Package net.sourceforge.jtds.util

Class BlobBuffer

  • public class BlobBuffer
extends java.lang.Object
    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:

    1. 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.
    2. 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.
    3. 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.
    4. 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.
    Version:
    $Id: BlobBuffer.java,v 1.4.2.1 2009-08-03 12:31:00 ickzon Exp $
    Author:
    Mike Hutchinson

    • Field Summary

      Fields 
      Modifier and Type Field Description
      private java.io.File blobFile
      The name of the temporary BLOB disk file.
      private byte[] buffer
      The BLOB buffer or the current page buffer.
      private java.io.File bufferDir
      The directory to buffer data to.
      private boolean bufferDirty
      Indicates page in memory must be saved.
      private static int BYTE_MASK
      Mask for page offset component of R/W pointer.
      private int currentPage
      The number of the current page in memory.
      private static byte[] EMPTY_BUFFER
      Default zero length buffer.
      private static int INVALID_PAGE
      Invalid page marker.
      private boolean isMemOnly
      True if attempts to create a BLOB file have failed or the buffer is created without specifying a buffer directory.
      private int length
      The total length of the valid data in buffer.
      private static int MAX_BUF_INC
      Maximum buffer increment.
      private int maxMemSize
      The maximum size of an in memory buffer.
      private int openCount
      Count of callers that have opened the BLOB file.
      private static int PAGE_MASK
      Mask for page component of read/write pointer.
      private static int PAGE_SIZE
      Default page size (must be power of 2).
      private java.io.RandomAccessFile raFile
      The RA file object reference or null if closed.

    • Constructor Summary

      Constructors 
      Constructor Description
      BlobBuffer​(java.io.File bufferDir, long maxMemSize)
      Creates a blob buffer.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void close()
      Logically closes the file or physically close it if the open count is now zero.
      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.
      java.io.InputStream getBinaryStream​(boolean ascii)
      Retrieve the BLOB data as an InputStream.
      byte[] getBytes​(long pos, int len)
      Returns the BLOB data as a byte array.
      long getLength()
      Retrieves the length of this BLOB buffer in bytes.
      java.io.InputStream getUnicodeStream()
      Retrieve the BLOB data as an Big Endian Unicode InputStream.
      void growBuffer​(int minSize)
      Increases the size of the in memory buffer for situations where disk storage of BLOB is not possible.
      void open()
      Opens the BLOB disk file.
      int position​(byte[] pattern, long start)
      Provides support for pattern searching methods.
      int read​(int readPtr)
      Reads byte from the BLOB buffer at the specified location.
      int read​(int readPtr, byte[] bytes, int offset, int len)
      Reads bytes from the BLOB buffer at the specified location.
      void readPage​(int page)
      Reads in the specified page from the disk buffer.
      java.io.OutputStream setBinaryStream​(long pos, boolean ascii)
      Creates an OutputStream that can be used to update the BLOB.
      void setBuffer​(byte[] bytes, boolean copy)
      Sets the initial buffer to an existing byte array.
      int setBytes​(long pos, byte[] bytes, int offset, int len, boolean copy)
      Sets the content of the BLOB to the supplied byte array value.
      void setLength​(long length)
      Retrieves the length of the BLOB buffer (in memory version only).
      void truncate​(long len)
      Truncates the BLOB buffer to the specified size.
      (package private) void write​(int writePtr, byte[] bytes, int offset, int len)
      Inserts bytes into the buffer at the specified location.
      void write​(int writePtr, int b)
      Inserts a byte into the buffer at the specified location.
      void writePage​(int page)
      Writes the specified page to the disk buffer.

      • Methods inherited from class java.lang.Object

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

    • Field Detail

      • EMPTY_BUFFER

        private static final byte[] EMPTY_BUFFER
        Default zero length buffer.

      • PAGE_SIZE

        private static final int PAGE_SIZE
        Default page size (must be power of 2).
        See Also:
        Constant Field Values

      • PAGE_MASK

        private static final int PAGE_MASK
        Mask for page component of read/write pointer.
        See Also:
        Constant Field Values

      • BYTE_MASK

        private static final int BYTE_MASK
        Mask for page offset component of R/W pointer.
        See Also:
        Constant Field Values

      • MAX_BUF_INC

        private static final int MAX_BUF_INC
        Maximum buffer increment.
        See Also:
        Constant Field Values

      • INVALID_PAGE

        private static final int INVALID_PAGE
        Invalid page marker.
        See Also:
        Constant Field Values

      • buffer

        private byte[] buffer
        The BLOB buffer or the current page buffer.

      • length

        private int length
        The total length of the valid data in buffer.

      • currentPage

        private int currentPage
        The number of the current page in memory.

      • blobFile

        private java.io.File blobFile
        The name of the temporary BLOB disk file.

      • raFile

        private java.io.RandomAccessFile raFile
        The RA file object reference or null if closed.

      • bufferDirty

        private boolean bufferDirty
        Indicates page in memory must be saved.

      • openCount

        private int openCount
        Count of callers that have opened the BLOB file.

      • isMemOnly

        private boolean isMemOnly
        True if attempts to create a BLOB file have failed or the buffer is created without specifying a buffer directory.

      • bufferDir

        private final java.io.File bufferDir
        The directory to buffer data to.

      • maxMemSize

        private final int maxMemSize
        The maximum size of an in memory buffer.

    • Constructor Detail

      • BlobBuffer

        public BlobBuffer​(java.io.File bufferDir,
                  long maxMemSize)
        Creates a blob buffer.
        Parameters:
        bufferDir -
        maxMemSize - the maximum size of the in memory buffer

    • Method Detail

      • finalize

        protected void finalize()
                 throws java.lang.Throwable
        Finalizes this object by deleting any work files.
        Overrides:
        finalize in class java.lang.Object
        Throws:
        java.lang.Throwable

      • 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.

      • open

        public void open()
          throws java.io.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.

        Throws:
        java.io.IOException - if an I/O error occurs

      • read

        public int read​(int readPtr)
         throws java.io.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.

        Parameters:
        readPtr - the offset in the buffer of the required byte
        Returns:
        the byte value as an int or -1 if at EOF
        Throws:
        java.io.IOException - if an I/O error occurs

      • read

        public int read​(int readPtr,
                byte[] bytes,
                int offset,
                int len)
         throws java.io.IOException
        Reads bytes from the BLOB buffer at the specified location.
        Parameters:
        readPtr - the offset in the buffer of the required byte
        bytes - the byte array to fill
        offset - the start position in the byte array
        len - the number of bytes to read
        Returns:
        the number of bytes read or -1 if at end of file
        Throws:
        java.io.IOException - if an I/O error occurs

      • write

        public void write​(int writePtr,
                  int b)
           throws java.io.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.

        Parameters:
        writePtr - the offset in the buffer of the required byte
        b - the byte value to write
        Throws:
        java.io.IOException - if an I/O error occurs

      • write

        void write​(int writePtr,
           byte[] bytes,
           int offset,
           int len)
    throws java.io.IOException
        Inserts bytes into the buffer at the specified location.
        Parameters:
        writePtr - the offset in the buffer of the required byte
        bytes - the byte array value to write
        offset - the start position in the byte array
        len - the number of bytes to write
        Throws:
        java.io.IOException - if an I/O error occurs

      • readPage

        public void readPage​(int page)
              throws java.io.IOException
        Reads in the specified page from the disk buffer.

        Any existing dirty page is first saved to disk.

        Parameters:
        page - the page number
        Throws:
        java.io.IOException - if an I/O error occurs

      • writePage

        public void writePage​(int page)
               throws java.io.IOException
        Writes the specified page to the disk buffer.
        Parameters:
        page - the page number
        Throws:
        java.io.IOException - if an I/O error occurs

      • close

        public void close()
           throws java.io.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.

        Throws:
        java.io.IOException - if an I/O error occurs

      • growBuffer

        public void growBuffer​(int minSize)
        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

      • setBuffer

        public void setBuffer​(byte[] bytes,
                      boolean copy)
        Sets the initial buffer to an existing byte array.
        Parameters:
        bytes - the byte array containing the BLOB data
        copy - true if a local copy of the data is required

      • getBytes

        public byte[] getBytes​(long pos,
                       int len)
                throws java.sql.SQLException
        Returns the BLOB data as a byte array.
        Parameters:
        pos - the start position in the BLOB buffer (from 1)
        len - the number of bytes to copy
        Returns:
        the requested data as a byte[]
        Throws:
        java.sql.SQLException

      • getBinaryStream

        public java.io.InputStream getBinaryStream​(boolean ascii)
                                    throws java.sql.SQLException
        Retrieve the BLOB data as an InputStream.
        Parameters:
        ascii - true if an ASCII input stream should be returned
        Returns:
        the InputStream built over the BLOB data
        Throws:
        java.sql.SQLException - if an error occurs

      • getUnicodeStream

        public java.io.InputStream getUnicodeStream()
                                     throws java.sql.SQLException
        Retrieve the BLOB data as an Big Endian Unicode InputStream.
        Returns:
        the InputStream built over the BLOB data
        Throws:
        java.sql.SQLException - if an error occurs

      • setBinaryStream

        public java.io.OutputStream setBinaryStream​(long pos,
                                            boolean ascii)
                                     throws java.sql.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.

        Parameters:
        pos - the start position in the buffer (from 1)
        ascii - true if an ASCII output stream is required
        Returns:
        the OutputStream to be used to update the BLOB
        Throws:
        java.sql.SQLException - if an error occurs

      • setBytes

        public int setBytes​(long pos,
                    byte[] bytes,
                    int offset,
                    int len,
                    boolean copy)
             throws java.sql.SQLException
        Sets the content of the BLOB to the supplied byte array value.

        If the following conditions are met:

        1. The start position is 1
        2. The existing BLOB length is smaller or the same as the length of the new data
        3. 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)
        bytes - the byte array containing the data to copy
        offset - the start position in the byte array (from 0)
        len - the number of bytes to copy
        copy - true if a local copy of the byte array is required
        Returns:
        the number of bytes copied
        Throws:
        java.sql.SQLException - if an error occurs

      • getLength

        public long getLength()
        Retrieves the length of this BLOB buffer in bytes.
        Returns:
        the length of the BLOB data in bytes

      • setLength

        public void setLength​(long length)
        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 java.sql.SQLException
        Truncates the BLOB buffer to the specified size.
        Parameters:
        len - the required length
        Throws:
        java.sql.SQLException - if an error occurs

      • position

        public int position​(byte[] pattern,
                    long start)
             throws java.sql.SQLException
        Provides support for pattern searching methods.
        Parameters:
        pattern - the byte array containg the search pattern
        start - the start position in the BLOB (from 1)
        Returns:
        the int start index for the pattern (from 1) or -1 if the pattern is not found.
        Throws:
        java.sql.SQLException - if an error occurs