org.apache.hadoop.io

Class MapFile.Reader

java.lang.Object

org.apache.hadoop.io.MapFile.Reader

All Implemented Interfaces:

Closeable, AutoCloseable

Direct Known Subclasses:

ArrayFile.Reader, BloomMapFile.Reader, SetFile.Reader

Enclosing class:

MapFile

public static class MapFile.Reader
extends Object
implements Closeable

Provide access to an existing map.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	MapFile.Reader.Option

Constructor Summary

Constructors

Constructor and Description
Reader(FileSystem fs, String dirName, Configuration conf) Deprecated.
Reader(FileSystem fs, String dirName, WritableComparator comparator, Configuration conf) Deprecated.
Reader(Path dir, Configuration conf, SequenceFile.Reader.Option... opts)

Method Summary

Modifier and Type	Method and Description
void	close() Close the map.
static MapFile.Reader.Option	comparator(WritableComparator value)
protected SequenceFile.Reader	createDataFileReader(Path dataFile, Configuration conf, SequenceFile.Reader.Option... options) Override this method to specialize the type of SequenceFile.Reader returned.
void	finalKey(WritableComparable key) Reads the final key from the file.
Writable	get(WritableComparable key, Writable val) Return the value for the named key, or null if none exists.
WritableComparable	getClosest(WritableComparable key, Writable val) Finds the record that is the closest match to the specified key.
WritableComparable	getClosest(WritableComparable key, Writable val, boolean before) Finds the record that is the closest match to the specified key.
Class<?>	getKeyClass() Returns the class of keys in this file.
Class<?>	getValueClass() Returns the class of values in this file.
WritableComparable	midKey() Get the key at approximately the middle of the file.
boolean	next(WritableComparable key, Writable val) Read the next key/value pair in the map into key and val.
protected void	open(Path dir, WritableComparator comparator, Configuration conf, SequenceFile.Reader.Option... options)
void	reset() Re-positions the reader before its first key.
boolean	seek(WritableComparable key) Positions the reader at the named key, or if none such exists, at the first entry after the named key.

Methods inherited from class java.lang.Object

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

Constructor Detail

Reader

public Reader(Path dir,
              Configuration conf,
              SequenceFile.Reader.Option... opts)
       throws IOException

Throws:

IOException

Reader

@Deprecated
public Reader(FileSystem fs,
                          String dirName,
                          Configuration conf)
                   throws IOException

Deprecated.

Construct a map reader for the named map.

Parameters:

fs - FileSystem.

dirName - dirName.

conf - configuration.

Throws:

IOException - raised on errors performing I/O.

Reader

@Deprecated
public Reader(FileSystem fs,
                          String dirName,
                          WritableComparator comparator,
                          Configuration conf)
                   throws IOException

Deprecated.

Construct a map reader for the named map using the named comparator.

Parameters:

fs - FileSystem.

dirName - dirName.

comparator - WritableComparator.

conf - Configuration.

Throws:

IOException - raised on errors performing I/O.

Method Detail

getKeyClass

public Class<?> getKeyClass()

Returns the class of keys in this file.

Returns:

keyClass.

getValueClass

public Class<?> getValueClass()

Returns the class of values in this file.

Returns:

Value Class.

comparator

public static MapFile.Reader.Option comparator(WritableComparator value)

open

protected void open(Path dir,
                    WritableComparator comparator,
                    Configuration conf,
                    SequenceFile.Reader.Option... options)
             throws IOException

Throws:

IOException

createDataFileReader

protected SequenceFile.Reader createDataFileReader(Path dataFile,
                                                   Configuration conf,
                                                   SequenceFile.Reader.Option... options)
                                            throws IOException

Override this method to specialize the type of SequenceFile.Reader returned.

Parameters:

dataFile - data file.

conf - configuration.

options - options.

Returns:

SequenceFile.Reader.

Throws:

IOException - raised on errors performing I/O.

reset

public void reset()
           throws IOException

Re-positions the reader before its first key.

Throws:

IOException - raised on errors performing I/O.

midKey

public WritableComparable midKey()
                          throws IOException

Get the key at approximately the middle of the file. Or null if the file is empty.

Returns:

WritableComparable.

Throws:

IOException - raised on errors performing I/O.

finalKey

public void finalKey(WritableComparable key)
              throws IOException

Reads the final key from the file.

Parameters:

key - key to read into

Throws:

IOException - raised on errors performing I/O.

seek

public boolean seek(WritableComparable key)
             throws IOException

Positions the reader at the named key, or if none such exists, at the first entry after the named key. Returns true iff the named key exists in this map.

Parameters:

key - key.

Returns:

if the named key exists in this map true, not false.

Throws:

IOException - raised on errors performing I/O.

next

public boolean next(WritableComparable key,
                    Writable val)
             throws IOException

Read the next key/value pair in the map into key and val. Returns true if such a pair exists and false when at the end of the map.

Parameters:

key - WritableComparable.

val - Writable.

Returns:

if such a pair exists true,not false.

Throws:

IOException - raised on errors performing I/O.

get

public Writable get(WritableComparable key,
                    Writable val)
             throws IOException

Return the value for the named key, or null if none exists.

Parameters:

key - key.

val - val.

Returns:

Writable if such a pair exists true,not false.

Throws:

IOException - raised on errors performing I/O.

getClosest

public WritableComparable getClosest(WritableComparable key,
                                     Writable val)
                              throws IOException

Finds the record that is the closest match to the specified key. Returns key or if it does not exist, at the first entry after the named key.

Parameters:

key - key that we're trying to find.

val - data value if key is found.

Returns:

the key that was the closest match or null if eof.

Throws:

IOException - raised on errors performing I/O.

getClosest

public WritableComparable getClosest(WritableComparable key,
                                     Writable val,
                                     boolean before)
                              throws IOException

Finds the record that is the closest match to the specified key.

Parameters:

key - - key that we're trying to find

val - - data value if key is found

before - - IF true, and key does not exist, return the first entry that falls just before the key. Otherwise, return the record that sorts just after.

Returns:

- the key that was the closest match or null if eof.

Throws:

IOException - raised on errors performing I/O.

close

public void close()
           throws IOException

Close the map.

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Throws:

IOException - raised on errors performing I/O.