org.apache.hadoop.io
Class MapFile.Reader

java.lang.Object
  org.apache.hadoop.io.MapFile.Reader

Direct Known Subclasses:

ArrayFile.Reader, SetFile.Reader

Enclosing class:

MapFile

public static class MapFile.Reader
extends Object

Provide access to an existing map.

Constructor Summary

MapFile.Reader(FileSystem fs, String dirName, Configuration conf)
Construct a map reader for the named map.

MapFile.Reader(FileSystem fs, String dirName, WritableComparator comparator, Configuration conf)
Construct a map reader for the named map using the named comparator.

Method Summary

void	close() Close the map.
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.
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.
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

MapFile.Reader

public MapFile.Reader(FileSystem fs,
                      String dirName,
                      Configuration conf)
               throws IOException

Construct a map reader for the named map.

Throws:

IOException

MapFile.Reader

public MapFile.Reader(FileSystem fs,
                      String dirName,
                      WritableComparator comparator,
                      Configuration conf)
               throws IOException

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

Throws:

IOException

Method Detail

getKeyClass

public Class getKeyClass()

Returns the class of keys in this file.

getValueClass

public Class getValueClass()

Returns the class of values in this file.

reset

public void reset()
           throws IOException

Re-positions the reader before its first key.

Throws:

IOException

midKey

public WritableComparable midKey()
                          throws IOException

Get the key at approximately the middle of the file.

Throws:

IOException

finalKey

public void finalKey(WritableComparable key)
              throws IOException

Reads the final key from the file.

Parameters:

key - key to read into

Throws:

IOException

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.

Throws:

IOException

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

Throws:

IOException

get

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

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

Throws:

IOException

getClosest

public WritableComparable getClosest(WritableComparable key,
                                     Writable val)
                              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

Returns:

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

Throws:

IOException

close

public void close()
           throws IOException

Close the map.

Throws:

IOException