org.apache.hadoop.hbase.io.hfile

Interface HFileScanner

All Superinterfaces:

AutoCloseable, Closeable, Shipper

All Known Implementing Classes:

HFileReaderImpl.EncodedScanner, HFileReaderImpl.HFileScannerImpl

@InterfaceAudience.Private
public interface HFileScanner
extends Shipper, Closeable

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(Cell) 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

Modifier and Type	Method and Description
void	close() Close this HFile scanner and do necessary cleanup.
Cell	getCell()
Cell	getKey() Gets the current key in the form of a cell.
String	getKeyString() Deprecated. Since hbase-2.0.0
Cell	getNextIndexedKey()
HFile.Reader	getReader()
ByteBuffer	getValue() Gets a buffer view to the current value.
String	getValueString() Deprecated. Since hbase-2.0.0
boolean	isSeeked()
boolean	next() Scans to the next entry in the file.
int	reseekTo(Cell cell) Reseek to or just before the passed cell.
boolean	seekBefore(Cell cell) Consider the cell stream of all the cells in the file, c[0] ..
boolean	seekTo() Positions this scanner at the start of the file.
int	seekTo(Cell cell) SeekTo or just before the passed cell.

Methods inherited from interface org.apache.hadoop.hbase.regionserver.Shipper

shipped

Method Detail

seekTo

int seekTo(Cell cell)
    throws IOException

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

Parameters:

cell -

Returns:

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

Throws:

IOException

reseekTo

int reseekTo(Cell cell)
      throws IOException

Reseek to or just before the passed cell. 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 cells which come after the current position of the scanner. Consider the cell stream of all the cells in the file, c[0] .. c[n], where there are n cellc in the file after current position of HFileScanner. The scanner will position itself between c[i] and c[i+1] where c[i] < cell <= c[i+1]. If there is no cell c[i+1] greater than or equal to the input cell, then the scanner will position itself at the end of the file and next() will return false when it is called.

Parameters:

cell - Cell to find (should be non-null)

Returns:

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

Throws:

IOException

seekBefore

boolean seekBefore(Cell cell)
            throws IOException

Consider the cell stream of all the cells in the file, c[0] .. c[n], where there are n cells in the file.

Parameters:

cell - Cell to find

Returns:

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

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

Cell getKey()

Gets the current key in the form of a cell. You must call seekTo(Cell) before this method.

Returns:

gets the current key as a Cell.

getValue

ByteBuffer getValue()

Gets a buffer view to the current value. You must call seekTo(Cell) 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.

getCell

Cell getCell()

Returns:

Instance of Cell.

getKeyString

@Deprecated
String getKeyString()

Deprecated. Since hbase-2.0.0

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

Returns:

key as a string

getValueString

@Deprecated
String getValueString()

Deprecated. Since hbase-2.0.0

Convenience method to get a copy of the value as a string - interpreting the bytes as UTF8. You must call seekTo(Cell) 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(Cell) or seekTo() or seekTo(Cell). Otherwise returns false.

getNextIndexedKey

Cell getNextIndexedKey()

Returns:

the next key in the index (the key to seek to the next block)

close

void close()

Close this HFile scanner and do necessary cleanup.

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Closeable