org.apache.hadoop.hbase.io.hfile

Interface HFileScanner

All Known Implementing Classes:

AbstractHFileReader.Scanner, HFileReaderV2.AbstractScannerV2, HFileReaderV2.EncodedScannerV2, HFileReaderV2.ScannerV2, HFileReaderV3.EncodedScannerV3, HFileReaderV3.ScannerV3

@InterfaceAudience.Private
public interface HFileScanner

A scanner allows you to position yourself within a HFile and scan through it. It allows you to reposition yourself as well.

A scanner doesn't always have a key/value that it is pointing to when it is first created and before seekTo()/seekTo(byte[]) are called. In this case, getKey()/getValue() returns null. At most other times, a key and value will be available. The general pattern is that you position the Scanner using the seekTo variants and then getKey and getValue.

Method Summary

Methods

Modifier and Type	Method and Description
ByteBuffer	getKey() Gets a buffer view to the current key.
String	getKeyString() Convenience method to get a copy of the key as a string - interpreting the bytes as UTF8.
KeyValue	getKeyValue()
HFile.Reader	getReader()
ByteBuffer	getValue() Gets a buffer view to the current value.
String	getValueString() Convenience method to get a copy of the value as a string - interpreting the bytes as UTF8.
boolean	isSeeked()
boolean	next() Scans to the next entry in the file.
int	reseekTo(byte[] key) Reseek to or just before the passed key.
int	reseekTo(byte[] key, int offset, int length)
boolean	seekBefore(byte[] key) Consider the key stream of all the keys in the file, k[0] ..
boolean	seekBefore(byte[] key, int offset, int length)
boolean	seekTo() Positions this scanner at the start of the file.
int	seekTo(byte[] key) SeekTo or just before the passed key.
int	seekTo(byte[] key, int offset, int length)

Method Detail

seekTo

int seekTo(byte[] key)
           throws IOException

SeekTo or just before the passed key. Examine the return code to figure whether we found the key or not. Consider the key stream of all the keys in the file, k[0] .. k[n], where there are n keys in the file.

Parameters:

key - Key to find.

Returns:

-1, if key < k[0], no position; 0, such that k[i] = key and scanner is left in position i; and 1, such that k[i] < key, and scanner is left in position i. The scanner will position itself between k[i] and k[i+1] where k[i] < key <= k[i+1]. If there is no key k[i+1] greater than or equal to the input key, then the scanner will position itself at the end of the file and next() will return false when it is called.

Throws:

IOException

seekTo

int seekTo(byte[] key,
         int offset,
         int length)
           throws IOException

Throws:

IOException

reseekTo

int reseekTo(byte[] key)
             throws IOException

Reseek to or just before the passed key. Similar to seekTo except that this can be called even if the scanner is not at the beginning of a file. This can be used to seek only to keys which come after the current position of the scanner. Consider the key stream of all the keys in the file, k[0] .. k[n], where there are n keys in the file after current position of HFileScanner. The scanner will position itself between k[i] and k[i+1] where k[i] < key <= k[i+1]. If there is no key k[i+1] greater than or equal to the input key, then the scanner will position itself at the end of the file and next() will return false when it is called.

Parameters:

key - Key to find (should be non-null)

Returns:

-1, if key < k[0], no position; 0, such that k[i] = key and scanner is left in position i; and 1, such that k[i] < key, and scanner is left in position i.

Throws:

IOException

reseekTo

int reseekTo(byte[] key,
           int offset,
           int length)
             throws IOException

Throws:

IOException

seekBefore

boolean seekBefore(byte[] key)
                   throws IOException

Consider the key stream of all the keys in the file, k[0] .. k[n], where there are n keys in the file.

Parameters:

key - Key to find

Returns:

false if key <= k[0] or true with scanner in position 'i' such that: k[i] < key. Furthermore: there may be a k[i+1], such that k[i] < key <= k[i+1] but there may also NOT be a k[i+1], and next() will return false (EOF).

Throws:

IOException

seekBefore

boolean seekBefore(byte[] key,
                 int offset,
                 int length)
                   throws IOException

Throws:

IOException

seekTo

boolean seekTo()
               throws IOException

Positions this scanner at the start of the file.

Returns:

False if empty file; i.e. a call to next would return false and the current key and value are undefined.

Throws:

IOException

next

boolean next()
             throws IOException

Scans to the next entry in the file.

Returns:

Returns false if you are at the end otherwise true if more in file.

Throws:

IOException

getKey

ByteBuffer getKey()

Gets a buffer view to the current key. You must call seekTo(byte[]) before this method.

Returns:

byte buffer for the key. The limit is set to the key size, and the position is 0, the start of the buffer view.

getValue

ByteBuffer getValue()

Gets a buffer view to the current value. You must call seekTo(byte[]) before this method.

Returns:

byte buffer for the value. The limit is set to the value size, and the position is 0, the start of the buffer view.

getKeyValue

KeyValue getKeyValue()

Returns:

Instance of KeyValue.

getKeyString

String getKeyString()

Convenience method to get a copy of the key as a string - interpreting the bytes as UTF8. You must call seekTo(byte[]) before this method.

Returns:

key as a string

getValueString

String getValueString()

Convenience method to get a copy of the value as a string - interpreting the bytes as UTF8. You must call seekTo(byte[]) before this method.

Returns:

value as a string

getReader

HFile.Reader getReader()

Returns:

Reader that underlies this Scanner instance.

isSeeked

boolean isSeeked()

Returns:

True is scanner has had one of the seek calls invoked; i.e. seekBefore(byte[]) or seekTo() or seekTo(byte[]). Otherwise returns false.