OutputFormat</code> of the 032 * job to:<p> 033 * <ol> 034 * <li> 035 * Validate the output-specification of the job. For e.g. check that the 036 * output directory doesn't already exist. 037 * <li> 038 * Provide the {@link RecordWriter} implementation to be used to write out 039 * the output files of the job. Output files are stored in a 040 * {@link FileSystem}. 041 * </li> 042 * </ol> 043 * 044 * @see RecordWriter 045 */ 046@InterfaceAudience.Public 047@InterfaceStability.Stable 048public abstract class OutputFormat<K, V> { 049 050 /** 051 * Get the {@link RecordWriter} for the given task. 052 * 053 * @param context the information about the current task. 054 * @return a {@link RecordWriter} to write the output for the job. 055 * @throws IOException 056 */ 057 public abstract RecordWriter<K, V> 058 getRecordWriter(TaskAttemptContext context 059 ) throws IOException, InterruptedException; 060 061 /** 062 * Check for validity of the output-specification for the job. 063 * 064 * <p>This is to validate the output specification for the job when it is 065 * a job is submitted. Typically checks that it does not already exist, 066 * throwing an exception when it already exists, so that output is not 067 * overwritten.</p> 068 * 069 * @param context information about the job 070 * @throws IOException when output should not be attempted 071 */ 072 public abstract void checkOutputSpecs(JobContext context 073 ) throws IOException, 074 InterruptedException; 075 076 /** 077 * Get the output committer for this output format. This is responsible 078 * for ensuring the output is committed correctly. 079 * @param context the task context 080 * @return an output committer 081 * @throws IOException 082 * @throws InterruptedException 083 */ 084 public abstract 085 OutputCommitter getOutputCommitter(TaskAttemptContext context 086 ) throws IOException, InterruptedException; 087} 088