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

java.lang.Object
  extended by org.apache.hadoop.mapreduce.OutputFormat<K,V>
Direct Known Subclasses:
DBOutputFormat, FileOutputFormat, FilterOutputFormat, NullOutputFormat

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
OutputFormat()
           
 
Method Summary
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.

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


Copyright © 2009 The Apache Software Foundation