Class EmbedBlob

java.lang.Object
org.apache.derby.impl.jdbc.ConnectionChild
org.apache.derby.impl.jdbc.EmbedBlob
All Implemented Interfaces:
Blob, EngineLOB
final class EmbedBlob extends ConnectionChild implements Blob, EngineLOB
Implements java.sql.Blob (see the JDBC 2.0 spec). A blob sits on top of a BINARY, VARBINARY or LONG VARBINARY column. If its data is small (less than 1 page) it is a byte array taken from the SQLBit class. If it is large (more than 1 page) it is a long column in the database. The long column is accessed as a stream, and is implemented in store as an OverflowInputStream. The Resetable interface allows sending messages to that stream to initialize itself (reopen its container and lock the corresponding row) and to reset itself to the beginning. NOTE: In the case that the data is large, it is represented as a stream. This stream is returned to the user in the getBinaryStream() method. This means that we have limited control over the state of the stream, since the user can read bytes from it at any time. Thus all methods here reset the stream to the beginning before doing any work. CAVEAT: The methods may not behave correctly if a user sets up multiple threads and sucks data from the stream (returned from getBinaryStream()) at the same time as calling the Blob methods.

Supports

  • JSR169 - no subsetting for java.sql.Blob
  • JDBC 2.0
  • JDBC 3.0 - no new dependencies on new JDBC 3.0 or JDK 1.4 classes, new update methods can safely be added into implementation.

  • Field Details

    • materialized

      private boolean materialized
      Tells whether the Blob has been materialized or not.

      Materialization happens when the Blob is updated by the user. A materialized Blob is represented either in memory or in a temporary file on disk, depending on size.

      A Blob that has not been materialized is represented by a stream into the Derby store, and is read-only.

    • myStream

      private PositionedStoreStream myStream
      The underlying positionable store stream, if any.

      If materialized is true, the stream is null.

    • locator

      private int locator
      Locator value for this Blob, used as a handle by the client driver to map operations to the correct Blob on the server side.
      See Also:

    • streamLength

      private long streamLength
      Length of the stream representing the Blob.

      Set to -1 when the stream has been materialized or the length of the stream is not currently known.

    • streamPositionOffset

      private final int streamPositionOffset
      Position offset for the stream representing the Blob, if any.

      This offset accounts for the bytes encoding the stream length at the head of the stream. Data byte pos is at pos + streamPositionOffset in the underlying stream. Set to Integer.MIN_VALUE if the Blob isn't represented by a store stream.

    • isValid

      private boolean isValid

    • control

      private LOBStreamControl control

  • Constructor Details

  • Method Details

    • handleStreamValue

      private int handleStreamValue(InputStream dvdStream, EmbedConnection con) throws StandardException, SQLException
      Constructs a Blob object on top of a stream.
      Parameters:
      dvdStream - the source stream
      con - the connection owning the Blob
      Returns:
      The offset into the stream where the user data begins (used if resetting the stream).
      Throws:
      StandardException - if accessing the stream fails, or if writing data to temporary storage fails
      SQLException

    • setBlobPosition

      private long setBlobPosition(long logicalPos) throws StandardException, IOException
      Sets the position of the Blob to logicalPos, where position 0 is the beginning of the Blob content.

      The position is only guaranteed to be valid from the time this method is invoked until the synchronization monitor is released, or until the next invokation of this method.

      The position is logical in the sense that it specifies the requested position in the Blob content. This position might be at a different position in the underlying representation, for instance the Derby store stream prepends the Blob content with a length field.

      Parameters:
      logicalPos - requested Blob position, 0-based
      Returns:
      The new position, which will be equal to the requested position.
      Throws:
      IOException - if reading/accessing the Blob fails
      StandardException - throws BLOB_POSITION_TOO_LARGE if the requested position is larger than the Blob length, throws other SQL states if resetting the stream fails

    • read

      private int read(long pos) throws IOException, StandardException
      Reads one byte from the Blob at the specified position.

      Depending on the representation, this might result in a read from a byte array, a temporary file on disk or from a Derby store stream.

      Returns:
      the byte at the current position, or -1 if end of file has been reached
      Throws:
      IOException - if reading from the underlying data representation fails
      StandardException

    • length

      public long length() throws SQLException
      Returns the number of bytes in the BLOB value designated by this Blob object.
      Specified by:
      length in interface Blob
      Returns:
      length of the BLOB in bytes
      Throws:
      SQLException - if there is an error accessing the length of the BLOB

    • getBytes

      public byte[] getBytes(long startPos, int length) throws SQLException
      Returns as an array of bytes part or all of the BLOB value that this Blob object designates. The byte array contains up to length consecutive bytes starting at position startPos. The starting position must be between 1 and the length of the BLOB plus 1. This allows for zero-length BLOB values, from which only zero-length byte arrays can be returned. If a larger length is requested than there are bytes available, characters from the start position to the end of the BLOB are returned.
      Specified by:
      getBytes in interface Blob
      Parameters:
      startPos - the ordinal position of the first byte in the BLOB value to be extracted; the first byte is at position 1
      length - is the number of consecutive bytes to be copied
      Returns:
      a byte array containing up to length consecutive bytes from the BLOB value designated by this Blob object, starting with the byte at position startPos.
      Throws:
      SQLException - if there is an error accessing the BLOB NOTE: If the starting position is the length of the BLOB plus 1, zero bytess are returned regardless of the length requested.

    • getBinaryStream

      public InputStream getBinaryStream() throws SQLException
      Retrieves the BLOB designated by this Blob instance as a stream.
      Specified by:
      getBinaryStream in interface Blob
      Returns:
      a stream containing the BLOB data
      Throws:
      SQLException - if there is an error accessing the BLOB

    • position

      public long position(byte[] pattern, long start) throws SQLException
      Determines the byte position at which the specified byte pattern begins within the BLOB value that this Blob object represents. The search for pattern. begins at position start
      Specified by:
      position in interface Blob
      Parameters:
      pattern - the byte array for which to search
      start - the position at which to begin searching; the first position is 1
      Returns:
      the position at which the pattern appears, else -1.
      Throws:
      SQLException - if there is an error accessing the BLOB

    • checkMatch

      private boolean checkMatch(byte[] pattern, long pos) throws IOException, StandardException
      Checks if the pattern (starting from the second byte) appears inside the Blob content.

      At this point, the first byte of the pattern must already have been matched, and pos must be pointing at the second byte to compare.

      Parameters:
      pattern - the byte array to search for, passed in by the user
      pos - the position in the Blob content to start searching from
      Returns:
      true if a match is found, false if not.
      Throws:
      IOException
      StandardException

    • position

      public long position(Blob pattern, long start) throws SQLException
      Determines the byte position in the BLOB value designated by this Blob object at which pattern begins. The search begins at position start.
      Specified by:
      position in interface Blob
      Parameters:
      pattern - the Blob object designating the BLOB value for which to search
      start - the position in the BLOB value at which to begin searching; the first position is 1
      Returns:
      the position at which the pattern begins, else -1
      Throws:
      SQLException - if there is an error accessing the BLOB

    • checkMatch

      private boolean checkMatch(Blob pattern, long pos) throws IOException, StandardException
      Checks if the pattern (starting from the second byte) appears inside the Blob content.
      Parameters:
      pattern - the Blob to search for, passed in by the user
      pos - the position in the Blob (this) content to start searching
      Returns:
      true if a match is found, false if not.
      Throws:
      IOException
      StandardException

    • handleMyExceptions

      private SQLException handleMyExceptions(Throwable t) throws SQLException
      Throws:
      SQLException

    • finalize

      protected void finalize()
      Overrides:
      finalize in class Object

    • setBytes

      public int setBytes(long pos, byte[] bytes) throws SQLException
      Writes the given array of bytes to the BLOB value that this Blob object represents, starting at position pos, and returns the number of bytes written.
      Specified by:
      setBytes in interface Blob
      Parameters:
      pos - the position in the BLOB object at which to start writing
      bytes - the array of bytes to be written to the BLOB value that this Blob object represents
      Returns:
      The number of bytes written to the BLOB.
      Throws:
      SQLException - if writing the bytes to the BLOB fails
      Since:
      1.4

    • setBytes

      public int setBytes(long pos, byte[] bytes, int offset, int len) throws SQLException
      Writes all or part of the given array of byte array to the BLOB value that this Blob object represents and returns the number of bytes written. Writing starts at position pos in the BLOB value; len bytes from the given byte array are written.
      Specified by:
      setBytes in interface Blob
      Parameters:
      pos - the position in the BLOB object at which to start writing
      bytes - the array of bytes to be written to the BLOB value that this Blob object represents
      offset - the offset into the byte array at which to start reading the bytes to be written
      len - the number of bytes to be written to the BLOB value from the array of bytes bytes
      Returns:
      The number of bytes written to the BLOB.
      Throws:
      SQLException - if writing the bytes to the BLOB fails
      IndexOutOfBoundsException - if len is larger than bytes.length - offset
      Since:
      1.4

    • setBinaryStream

      public OutputStream setBinaryStream(long pos) throws SQLException
      JDBC 3.0 Retrieves a stream that can be used to write to the BLOB value that this Blob object represents. The stream begins at position pos.
      Specified by:
      setBinaryStream in interface Blob
      Parameters:
      pos - - the position in the BLOB object at which to start writing
      Returns:
      a java.io.OutputStream object to which data can be written
      Throws:
      SQLException - Feature not implemented for now.

    • truncate

      public void truncate(long len) throws SQLException
      JDBC 3.0 Truncates the BLOB value that this Blob object represents to be len bytes in length.
      Specified by:
      truncate in interface Blob
      Parameters:
      len - - the length, in bytes, to which the BLOB value that this Blob object represents should be truncated
      Throws:
      SQLException - Feature not implemented for now.

    • free

      public void free() throws SQLException
      This method frees the Blob object and releases the resources that it holds. The object is invalid once the free method is called. If free is called multiple times, the subsequent calls to free are treated as a no-op.
      Specified by:
      free in interface Blob
      Specified by:
      free in interface EngineLOB
      Throws:
      SQLException - if an error occurs releasing the Blob's resources

    • getBinaryStream

      public InputStream getBinaryStream(long pos, long length) throws SQLException
      Returns an InputStream object that contains a partial Blob value, starting with the byte specified by pos, which is length bytes in length.
      Specified by:
      getBinaryStream in interface Blob
      Parameters:
      pos - the offset to the first byte of the partial value to be retrieved. The first byte in the Blob is at position 1
      length - the length in bytes of the partial value to be retrieved
      Returns:
      through which the partial Blob value can be read.
      Throws:
      SQLException - if pos is less than 1 or if pos is greater than the number of bytes in the Blob or if pos + length is greater than Blob.length() +1

    • checkValidity

      private void checkValidity() throws SQLException
      Throws:
      SQLException

    • isMaterialized

      boolean isMaterialized()
      Returns if blob data is stored locally (using LOBStreamControl).
      Returns:
      true if materialized else false

    • getLocator

      public int getLocator()
      Return locator for this lob.
      Specified by:
      getLocator in interface EngineLOB
      Returns:
      The locator identifying this lob.