Package org.apache.nutch.tools.arc

Class ArcRecordReader

java.lang.Object

org.apache.hadoop.mapreduce.RecordReader<Text,BytesWritable>

org.apache.nutch.tools.arc.ArcRecordReader

All Implemented Interfaces:

Closeable, AutoCloseable

public class ArcRecordReader
extends RecordReader<Text,BytesWritable>

The ArchRecordReader class provides a record reader which reads records from arc files. Arc files are essentially tars of gzips. Each record in an arc file is a compressed gzip. Multiple records are concatenated together to form a complete arc. For more information on the arc file format

See Also:

• ArcFileFormat. Arc files are used by the Internet Archive and grub projects.
• archive.org
• grub.org

Field Summary

Fields

Modifier and Type	Field	Description
protected Configuration	conf
protected long	fileLen
protected FSDataInputStream	in
protected long	pos
protected long	splitEnd
protected long	splitLen
protected long	splitStart

Constructor Summary

Constructors

Constructor	Description
ArcRecordReader(Configuration conf, FileSplit split)	Constructor that sets the configuration and file split.

Method Summary

Modifier and Type	Method	Description
void	close()	Closes the record reader resources.
Text	createKey()	Creates a new instance of the Text object for the key.
BytesWritable	createValue()	Creates a new instance of the BytesWritable object for the key
Text	getCurrentKey()
BytesWritable	getCurrentValue()
long	getPos()	Returns the current position in the file.
float	getProgress()	Returns the percentage of progress in processing the file.
void	initialize(InputSplit split, TaskAttemptContext context)
static boolean	isMagic(byte[] input)	Returns true if the byte array passed matches the gzip header magic number.
boolean	next(Text key, BytesWritable value)	Returns true if the next record in the split is read into the key and value pair.
boolean	nextKeyValue()

Methods inherited from class java.lang.Object

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

Field Details

conf

protected Configuration conf

splitStart

protected long splitStart

pos

protected long pos

splitEnd

protected long splitEnd

splitLen

protected long splitLen

fileLen

protected long fileLen

in

protected FSDataInputStream in

Constructor Details

ArcRecordReader

public ArcRecordReader(Configuration conf,
 FileSplit split)
                throws IOException

Constructor that sets the configuration and file split.

Parameters:

conf - The job configuration.

split - The file split to read from.

Throws:

IOException - If an IO error occurs while initializing file split.

Method Details

isMagic

public static boolean isMagic(byte[] input)

Returns true if the byte array passed matches the gzip header magic number.

Parameters:

input - The byte array to check.

Returns:

True if the byte array matches the gzip header magic number.

close

public void close()
           throws IOException

Closes the record reader resources.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable

Specified by:

close in class RecordReader<Text,BytesWritable>

Throws:

IOException

createKey

public Text createKey()

Creates a new instance of the Text object for the key.

Returns:

Text

createValue

public BytesWritable createValue()

Creates a new instance of the BytesWritable object for the key

Returns:

BytesWritable

getPos

public long getPos()
            throws IOException

Returns the current position in the file.

Returns:

The long of the current position in the file.

Throws:

IOException - if there is a fatal I/O error reading the position within the FSDataInputStream

getProgress

public float getProgress()
                  throws IOException

Returns the percentage of progress in processing the file. This will be represented as a float from 0 to 1 with 1 being 100% completed.

Specified by:

getProgress in class RecordReader<Text,BytesWritable>

Returns:

The percentage of progress as a float from 0 to 1.

Throws:

IOException

getCurrentValue

public BytesWritable getCurrentValue()

Specified by:

getCurrentValue in class RecordReader<Text,BytesWritable>

getCurrentKey

public Text getCurrentKey()

Specified by:

getCurrentKey in class RecordReader<Text,BytesWritable>

nextKeyValue

public boolean nextKeyValue()

Specified by:

nextKeyValue in class RecordReader<Text,BytesWritable>

initialize

public void initialize(InputSplit split,
 TaskAttemptContext context)

Specified by:

initialize in class RecordReader<Text,BytesWritable>

next

public boolean next(Text key,
 BytesWritable value)
             throws IOException

Returns true if the next record in the split is read into the key and value pair. The key will be the arc record header and the values will be the raw content bytes of the arc record.

Parameters:

key - The record key

value - The record value

Returns:

True if the next record is read.

Throws:

IOException - If an error occurs while reading the record value.