Manages a buffer (backed by optional disk storage) for use as a data store
by the CLOB and BLOB objects.
The data can be purely memory based until the size exceeds the value
dictated by the
lobBuffer
URL property after which it will be
written to disk. The disk array is accessed randomly one page (1024 bytes)
at a time.
This class is not synchronized and concurrent open input and output
streams can conflict.
Tuning hints:
- The
PAGE_SIZE
governs how much data is buffered when
reading or writing data a byte at a time. 1024 bytes seems to work well
but if very large objects are being written a byte at a time 4096 may be
better. NB. ensure that the PAGE_MASK
and
BYTE_MASK
fields are also adjusted to match.
- Reading or writing byte arrays that are greater than or equal to the
page size will go directly to or from the random access file cutting out
an ArrayCopy operation.
- If BLOBs are being buffered exclusively in memory you may wish to
adjust the
MAX_BUF_INC
value. Every time the buffer is
expanded the existing contents are copied and this may get expensive
with very large BLOBs.
- The BLOB file will be kept open for as long as there are open input or
output streams. Therefore BLOB streams should be explicitly closed as
soon as they are finished with.
BYTE_MASK
private static final int BYTE_MASK
Mask for page offset component of R/W pointer.
EMPTY_BUFFER
private static final byte[] EMPTY_BUFFER
Default zero length buffer.
INVALID_PAGE
private static final int INVALID_PAGE
Invalid page marker.
MAX_BUF_INC
private static final int MAX_BUF_INC
Maximum buffer increment.
PAGE_MASK
private static final int PAGE_MASK
Mask for page component of read/write pointer.
PAGE_SIZE
private static final int PAGE_SIZE
Default page size (must be power of 2).
blobFile
private File blobFile
The name of the temporary BLOB disk file.
buffer
private byte[] buffer
The BLOB buffer or the current page buffer.
bufferDir
private final File bufferDir
The directory to buffer data to.
bufferDirty
private boolean bufferDirty
Indicates page in memory must be saved.
currentPage
private int currentPage
The number of the current page in memory.
isMemOnly
private boolean isMemOnly
True if attempts to create a BLOB file have failed.
length
private int length
The total length of the valid data in buffer.
maxMemSize
private final int maxMemSize
The maximum size of an in memory buffer.
openCount
private int openCount
Count of callers that have opened the BLOB file.
raFile
private RandomAccessFile raFile
The RA file object reference or null if closed.
close
public void close()
throws IOException
Logically closes the file or physically close it if the open count is
now zero.
Any updated buffer in memory is flushed to disk before the file is
closed.
createBlobFile
public void createBlobFile()
Creates a random access disk file to use as backing storage for the LOB
data.
This method may fail due to security exceptions or local disk problems,
in which case the blob storage will remain entirely in memory.
finalize
protected void finalize()
throws Throwable
Finalizes this object by deleting any work files.
getBinaryStream
public InputStream getBinaryStream(boolean ascii)
throws SQLException
Retrieve the BLOB data as an InputStream
.
ascii
- true if an ASCII input stream should be returned
- the
InputStream
built over the BLOB data
getBytes
public byte[] getBytes(long pos,
int len)
throws SQLException
Returns the BLOB data as a byte array.
pos
- the start position in the BLOB buffer (from 1)len
- the number of bytes to copy
- the requested data as a
byte[]
getLength
public long getLength()
Retrieves the length of this BLOB buffer in bytes.
- the length of the BLOB data in bytes
getUnicodeStream
public InputStream getUnicodeStream()
throws SQLException
Retrieve the BLOB data as an Big Endian Unicode
InputStream
.
- the
InputStream
built over the BLOB data
growBuffer
public void growBuffer(int minSize)
Increases the size of the in memory buffer for situations where disk
storage of BLOB is not possible.
minSize
- the minimum size of buffer required
open
public void open()
throws IOException
Opens the BLOB disk file.
A count of open and close requests is kept so that the file may be
closed when no longer required thus keeping the number of open files to
a minimum.
position
public int position(byte[] pattern,
long start)
throws SQLException
Provides support for pattern searching methods.
pattern
- the byte array containg the search patternstart
- the start position in the BLOB (from 1)
- the
int
start index for the pattern (from 1) or -1
if the pattern is not found.
read
public int read(int readPtr)
throws IOException
Reads byte from the BLOB buffer at the specified location.
The read pointer is partitioned into a page number and an offset within
the page. This routine will read new pages as required. The page size
must be a power of 2 and is currently set to 1024 bytes.
readPtr
- the offset in the buffer of the required byte
- the byte value as an
int
or -1 if at EOF
read
public int read(int readPtr,
byte[] bytes,
int offset,
int len)
throws IOException
Reads bytes from the BLOB buffer at the specified location.
readPtr
- the offset in the buffer of the required bytebytes
- the byte array to filloffset
- the start position in the byte arraylen
- the number of bytes to read
- the number of bytes read or -1 if at end of file
readPage
public void readPage(int page)
throws IOException
Reads in the specified page from the disk buffer.
Any existing dirty page is first saved to disk.
setBinaryStream
public OutputStream setBinaryStream(long pos,
boolean ascii)
throws SQLException
Creates an
OutputStream
that can be used to update the
BLOB.
Given that we cannot know the final size of a BLOB created by the caller
of this method, we assume the worst and create a disk BLOB by default.
pos
- the start position in the buffer (from 1)ascii
- true if an ASCII output stream is required
- the
OutputStream
to be used to update the BLOB
setBuffer
public void setBuffer(byte[] bytes,
boolean copy)
Sets the initial buffer to an existing byte array.
bytes
- the byte array containing the BLOB datacopy
- true if a local copy of the data is required
setBytes
public int setBytes(long pos,
byte[] bytes,
int offset,
int len,
boolean copy)
throws SQLException
Sets the content of the BLOB to the supplied byte array value.
If the following conditions are met:
- The start position is 1
- The existing BLOB length is smaller or the same as the length of
the new data
- The new data length does not exceed the in memory limit
then the new data is buffered entirely in memory, otherwise a disk file
is created.
pos
- the start position in the buffer (from 1)bytes
- the byte array containing the data to copyoffset
- the start position in the byte array (from 0)len
- the number of bytes to copycopy
- true if a local copy of the byte array is required
- the number of bytes copied
setLength
public void setLength(long length)
Retrieves the length of the BLOB buffer (in memory version only).
length
- the length of the valid data in the buffer
truncate
public void truncate(long len)
throws SQLException
Truncates the BLOB buffer to the specified size.
len
- the required length
write
(package private) void write(int writePtr,
byte[] bytes,
int offset,
int len)
throws IOException
Inserts bytes into the buffer at the specified location.
writePtr
- the offset in the buffer of the required bytebytes
- the byte array value to writeoffset
- the start position in the byte arraylen
- the number of bytes to write
write
public void write(int writePtr,
int b)
throws IOException
Inserts a byte into the buffer at the specified location.
The write pointer is partitioned into a page number and an offset within
the page. This routine will write new pages as required. The page size
must be a power of 2 and is currently set to 1024 bytes.
writePtr
- the offset in the buffer of the required byteb
- the byte value to write
writePage
public void writePage(int page)
throws IOException
Writes the specified page to the disk buffer.