| java.lang.Object
 net.sourceforge.jtds.util.BlobBuffer
| BlobBuffer | | public class BlobBuffer (Code) | | 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.
author:
Mike Hutchinson
version:
$Id: BlobBuffer.java,v 1.4 2007/07/08 21:38:14 bheineman Exp $ |
| Constructor Summary | |
| public | BlobBuffer(File bufferDir, long maxMemSize)
Creates a blob buffer. |
| Method Summary | |
| public void | close()
Logically closes the file or physically close it if the open count is
now zero. | | public void | createBlobFile()
Creates a random access disk file to use as backing storage for the LOB
data. | | protected void | finalize()
Finalizes this object by deleting any work files. | | public InputStream | getBinaryStream(boolean ascii)
Retrieve the BLOB data as an InputStream. | | public byte[] | getBytes(long pos, int len)
Returns the BLOB data as a byte array. | | public long | getLength()
Retrieves the length of this BLOB buffer in bytes. | | public InputStream | getUnicodeStream()
Retrieve the BLOB data as an Big Endian Unicode
InputStream. | | public void | growBuffer(int minSize)
Increases the size of the in memory buffer for situations where disk
storage of BLOB is not possible. | | public void | open()
Opens the BLOB disk file. | | public int | position(byte[] pattern, long start)
Provides support for pattern searching methods. | | public int | read(int readPtr)
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. | | public int | read(int readPtr, byte[] bytes, int offset, int len)
Reads bytes from the BLOB buffer at the specified location. | | public void | readPage(int page)
Reads in the specified page from the disk buffer. | | public OutputStream | setBinaryStream(long pos, boolean ascii)
Creates an OutputStream that can be used to update the
BLOB. | | public void | setBuffer(byte[] bytes, boolean copy)
Sets the initial buffer to an existing byte array. | | public int | setBytes(long pos, byte[] bytes, int offset, int len, boolean copy)
Sets the content of the BLOB to the supplied byte array value. | | public void | setLength(long length)
Retrieves the length of the BLOB buffer (in memory version only). | | public void | truncate(long len)
Truncates the BLOB buffer to the specified size. | | public void | write(int writePtr, int b)
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. | | void | write(int writePtr, byte[] bytes, int offset, int len)
Inserts bytes into the buffer at the specified location. | | public void | writePage(int page)
Writes the specified page to the disk buffer. |
| BlobBuffer | | public BlobBuffer(File bufferDir, long maxMemSize)(Code) | | Creates a blob buffer.
Parameters:
bufferDir -
Parameters:
maxMemSize - the maximum size of the in memory buffer |
| close | | public void close() throws IOException(Code) | | 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.
throws:
IOException - if an I/O error occurs |
| createBlobFile | | public void createBlobFile()(Code) | | 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(Code) | | Finalizes this object by deleting any work files.
|
| getBinaryStream | | public InputStream getBinaryStream(boolean ascii) throws SQLException(Code) | | Retrieve the BLOB data as an InputStream.
Parameters:
ascii - true if an ASCII input stream should be returned the InputStream built over the BLOB data
throws:
SQLException - if an error occurs |
| getBytes | | public byte[] getBytes(long pos, int len) throws SQLException(Code) | | Returns the BLOB data as a byte array.
Parameters:
pos - the start position in the BLOB buffer (from 1)
Parameters:
len - the number of bytes to copy the requested data as a byte[] |
| getLength | | public long getLength()(Code) | | Retrieves the length of this BLOB buffer in bytes.
the length of the BLOB data in bytes |
| getUnicodeStream | | public InputStream getUnicodeStream() throws SQLException(Code) | | Retrieve the BLOB data as an Big Endian Unicode
InputStream.
the InputStream built over the BLOB data
throws:
SQLException - if an error occurs |
| growBuffer | | public void growBuffer(int minSize)(Code) | | Increases the size of the in memory buffer for situations where disk
storage of BLOB is not possible.
Parameters:
minSize - the minimum size of buffer required |
| open | | public void open() throws IOException(Code) | | 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.
throws:
IOException - if an I/O error occurs |
| position | | public int position(byte[] pattern, long start) throws SQLException(Code) | | Provides support for pattern searching methods.
Parameters:
pattern - the byte array containg the search pattern
Parameters:
start - the start position in the BLOB (from 1) the int start index for the pattern (from 1) or -1if the pattern is not found.
throws:
SQLException - if an error occurs |
| read | | public int read(int readPtr) throws IOException(Code) | | 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.
Parameters:
readPtr - the offset in the buffer of the required byte the byte value as an int or -1 if at EOF
throws:
IOException - if an I/O error occurs |
| read | | public int read(int readPtr, byte[] bytes, int offset, int len) throws IOException(Code) | | Reads bytes from the BLOB buffer at the specified location.
Parameters:
readPtr - the offset in the buffer of the required byte
Parameters:
bytes - the byte array to fill
Parameters:
offset - the start position in the byte array
Parameters:
len - the number of bytes to read the number of bytes read or -1 if at end of file
throws:
IOException - if an I/O error occurs |
| readPage | | public void readPage(int page) throws IOException(Code) | | Reads in the specified page from the disk buffer.
Any existing dirty page is first saved to disk.
Parameters:
page - the page number
throws:
IOException - if an I/O error occurs |
| setBinaryStream | | public OutputStream setBinaryStream(long pos, boolean ascii) throws SQLException(Code) | | 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.
Parameters:
pos - the start position in the buffer (from 1)
Parameters:
ascii - true if an ASCII output stream is required the OutputStream to be used to update the BLOB
throws:
SQLException - if an error occurs |
| setBuffer | | public void setBuffer(byte[] bytes, boolean copy)(Code) | | Sets the initial buffer to an existing byte array.
Parameters:
bytes - the byte array containing the BLOB data
Parameters:
copy - 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(Code) | | 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.
Parameters:
pos - the start position in the buffer (from 1)
Parameters:
bytes - the byte array containing the data to copy
Parameters:
offset - the start position in the byte array (from 0)
Parameters:
len - the number of bytes to copy
Parameters:
copy - true if a local copy of the byte array is required the number of bytes copied
throws:
SQLException - if an error occurs |
| setLength | | public void setLength(long length)(Code) | | Retrieves the length of the BLOB buffer (in memory version only).
Parameters:
length - the length of the valid data in the buffer |
| truncate | | public void truncate(long len) throws SQLException(Code) | | Truncates the BLOB buffer to the specified size.
Parameters:
len - the required length
throws:
SQLException - if an error occurs |
| write | | public void write(int writePtr, int b) throws IOException(Code) | | 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.
Parameters:
writePtr - the offset in the buffer of the required byte
Parameters:
b - the byte value to write
throws:
IOException - if an I/O error occurs |
| write | | void write(int writePtr, byte[] bytes, int offset, int len) throws IOException(Code) | | Inserts bytes into the buffer at the specified location.
Parameters:
writePtr - the offset in the buffer of the required byte
Parameters:
bytes - the byte array value to write
Parameters:
offset - the start position in the byte array
Parameters:
len - the number of bytes to write
throws:
IOException - if an I/O error occurs |
| writePage | | public void writePage(int page) throws IOException(Code) | | Writes the specified page to the disk buffer.
Parameters:
page - the page number
throws:
IOException - if an I/O error occurs |
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