Package org.apache.hadoop.io

Class SequenceFile.Reader

java.lang.Object

org.apache.hadoop.io.SequenceFile.Reader

All Implemented Interfaces:

java.io.Closeable, java.lang.AutoCloseable

Enclosing class:

SequenceFile

public static class SequenceFile.Reader
extends java.lang.Object
implements java.io.Closeable

Reads key/value pairs from a sequence-format file.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static interface	SequenceFile.Reader.Option	A tag interface for all of the Reader options

Constructor Summary

Constructors

Constructor	Description
Reader(Configuration conf, SequenceFile.Reader.Option... opts)
Reader(FileSystem fs, Path file, Configuration conf)	Deprecated. Use Reader(Configuration, Option...) instead.
Reader(FSDataInputStream in, int buffersize, long start, long length, Configuration conf)	Deprecated. Use Reader(Configuration, Reader.Option...) instead.

Method Summary

Modifier and Type	Method	Description
static SequenceFile.Reader.Option	bufferSize(int value)	Create an option with the buffer size for reading the given pathname.
void	close()	Close the file.
SequenceFile.ValueBytes	createValueBytes()
static SequenceFile.Reader.Option	file(Path value)	Create an option to specify the path name of the sequence file.
CompressionCodec	getCompressionCodec()	Returns the compression codec of data in this file.
SequenceFile.CompressionType	getCompressionType()	Get the compression type for this file.
java.lang.Object	getCurrentValue(java.lang.Object val)
void	getCurrentValue(Writable val)	Get the 'value' corresponding to the last read 'key'.
java.lang.Class<?>	getKeyClass()
java.lang.String	getKeyClassName()
SequenceFile.Metadata	getMetadata()	Returns the metadata object of the file.
long	getPosition()
java.lang.Class<?>	getValueClass()
java.lang.String	getValueClassName()
boolean	isBlockCompressed()	Returns true if records are block-compressed.
boolean	isCompressed()	Returns true if values are compressed.
static SequenceFile.Reader.Option	length(long value)	Create an option to specify the number of bytes to read.
java.lang.Object	next(java.lang.Object key)	Read the next key in the file, skipping its value.
boolean	next(Writable key)
boolean	next(Writable key, Writable val)	Read the next key/value pair in the file into key and val.
int	nextRaw(DataOutputBuffer key, SequenceFile.ValueBytes val)	Read 'raw' records.
int	nextRawKey(DataOutputBuffer key)	Read 'raw' keys.
int	nextRawValue(SequenceFile.ValueBytes val)	Read 'raw' values.
protected FSDataInputStream	openFile(FileSystem fs, Path file, int bufferSize, long length)	Override this method to specialize the type of FSDataInputStream returned.
void	seek(long position)	Set the current byte position in the input file.
static SequenceFile.Reader.Option	start(long value)	Create an option to specify the starting byte to read.
static SequenceFile.Reader.Option	stream(FSDataInputStream value)	Create an option to specify the stream with the sequence file.
void	sync(long position)	Seek to the next sync mark past a given position.
boolean	syncSeen()
java.lang.String	toString()	Returns the name of the file.

Methods inherited from class java.lang.Object

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

Constructor Detail

Reader

public Reader(Configuration conf,
              SequenceFile.Reader.Option... opts)
       throws java.io.IOException

Throws:

java.io.IOException

Reader

@Deprecated
public Reader(FileSystem fs,
              Path file,
              Configuration conf)
       throws java.io.IOException

Deprecated.

Use Reader(Configuration, Option...) instead.

Construct a reader by opening a file from the given file system.

Parameters:

fs - The file system used to open the file.

file - The file being read.

conf - Configuration

Throws:

java.io.IOException - raised on errors performing I/O.

Reader

@Deprecated
public Reader(FSDataInputStream in,
              int buffersize,
              long start,
              long length,
              Configuration conf)
       throws java.io.IOException

Deprecated.

Use Reader(Configuration, Reader.Option...) instead.

Construct a reader by the given input stream.

Parameters:

in - An input stream.

buffersize - unused

start - The starting position.

length - The length being read.

conf - Configuration

Throws:

java.io.IOException - raised on errors performing I/O.

Method Detail

file

public static SequenceFile.Reader.Option file(Path value)

Create an option to specify the path name of the sequence file.

Parameters:

value - the path to read

Returns:

a new option

stream

public static SequenceFile.Reader.Option stream(FSDataInputStream value)

Create an option to specify the stream with the sequence file.

Parameters:

value - the stream to read.

Returns:

a new option

start

public static SequenceFile.Reader.Option start(long value)

Create an option to specify the starting byte to read.

Parameters:

value - the number of bytes to skip over

Returns:

a new option

length

public static SequenceFile.Reader.Option length(long value)

Create an option to specify the number of bytes to read.

Parameters:

value - the number of bytes to read

Returns:

a new option

bufferSize

public static SequenceFile.Reader.Option bufferSize(int value)

Create an option with the buffer size for reading the given pathname.

Parameters:

value - the number of bytes to buffer

Returns:

a new option

openFile

protected FSDataInputStream openFile(FileSystem fs,
                                     Path file,
                                     int bufferSize,
                                     long length)
                              throws java.io.IOException

Override this method to specialize the type of FSDataInputStream returned.

Parameters:

fs - The file system used to open the file.

file - The file being read.

bufferSize - The buffer size used to read the file.

length - The length being read if it is >= 0. Otherwise, the length is not available.

Returns:

The opened stream.

Throws:

java.io.IOException - raised on errors performing I/O.

close

public void close()
           throws java.io.IOException

Close the file.

Specified by:

close in interface java.lang.AutoCloseable

Specified by:

close in interface java.io.Closeable

Throws:

java.io.IOException

getKeyClassName

public java.lang.String getKeyClassName()

Returns:

Returns the name of the key class.

getKeyClass

public java.lang.Class<?> getKeyClass()

Returns:

Returns the class of keys in this file.

getValueClassName

public java.lang.String getValueClassName()

Returns:

Returns the name of the value class.

getValueClass

public java.lang.Class<?> getValueClass()

Returns:

Returns the class of values in this file.

isCompressed

public boolean isCompressed()

Returns true if values are compressed.

Returns:

if values are compressed true, not false.

isBlockCompressed

public boolean isBlockCompressed()

Returns true if records are block-compressed.

Returns:

if records are block-compressed true, not false.

getCompressionCodec

public CompressionCodec getCompressionCodec()

Returns the compression codec of data in this file.

Returns:

CompressionCodec.

getCompressionType

public SequenceFile.CompressionType getCompressionType()

Get the compression type for this file.

Returns:

the compression type

getMetadata

public SequenceFile.Metadata getMetadata()

Returns the metadata object of the file.

Returns:

metadata.

getCurrentValue

public void getCurrentValue(Writable val)
                     throws java.io.IOException

Get the 'value' corresponding to the last read 'key'.

Parameters:

val - : The 'value' to be read.

Throws:

java.io.IOException - raised on errors performing I/O.

getCurrentValue

public java.lang.Object getCurrentValue(java.lang.Object val)
                                 throws java.io.IOException

Parameters:

val - : The 'value' to be read.

Returns:

Get the 'value' corresponding to the last read 'key'.

Throws:

java.io.IOException - raised on errors performing I/O.

next

public boolean next(Writable key)
             throws java.io.IOException

Parameters:

key - key.

Returns:

Read the next key in the file into key, skipping its value.True if another entry exists, and false at end of file.

Throws:

java.io.IOException - raised on errors performing I/O.

next

public boolean next(Writable key,
                    Writable val)
             throws java.io.IOException

Read the next key/value pair in the file into key and val.

Parameters:

key - input key.

val - input val.

Returns:

Returns true if such a pair exists and false when at end of file.

Throws:

java.io.IOException - raised on errors performing I/O.

createValueBytes

public SequenceFile.ValueBytes createValueBytes()

nextRaw

public int nextRaw(DataOutputBuffer key,
                   SequenceFile.ValueBytes val)
            throws java.io.IOException

Read 'raw' records.

Parameters:

key - - The buffer into which the key is read

val - - The 'raw' value

Returns:

Returns the total record length or -1 for end of file

Throws:

java.io.IOException - raised on errors performing I/O.

nextRawKey

public int nextRawKey(DataOutputBuffer key)
               throws java.io.IOException

Read 'raw' keys.

Parameters:

key - - The buffer into which the key is read

Returns:

Returns the key length or -1 for end of file

Throws:

java.io.IOException - raised on errors performing I/O.

next

public java.lang.Object next(java.lang.Object key)
                      throws java.io.IOException

Read the next key in the file, skipping its value.

Parameters:

key - input Object key.

Returns:

Return null at end of file.

Throws:

java.io.IOException - raised on errors performing I/O.

nextRawValue

public int nextRawValue(SequenceFile.ValueBytes val)
                 throws java.io.IOException

Read 'raw' values.

Parameters:

val - - The 'raw' value

Returns:

Returns the value length

Throws:

java.io.IOException - raised on errors performing I/O.

seek

public void seek(long position)
          throws java.io.IOException

Set the current byte position in the input file.

The position passed must be a position returned by SequenceFile.Writer.getLength() when writing this file. To seek to an arbitrary position, use sync(long).

Parameters:

position - input position.

Throws:

java.io.IOException - raised on errors performing I/O.

sync

public void sync(long position)
          throws java.io.IOException

Seek to the next sync mark past a given position.

Parameters:

position - position.

Throws:

java.io.IOException - raised on errors performing I/O.

syncSeen

public boolean syncSeen()

Returns:

Returns true iff the previous call to next passed a sync mark.

getPosition

public long getPosition()
                 throws java.io.IOException

Returns:

Return the current byte position in the input file.

Throws:

java.io.IOException - raised on errors performing I/O.

toString

public java.lang.String toString()

Returns the name of the file.

Overrides:

toString in class java.lang.Object