/**
* 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.hadoop.mapreduce;
import java.io.IOException;
import java.util.List;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
/**
* InputFormat
describes the input-specification for a
* Map-Reduce job.
*
*
The Map-Reduce framework relies on the InputFormat
of the
* job to:
*
InputSplit
for processing by
* the {@link Mapper}.
* The default behavior of file-based {@link InputFormat}s, typically * sub-classes of {@link FileInputFormat}, is to split the * input into logical {@link InputSplit}s based on the total size, in * bytes, of the input files. However, the {@link FileSystem} blocksize of * the input files is treated as an upper bound for input splits. A lower bound * on the split size can be set via * * mapred.min.split.size.
* *Clearly, logical splits based on input-size is insufficient for many
* applications since record boundaries are to respected. In such cases, the
* application has to also implement a {@link RecordReader} on whom lies the
* responsibility to respect record-boundaries and present a record-oriented
* view of the logical Each {@link InputSplit} is then assigned to an individual {@link Mapper}
* for processing. Note: The split is a logical split of the inputs and the
* input files are not physically split into chunks. For e.g. a split could
* be <input-file-path, start, offset> tuple. The InputFormat
* also creates the {@link RecordReader} to read the {@link InputSplit}.
*
* @param context job configuration.
* @return an array of {@link InputSplit}s for the job.
*/
public abstract
ListInputSplit
to the individual task.
*
* @see InputSplit
* @see RecordReader
* @see FileInputFormat
*/
public abstract class InputFormat