org.apache.hadoop.mapreduce

Class OutputFormat<K,V>

java.lang.Object

org.apache.hadoop.mapreduce.OutputFormat<K,V>

Direct Known Subclasses:

DBOutputFormat, FileOutputFormat, FilterOutputFormat, NullOutputFormat

@InterfaceAudience.Public
 @InterfaceStability.Stable
public abstract class OutputFormat<K,V>
extends Object

OutputFormat describes the output-specification for a Map-Reduce job.

The Map-Reduce framework relies on the OutputFormat of the job to:

1. Validate the output-specification of the job. For e.g. check that the output directory doesn't already exist.
2. Provide the RecordWriter implementation to be used to write out the output files of the job. Output files are stored in a FileSystem.

See Also:

RecordWriter

Constructor Summary

Constructors

Constructor and Description
OutputFormat()

Method Summary

Modifier and Type	Method and Description
abstract void	checkOutputSpecs(JobContext context) Check for validity of the output-specification for the job.
abstract OutputCommitter	getOutputCommitter(TaskAttemptContext context) Get the output committer for this output format.
abstract RecordWriter<K,V>	getRecordWriter(TaskAttemptContext context) Get the RecordWriter for the given task.

Methods inherited from class java.lang.Object

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

Constructor Detail

OutputFormat

public OutputFormat()

Method Detail

getRecordWriter

public abstract RecordWriter<K,V> getRecordWriter(TaskAttemptContext context)
                                           throws IOException,
                                                  InterruptedException

Get the RecordWriter for the given task.

Parameters:

context - the information about the current task.

Returns:

a RecordWriter to write the output for the job.

Throws:

IOException

InterruptedException

checkOutputSpecs

public abstract void checkOutputSpecs(JobContext context)
                               throws IOException,
                                      InterruptedException

Check for validity of the output-specification for the job.

This is to validate the output specification for the job when it is a job is submitted. Typically checks that it does not already exist, throwing an exception when it already exists, so that output is not overwritten.

Implementations which write to filesystems which support delegation tokens usually collect the tokens for the destination path(s) and attach them to the job context's JobConf.

Parameters:

context - information about the job

Throws:

IOException - when output should not be attempted

InterruptedException

getOutputCommitter

public abstract OutputCommitter getOutputCommitter(TaskAttemptContext context)
                                            throws IOException,
                                                   InterruptedException

Get the output committer for this output format. This is responsible for ensuring the output is committed correctly.

Parameters:

context - the task context

Returns:

an output committer

Throws:

IOException

InterruptedException