Package com.healthmarketscience.jackcess.impl

Class PageChannel

java.lang.Object

com.healthmarketscience.jackcess.impl.PageChannel

All Implemented Interfaces:

Closeable, Flushable, AutoCloseable, Channel

public class PageChannel
extends Object
implements Channel, Flushable

Reads and writes individual pages in a database file

Author:

Tim McCune

Field Summary

Fields

Modifier and Type	Field	Description
static ByteOrder	DEFAULT_BYTE_ORDER	default byte order of access mdb files

Constructor Summary

Constructors

Constructor	Description
PageChannel(FileChannel channel, boolean closeChannel, JetFormat format, boolean autoSync)

Method Summary

Modifier and Type	Method	Description
int	allocateNewPage()	Allocates a new page in the database.
void	close()
static ByteBuffer	createBuffer(int size)
static ByteBuffer	createBuffer(int size, ByteOrder order)
ByteBuffer	createPageBuffer()
void	deallocatePage(int pageNumber)	Deallocate a previously used page in the database.
void	finishWrite()	Completes a "logical" write operation.
void	flush()
JetFormat	getFormat()
void	initialize(DatabaseImpl database, CodecProvider codecProvider)	Does second-stage initialization, must be called after construction.
boolean	isAutoSync()
boolean	isOpen()
boolean	isReuseFreePages()
boolean	isWriting()	Returns true if a logical write operation is in progress, false otherwise.
static ByteBuffer	narrowBuffer(ByteBuffer buffer, int position, int limit)
void	readPage(ByteBuffer buffer, int pageNumber)
void	readRootPage(ByteBuffer buffer)
void	setReuseFreePages(boolean reuseFreePages)
void	startExclusiveWrite()	Begins an exclusive "logical" write operation (throws an exception if another write operation is outstanding).
void	startWrite()	Begins a "logical" write operation.
int	truncateFreeSpace()	Shortens the file to drop the run of free pages at the end of it, and returns the number of pages it dropped.
static ByteBuffer	wrap(byte[] bytes)	Returns a ByteBuffer wrapping the given bytes and configured with the default byte order.
void	writePage(ByteBuffer page, int pageNumber)	Write a page to disk
void	writePage(ByteBuffer page, int pageNumber, int pageOffset)	Write a page (or part of a page) to disk

Methods inherited from class java.lang.Object

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

Field Detail

DEFAULT_BYTE_ORDER

public static final ByteOrder DEFAULT_BYTE_ORDER

default byte order of access mdb files

Constructor Detail

PageChannel

public PageChannel(FileChannel channel,
                   boolean closeChannel,
                   JetFormat format,
                   boolean autoSync)

Parameters:

channel - Channel containing the database

format - Format of the database in the channel

Method Detail

initialize

public void initialize(DatabaseImpl database,
                       CodecProvider codecProvider)
                throws IOException

Does second-stage initialization, must be called after construction.

Throws:

IOException

getFormat

public JetFormat getFormat()

isAutoSync

public boolean isAutoSync()

isReuseFreePages

public boolean isReuseFreePages()

setReuseFreePages

public void setReuseFreePages(boolean reuseFreePages)

startWrite

public void startWrite()

Begins a "logical" write operation. See finishWrite() for more details.

startExclusiveWrite

public void startExclusiveWrite()

Begins an exclusive "logical" write operation (throws an exception if another write operation is outstanding). See finishWrite() for more details.

finishWrite

public void finishWrite()
                 throws IOException

Completes a "logical" write operation. This method should be called in finally block which wraps a logical write operation (which is preceded by a startWrite() call). Logical write operations may be nested. If the database is configured for "auto-sync", the channel will be flushed when the outermost operation is complete,

Throws:

IOException

isWriting

public boolean isWriting()

Returns true if a logical write operation is in progress, false otherwise.

readPage

public void readPage(ByteBuffer buffer,
                     int pageNumber)
              throws IOException

Parameters:

buffer - Buffer to read the page into

pageNumber - Number of the page to read in (starting at 0)

Throws:

IOException

readRootPage

public void readRootPage(ByteBuffer buffer)
                  throws IOException

Parameters:

buffer - Buffer to read the root page into

Throws:

IOException

writePage

public void writePage(ByteBuffer page,
                      int pageNumber)
               throws IOException

Write a page to disk

Parameters:

page - Page to write

pageNumber - Page number to write the page to

Throws:

IOException

writePage

public void writePage(ByteBuffer page,
                      int pageNumber,
                      int pageOffset)
               throws IOException

Write a page (or part of a page) to disk

Parameters:

page - Page to write

pageNumber - Page number to write the page to

pageOffset - offset within the page at which to start writing the page data

Throws:

IOException

allocateNewPage

public int allocateNewPage()
                    throws IOException

Allocates a new page in the database. Data in the page is undefined until it is written in a call to writePage(ByteBuffer,int).

Throws:

IOException

truncateFreeSpace

public int truncateFreeSpace()
                      throws IOException

Shortens the file to drop the run of free pages at the end of it, and returns the number of pages it dropped. A file can be shortened only at its end, so this is the whole of what can be given back without rewriting the file.

Throws:

IOException

deallocatePage

public void deallocatePage(int pageNumber)
                    throws IOException

Deallocate a previously used page in the database.

Throws:

IOException

createPageBuffer

public ByteBuffer createPageBuffer()

Returns:

A newly-allocated buffer that can be passed to readPage

createBuffer

public static ByteBuffer createBuffer(int size)

Returns:

A newly-allocated buffer of the given size and DEFAULT_BYTE_ORDER byte order

createBuffer

public static ByteBuffer createBuffer(int size,
                                      ByteOrder order)

Returns:

A newly-allocated buffer of the given size and byte order

flush

public void flush()
           throws IOException

Specified by:

flush in interface Flushable

Throws:

IOException

close

public void close()
           throws IOException

Specified by:

close in interface AutoCloseable

Specified by:

close in interface Channel

Specified by:

close in interface Closeable

Throws:

IOException

isOpen

public boolean isOpen()

Specified by:

isOpen in interface Channel

narrowBuffer

public static ByteBuffer narrowBuffer(ByteBuffer buffer,
                                      int position,
                                      int limit)

Returns:

a duplicate of the current buffer narrowed to the given position and limit. mark will be set at the current position.

wrap

public static ByteBuffer wrap(byte[] bytes)

Returns a ByteBuffer wrapping the given bytes and configured with the default byte order.