## org.apache.hadoop.mapreduce.lib.output
Class FileOutputFormat<K,V>

    java.lang.Object
      org.apache.hadoop.mapreduce.OutputFormat<K,V>
          org.apache.hadoop.mapreduce.lib.output.FileOutputFormat<K,V>

Direct Known Subclasses:
  SequenceFileOutputFormat, TextOutputFormat

    public abstract class FileOutputFormat<K,V>

extends OutputFormat<K,V>

A base class for `OutputFormat`s that read from `FileSystem`s.

Nested Class Summary
`static class` `FileOutputFormat.Counter`

Constructor Summary
`FileOutputFormat()`

Method Summary
`void` `checkOutputSpecs(JobContext job)` Check for validity of the output-specification for the job.
`static boolean` `getCompressOutput(JobContext job)` Is the job output compressed?
`Path` `getDefaultWorkFile(TaskAttemptContext context, String extension)` Get the default path and filename for the output format.
`OutputCommitter` `getOutputCommitter(TaskAttemptContext context)` Get the output committer for this output format.
`static Class<? extends CompressionCodec>` `getOutputCompressorClass(JobContext job, Class<? extends CompressionCodec> defaultValue)` Get the `CompressionCodec` for compressing the job outputs.
`static Path` `getOutputPath(JobContext job)` Get the `Path` to the output directory for the map-reduce job.
`static Path` `getPathForWorkFile(TaskInputOutputContext<?,?,?,?> context, String name, String extension)` Helper function to generate a `Path` for a file that is unique for the task within the job output directory.
`abstract RecordWriter<K,V>` `getRecordWriter(TaskAttemptContext job)` Get the `RecordWriter` for the given task.
`static String` `getUniqueFile(TaskAttemptContext context, String name, String extension)` Generate a unique filename, based on the task id, name, and extension

`static Path`

`getWorkOutputPath(TaskInputOutputContext<?,?,?,?> context)`
Get the `Path` to the task's temporary output directory for the map-reduce job

#### Tasks' Side-Effect Files

`static void` `setCompressOutput(Job job, boolean compress)` Set whether the output of the job is compressed.
`static void` `setOutputCompressorClass(Job job, Class<? extends CompressionCodec> codecClass)` Set the `CompressionCodec` to be used to compress job outputs.
`static void` `setOutputPath(Job job, Path outputDir)` Set the `Path` of the output directory for the map-reduce job.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### FileOutputFormat

    public FileOutputFormat()

Method Detail

### setCompressOutput

    public static void setCompressOutput(Job job,
                                         boolean compress)

  Set whether the output of the job is compressed.

  Parameters:
    `job` - the job to modify
    `compress` - should the output of the job be compressed?

### getCompressOutput

    public static boolean getCompressOutput(JobContext job)

  Is the job output compressed?

  Parameters:
    `job` - the Job to look in
  Returns:
    `true` if the job output should be compressed, `false` otherwise

### setOutputCompressorClass

    public static void setOutputCompressorClass(Job job,
                                                Class<? extends CompressionCodec> codecClass)

  Set the `CompressionCodec` to be used to compress job outputs.

  Parameters:
    `job` - the job to modify
    `codecClass` - the `CompressionCodec` to be used to compress the job outputs

### getOutputCompressorClass

    public static Class<? extends CompressionCodec> getOutputCompressorClass(JobContext job,
                                                                             Class<? extends CompressionCodec> defaultValue)

  Get the `CompressionCodec` for compressing the job outputs.

  Parameters:
    `job` - the `Job` to look in
    `defaultValue` - the `CompressionCodec` to return if not set
  Returns:
    the `CompressionCodec` to be used to compress the job outputs
  Throws:
    `IllegalArgumentException` - if the class was specified, but not found

### getRecordWriter

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

  Description copied from class: `OutputFormat`
  Get the `RecordWriter` for the given task.

  Specified by:
    `getRecordWriter` in class `OutputFormat<K,V>`
  Parameters:
    `job` - the information about the current task.
  Returns:
    a `RecordWriter` to write the output for the job.
  Throws:
    `IOException`
    `InterruptedException`

### checkOutputSpecs

    public void checkOutputSpecs(JobContext job)
                          throws FileAlreadyExistsException,
                                 IOException

  Description copied from class: `OutputFormat`
  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.

  Specified by:
    `checkOutputSpecs` in class `OutputFormat<K,V>`
  Parameters:
    `job` - information about the job
  Throws:
    `IOException` - when output should not be attempted
    `FileAlreadyExistsException`

### setOutputPath

    public static void setOutputPath(Job job,
                                     Path outputDir)

  Set the `Path` of the output directory for the map-reduce job.

  Parameters:
    `job` - The job to modify
    `outputDir` - the `Path` of the output directory for the map-reduce job.

### getOutputPath

    public static Path getOutputPath(JobContext job)

  Get the `Path` to the output directory for the map-reduce job.

  Returns:
    the `Path` to the output directory for the map-reduce job.
  See Also:
    `getWorkOutputPath(TaskInputOutputContext)`

### getWorkOutputPath

    public static Path getWorkOutputPath(TaskInputOutputContext<?,?,?,?> context)
                                  throws IOException,
                                         InterruptedException

  Get the `Path` to the task's temporary output directory for the map-reduce job

  #### Tasks' Side-Effect Files

  Some applications need to create/write-to side-files, which differ from the actual job-outputs.

  In such cases there could be issues with 2 instances of the same TIP (running simultaneously e.g. speculative tasks) trying to open/write-to the same file (path) on HDFS. Hence the application-writer will have to pick unique names per task-attempt (e.g. using the attemptid, say `attempt_200709221812_0001_m_000000_0`), not just per TIP.

  To get around this the Map-Reduce framework helps the application-writer out by maintaining a special `${mapred.output.dir}/_temporary/_${taskid}` sub-directory for each task-attempt on HDFS where the output of the task-attempt goes. On successful completion of the task-attempt the files in the `${mapred.output.dir}/_temporary/_${taskid}` (only) are promoted to `${mapred.output.dir}`. Of course, the framework discards the sub-directory of unsuccessful task-attempts. This is completely transparent to the application.

  The application-writer can take advantage of this by creating any side-files required in a work directory during execution of his task i.e. via `getWorkOutputPath(TaskInputOutputContext)`, and the framework will move them out similarly - thus she doesn't have to pick unique paths per task-attempt.

  The entire discussion holds true for maps of jobs with reducer=NONE (i.e. 0 reduces) since output of the map, in that case, goes directly to HDFS.

  Returns:
    the `Path` to the task's temporary output directory for the map-reduce job.
  Throws:
    `IOException`
    `InterruptedException`

### getPathForWorkFile

    public static Path getPathForWorkFile(TaskInputOutputContext<?,?,?,?> context,
                                          String name,
                                          String extension)
                                   throws IOException,
                                          InterruptedException

  Helper function to generate a `Path` for a file that is unique for the task within the job output directory.

  The path can be used to create custom files from within the map and reduce tasks. The path name will be unique for each task. The path parent will be the job output directory.

  ls

  This method uses the `getUniqueFile(org.apache.hadoop.mapreduce.TaskAttemptContext, java.lang.String, java.lang.String)` method to make the file name unique for the task.

  Parameters:
    `context` - the context for the task.
    `name` - the name for the file.
    `extension` - the extension for the file
  Returns:
    a unique path accross all tasks of the job.
  Throws:
    `IOException`
    `InterruptedException`

### getUniqueFile

    public static String getUniqueFile(TaskAttemptContext context,
                                       String name,
                                       String extension)

  Generate a unique filename, based on the task id, name, and extension

  Parameters:
    `context` - the task that is calling this
    `name` - the base filename
    `extension` - the filename extension
  Returns:
    a string like $name-[mr]-$id$extension

### getDefaultWorkFile

    public Path getDefaultWorkFile(TaskAttemptContext context,
                                   String extension)
                            throws IOException

  Get the default path and filename for the output format.

  Parameters:
    `context` - the task context
    `extension` - an extension to add to the filename
  Returns:
    a full path $output/_temporary/$taskid/part-[mr]-$id
  Throws:
    `IOException`

### getOutputCommitter

    public OutputCommitter getOutputCommitter(TaskAttemptContext context)
                                       throws IOException

  Description copied from class: `OutputFormat`
  Get the output committer for this output format. This is responsible for ensuring the output is committed correctly.

  Specified by:
    `getOutputCommitter` in class `OutputFormat<K,V>`
  Parameters:
    `context` - the task context
  Returns:
    an output committer
  Throws:
    `IOException`

Copyright © 2009 The Apache Software Foundation