org.apache.hadoop.mapred.lib

Class MultipleOutputFormat<K,V>

java.lang.Object

org.apache.hadoop.mapred.FileOutputFormat<K,V>

org.apache.hadoop.mapred.lib.MultipleOutputFormat<K,V>

All Implemented Interfaces:

OutputFormat<K,V>

Direct Known Subclasses:

MultipleSequenceFileOutputFormat, MultipleTextOutputFormat

@InterfaceAudience.Public
 @InterfaceStability.Stable
public abstract class MultipleOutputFormat<K,V>
extends FileOutputFormat<K,V>

This abstract class extends the FileOutputFormat, allowing to write the output data to different output files. There are three basic use cases for this class. Case one: This class is used for a map reduce job with at least one reducer. The reducer wants to write data to different files depending on the actual keys. It is assumed that a key (or value) encodes the actual key (value) and the desired location for the actual key (value). Case two: This class is used for a map only job. The job wants to use an output file name that is either a part of the input file name of the input data, or some derivation of it. Case three: This class is used for a map only job. The job wants to use an output file name that depends on both the keys and the input file name,

Constructor Summary

Constructors

Constructor and Description
MultipleOutputFormat()

Method Summary

Modifier and Type	Method and Description
protected K	generateActualKey(K key, V value) Generate the actual key from the given key/value.
protected V	generateActualValue(K key, V value) Generate the actual value from the given key and value.
protected String	generateFileNameForKeyValue(K key, V value, String name) Generate the file output file name based on the given key and the leaf file name.
protected String	generateLeafFileName(String name) Generate the leaf name for the output file name.
protected abstract RecordWriter<K,V>	getBaseRecordWriter(FileSystem fs, JobConf job, String name, Progressable arg3)
protected String	getInputFileBasedOutputFileName(JobConf job, String name) Generate the outfile name based on a given name and the input file name.
RecordWriter<K,V>	getRecordWriter(FileSystem fs, JobConf job, String name, Progressable arg3) Create a composite record writer that can write key/value data to different output files

Methods inherited from class org.apache.hadoop.mapred.FileOutputFormat

checkOutputSpecs, getCompressOutput, getOutputCompressorClass, getOutputPath, getPathForCustomFile, getTaskOutputPath, getUniqueName, getWorkOutputPath, setCompressOutput, setOutputCompressorClass, setOutputPath

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

MultipleOutputFormat

public MultipleOutputFormat()

Method Detail

getRecordWriter

public RecordWriter<K,V> getRecordWriter(FileSystem fs,
                                         JobConf job,
                                         String name,
                                         Progressable arg3)
                                  throws IOException

Create a composite record writer that can write key/value data to different output files

Specified by:

getRecordWriter in interface OutputFormat<K,V>

Specified by:

getRecordWriter in class FileOutputFormat<K,V>

Parameters:

fs - the file system to use

job - the job conf for the job

name - the leaf file name for the output file (such as part-00000")

arg3 - a progressable for reporting progress.

Returns:

a composite record writer

Throws:

IOException

generateLeafFileName

protected String generateLeafFileName(String name)

Generate the leaf name for the output file name. The default behavior does not change the leaf file name (such as part-00000)

Parameters:

name - the leaf file name for the output file

Returns:

the given leaf file name

generateFileNameForKeyValue

protected String generateFileNameForKeyValue(K key,
                                             V value,
                                             String name)

Generate the file output file name based on the given key and the leaf file name. The default behavior is that the file name does not depend on the key.

Parameters:

key - the key of the output data

name - the leaf file name

Returns:

generated file name

generateActualKey

protected K generateActualKey(K key,
                              V value)

Generate the actual key from the given key/value. The default behavior is that the actual key is equal to the given key

Parameters:

key - the key of the output data

value - the value of the output data

Returns:

the actual key derived from the given key/value

generateActualValue

protected V generateActualValue(K key,
                                V value)

Generate the actual value from the given key and value. The default behavior is that the actual value is equal to the given value

Parameters:

key - the key of the output data

value - the value of the output data

Returns:

the actual value derived from the given key/value

getInputFileBasedOutputFileName

protected String getInputFileBasedOutputFileName(JobConf job,
                                                 String name)

Generate the outfile name based on a given name and the input file name. If the MRJobConfig.MAP_INPUT_FILE does not exists (i.e. this is not for a map only job), the given name is returned unchanged. If the config value for "num.of.trailing.legs.to.use" is not set, or set 0 or negative, the given name is returned unchanged. Otherwise, return a file name consisting of the N trailing legs of the input file name where N is the config value for "num.of.trailing.legs.to.use".

Parameters:

job - the job config

name - the output file name

Returns:

the outfile name based on a given name and the input file name.

getBaseRecordWriter

protected abstract RecordWriter<K,V> getBaseRecordWriter(FileSystem fs,
                                                         JobConf job,
                                                         String name,
                                                         Progressable arg3)
                                                  throws IOException

Parameters:

fs - the file system to use

job - a job conf object

name - the name of the file over which a record writer object will be constructed

arg3 - a progressable object

Returns:

A RecordWriter object over the given file

Throws:

IOException