PageChannel

java.lang.Object
- com.healthmarketscience.jackcess.impl.PageChannel

All Implemented Interfaces:

java.io.Closeable, java.io.Flushable, java.lang.AutoCloseable, java.nio.channels.Channel
```
public class PageChannel
extends java.lang.Object
implements java.nio.channels.Channel, java.io.Flushable
```
Reads and writes individual pages in a database file

Field Summary

Fields
Modifier and Type	Field and Description
`private boolean`	`_autoSync` whether or not to force all writes to disk immediately
`private java.nio.channels.FileChannel`	`_channel` Channel containing the database
`private boolean`	`_closeChannel` whether or not the _channel should be closed by this class
`private CodecHandler`	`_codecHandler` handler for the current database encoding type
`private java.nio.ByteBuffer`	`_forceBytes` dummy buffer used when allocating new pages
`private JetFormat`	`_format` Format of the database in the channel
`private TempPageHolder`	`_fullPageEncodeBufferH` temp page buffer used when pages cannot be partially encoded
`private UsageMap`	`_globalUsageMap` Tracks free pages in the database.
`private java.nio.ByteBuffer`	`_invalidPageBytes` buffer used when deallocating old pages.
`private TempBufferHolder`	`_tempDecodeBufferH`
`private int`	`_writeCount`
`(package private) static java.nio.ByteOrder`	`DEFAULT_BYTE_ORDER`
`private static byte[]`	`INVALID_PAGE_BYTE_HEADER` invalid page header, used when deallocating old pages.
`(package private) static int`	`INVALID_PAGE_NUMBER`
`(package private) static int`	`PAGE_GLOBAL_USAGE_MAP` Global usage map always lives on page 1
`(package private) static int`	`ROW_GLOBAL_USAGE_MAP` Global usage map always lives at row 0

Constructor Summary

Constructors
Modifier	Constructor and Description
`protected`	`PageChannel(boolean testing)` Only used by unit tests
	`PageChannel(java.nio.channels.FileChannel channel, boolean closeChannel, JetFormat format, boolean autoSync)`

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`int`	`allocateNewPage()` Allocates a new page in the database.
`private void`	`applyHeaderMask(java.nio.ByteBuffer buffer)` Applies the XOR mask to the database header in the given buffer.
`private void`	`assertWriting()` Asserts that a write operation is in progress.
`void`	`close()`
`static java.nio.ByteBuffer`	`createBuffer(int size)`
`static java.nio.ByteBuffer`	`createBuffer(int size, java.nio.ByteOrder order)`
`java.nio.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()`
`private int`	`getNextPageNumber(long size)` Returns the next page number based on the given file size.
`private long`	`getPageOffset(int pageNumber)` Returns the offset for a page within the file.
`void`	`initialize(DatabaseImpl database, CodecProvider codecProvider)` Does second-stage initialization, must be called after construction.
`boolean`	`isAutoSync()`
`boolean`	`isOpen()`
`boolean`	`isWriting()` Returns `true` if a logical write operation is in progress, `false` otherwise.
`static java.nio.ByteBuffer`	`narrowBuffer(java.nio.ByteBuffer buffer, int position, int limit)`
`void`	`readPage(java.nio.ByteBuffer buffer, int pageNumber)`
`void`	`startWrite()` Begins a "logical" write operation.
`private void`	`validatePageNumber(int pageNumber)` Validates that the given pageNumber is valid for this database.
`static java.nio.ByteBuffer`	`wrap(byte[] bytes)` Returns a ByteBuffer wrapping the given bytes and configured with the default byte order.
`void`	`writePage(java.nio.ByteBuffer page, int pageNumber)` Write a page to disk
`void`	`writePage(java.nio.ByteBuffer page, int pageNumber, int pageOffset)` Write a page (or part of a page) to disk

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - INVALID_PAGE_NUMBER
```
static final int INVALID_PAGE_NUMBER
```
    See Also:
    
    Constant Field Values
  - DEFAULT_BYTE_ORDER
```
static final java.nio.ByteOrder DEFAULT_BYTE_ORDER
```
  - INVALID_PAGE_BYTE_HEADER
```
private static final byte[] INVALID_PAGE_BYTE_HEADER
```
    invalid page header, used when deallocating old pages. data pages generally have 4 interesting bytes at the beginning which we want to reset.
  - PAGE_GLOBAL_USAGE_MAP
```
static final int PAGE_GLOBAL_USAGE_MAP
```
    Global usage map always lives on page 1
    
    See Also:
    
    Constant Field Values
  - ROW_GLOBAL_USAGE_MAP
```
static final int ROW_GLOBAL_USAGE_MAP
```
    Global usage map always lives at row 0
    
    See Also:
    
    Constant Field Values
  - _channel
```
private final java.nio.channels.FileChannel _channel
```
    Channel containing the database
  - _closeChannel
```
private final boolean _closeChannel
```
    whether or not the _channel should be closed by this class
  - _format
```
private final JetFormat _format
```
    Format of the database in the channel
  - _autoSync
```
private final boolean _autoSync
```
    whether or not to force all writes to disk immediately
  - _invalidPageBytes
```
private final java.nio.ByteBuffer _invalidPageBytes
```
    buffer used when deallocating old pages. data pages generally have 4 interesting bytes at the beginning which we want to reset.
  - _forceBytes
```
private final java.nio.ByteBuffer _forceBytes
```
    dummy buffer used when allocating new pages
  - _globalUsageMap
```
private UsageMap _globalUsageMap
```
    Tracks free pages in the database.
  - _codecHandler
```
private CodecHandler _codecHandler
```
    handler for the current database encoding type
  - _fullPageEncodeBufferH
```
private TempPageHolder _fullPageEncodeBufferH
```
    temp page buffer used when pages cannot be partially encoded
  - _tempDecodeBufferH
```
private TempBufferHolder _tempDecodeBufferH
```
  - _writeCount
```
private int _writeCount
```
- Constructor Detail
  - PageChannel
```
protected PageChannel(boolean testing)
```
    Only used by unit tests
  - PageChannel
```
public PageChannel(java.nio.channels.FileChannel channel,
                   boolean closeChannel,
                   JetFormat format,
                   boolean autoSync)
            throws java.io.IOException
```
    Parameters:
    
    channel - Channel containing the database
    
    format - Format of the database in the channel
    
    Throws:
    
    java.io.IOException
- Method Detail
  - initialize
```
public void initialize(DatabaseImpl database,
                       CodecProvider codecProvider)
                throws java.io.IOException
```
    Does second-stage initialization, must be called after construction.
    
    Throws:
    
    java.io.IOException
  - getFormat
```
public JetFormat getFormat()
```
  - isAutoSync
```
public boolean isAutoSync()
```
  - startWrite
```
public void startWrite()
```
    Begins a "logical" write operation. See finishWrite() for more details.
  - finishWrite
```
public void finishWrite()
                 throws java.io.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:
    
    java.io.IOException
  - isWriting
```
public boolean isWriting()
```
    Returns true if a logical write operation is in progress, false otherwise.
  - assertWriting
```
private void assertWriting()
```
    Asserts that a write operation is in progress.
  - getNextPageNumber
```
private int getNextPageNumber(long size)
```
    Returns the next page number based on the given file size.
  - getPageOffset
```
private long getPageOffset(int pageNumber)
```
    Returns the offset for a page within the file.
  - validatePageNumber
```
private void validatePageNumber(int pageNumber)
                         throws java.io.IOException
```
    Validates that the given pageNumber is valid for this database.
    
    Throws:
    
    java.io.IOException
  - readPage
```
public void readPage(java.nio.ByteBuffer buffer,
                     int pageNumber)
              throws java.io.IOException
```
    Parameters:
    
    buffer - Buffer to read the page into
    
    pageNumber - Number of the page to read in (starting at 0)
    
    Throws:
    
    java.io.IOException
  - writePage
```
public void writePage(java.nio.ByteBuffer page,
                      int pageNumber)
               throws java.io.IOException
```
    Write a page to disk
    
    Parameters:
    
    page - Page to write
    
    pageNumber - Page number to write the page to
    
    Throws:
    
    java.io.IOException
  - writePage
```
public void writePage(java.nio.ByteBuffer page,
                      int pageNumber,
                      int pageOffset)
               throws java.io.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:
    
    java.io.IOException
  - allocateNewPage
```
public int allocateNewPage()
                    throws java.io.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:
    
    java.io.IOException
  - deallocatePage
```
public void deallocatePage(int pageNumber)
                    throws java.io.IOException
```
    Deallocate a previously used page in the database.
    
    Throws:
    
    java.io.IOException
  - createPageBuffer
```
public java.nio.ByteBuffer createPageBuffer()
```
    Returns:
    
    A newly-allocated buffer that can be passed to readPage
  - createBuffer
```
public static java.nio.ByteBuffer createBuffer(int size)
```
    Returns:
    
    A newly-allocated buffer of the given size and DEFAULT_BYTE_ORDER byte order
  - createBuffer
```
public static java.nio.ByteBuffer createBuffer(int size,
                                               java.nio.ByteOrder order)
```
    Returns:
    
    A newly-allocated buffer of the given size and byte order
  - flush
```
public void flush()
           throws java.io.IOException
```
    Specified by:
    
    flush in interface java.io.Flushable
    
    Throws:
    
    java.io.IOException
  - close
```
public void close()
           throws java.io.IOException
```
    Specified by:
    
    close in interface java.io.Closeable
    
    Specified by:
    
    close in interface java.lang.AutoCloseable
    
    Specified by:
    
    close in interface java.nio.channels.Channel
    
    Throws:
    
    java.io.IOException
  - isOpen
```
public boolean isOpen()
```
    Specified by:
    
    isOpen in interface java.nio.channels.Channel
  - applyHeaderMask
```
private void applyHeaderMask(java.nio.ByteBuffer buffer)
```
    Applies the XOR mask to the database header in the given buffer.
  - narrowBuffer
```
public static java.nio.ByteBuffer narrowBuffer(java.nio.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 java.nio.ByteBuffer wrap(byte[] bytes)
```
    Returns a ByteBuffer wrapping the given bytes and configured with the default byte order.

Class PageChannel

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

INVALID_PAGE_NUMBER

DEFAULT_BYTE_ORDER

INVALID_PAGE_BYTE_HEADER

PAGE_GLOBAL_USAGE_MAP

ROW_GLOBAL_USAGE_MAP

_channel

_closeChannel

_format

_autoSync

_invalidPageBytes

_forceBytes

_globalUsageMap

_codecHandler

_fullPageEncodeBufferH

_tempDecodeBufferH

_writeCount

Constructor Detail

PageChannel

PageChannel

Method Detail

initialize

getFormat

isAutoSync

startWrite

finishWrite

isWriting

assertWriting

getNextPageNumber

getPageOffset

validatePageNumber

readPage

writePage

writePage

allocateNewPage

deallocatePage

createPageBuffer

createBuffer

createBuffer

flush

close

isOpen

applyHeaderMask

narrowBuffer

wrap