org.apache.hadoop.io

类 MapFile.Reader

java.lang.Object

org.apache.hadoop.io.MapFile.Reader

所有已实现的接口:

Closeable, AutoCloseable

直接已知子类:

ArrayFile.Reader, BloomMapFile.Reader, SetFile.Reader

封闭类:

MapFile

public static class MapFile.Reader
extends Object
implements Closeable

Provide access to an existing map.

构造器概要

构造器

限定符	构造器和说明
	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.
protected	MapFile.Reader(FileSystem fs, String dirName, WritableComparator comparator, Configuration conf, boolean open) Hook to allow subclasses to defer opening streams until further initialization is complete.

方法概要

方法

限定符和类型	方法和说明
void	close() Close the map.
protected SequenceFile.Reader	createDataFileReader(FileSystem fs, Path dataFile, Configuration conf) 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(FileSystem fs, String dirName, WritableComparator comparator, Configuration conf)
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.

从类继承的方法 java.lang.Object

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

构造器详细资料

MapFile.Reader

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

Construct a map reader for the named map.

抛出:

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.

抛出:

IOException

MapFile.Reader

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

Hook to allow subclasses to defer opening streams until further initialization is complete.

抛出:

IOException

另请参阅:

createDataFileReader(FileSystem, Path, Configuration)

方法详细资料

getKeyClass

public Class<?> getKeyClass()

Returns the class of keys in this file.

getValueClass

public Class<?> getValueClass()

Returns the class of values in this file.

open

protected void open(FileSystem fs,
        String dirName,
        WritableComparator comparator,
        Configuration conf)
             throws IOException

抛出:

IOException

createDataFileReader

protected SequenceFile.Reader createDataFileReader(FileSystem fs,
                                       Path dataFile,
                                       Configuration conf)
                                            throws IOException

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

抛出:

IOException

reset

public void reset()
           throws IOException

Re-positions the reader before its first key.

抛出:

IOException

midKey

public WritableComparable midKey()
                          throws IOException

Get the key at approximately the middle of the file.

抛出:

IOException

finalKey

public void finalKey(WritableComparable key)
              throws IOException

Reads the final key from the file.

参数:

key - key to read into

抛出:

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.

抛出:

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

抛出:

IOException

get

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

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

抛出:

IOException

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. - * @param key - key that we're trying to find - * @param val - data value if key is found - * @return - the key that was the closest match or null if eof.

抛出:

IOException

getClosest

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

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

参数:

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.

返回:

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

抛出:

IOException

close

public void close()
           throws IOException

Close the map.

指定者:

close 在接口中 Closeable

指定者:

close 在接口中 AutoCloseable

抛出:

IOException