Class StoreStreamClob

java.lang.Object
org.apache.derby.impl.jdbc.StoreStreamClob
All Implemented Interfaces:
InternalClob
final class StoreStreamClob extends Object implements InternalClob
A read-only Clob representation operating on streams out of the Derby store module.

Note that the streams from the store are expected to have the following properties:

  1. The first few bytes are used for length encoding. Currently the number of bytes is either 2 or 5.
  2. A Derby-specific end-of-stream marker at the end of the stream can be present. The marker is expected to be 0xe0 0x00 0x00

  • Field Details

    • released

      private volatile boolean released
      Tells whether this Clob has been released or not.

    • positionedStoreStream

      private final PositionedStoreStream positionedStoreStream
      The stream from store, used to read bytes from the database.

      To be able to support the requirements, the stream must implement Resetable.

    • csd

      private CharacterStreamDescriptor csd
      The descriptor used to describe the underlying source stream.

    • conChild

      private final ConnectionChild conChild
      The connection (child) this Clob belongs to.

    • synchronizationObject

      private final Object synchronizationObject
      Object used for synchronizing access to the store stream.

    • internalReader

      private UTF8Reader internalReader
      Shared internal reader, closed when the Clob is released. This is a performance optimization, and the stream is shared between "one time" operations, for instance getSubString calls. Often a subset, or the whole, of the Clob is read subsequently and then this optimization avoids repositioning costs (the store does not support random access for LOBs). NOTE: Do not publish this reader to the end-user.

    • unclosableInternalReader

      private FilterReader unclosableInternalReader
      The internal reader wrapped so that it cannot be closed.

  • Constructor Details

    • StoreStreamClob

      public StoreStreamClob(CharacterStreamDescriptor csd, ConnectionChild conChild) throws StandardException
      Creates a new Clob based on a stream from store.

      The stream used as a source for this Clob has to implement the interface Resetable, as the stream interface from store only allows for movement forwards. If the stream has been advanced too far with regards to the user request, the stream must be reset and we start from the beginning.

      Parameters:
      csd - descriptor for the source stream, including a reference to it
      conChild - the connection (child) this Clob belongs to
      Throws:
      StandardException

  • Method Details

    • release

      public void release()
      Releases resources associated with this Clob.
      Specified by:
      release in interface InternalClob

    • getCharLength

      public long getCharLength() throws SQLException
      Returns the number of characters in the Clob.
      Specified by:
      getCharLength in interface InternalClob
      Returns:
      Number of characters in the Clob.
      Throws:
      SQLException - if any kind of error is encountered, be it related to I/O or something else

    • getCharLengthIfKnown

      public long getCharLengthIfKnown()
      Returns the cached character count for the Clob, if any.
      Specified by:
      getCharLengthIfKnown in interface InternalClob
      Returns:
      The number of characters in the Clob, or -1 if unknown.

    • getRawByteStream

      public InputStream getRawByteStream() throws IOException, SQLException
      Returns a stream serving the raw bytes of this Clob.

      Note that the stream returned is an internal stream, and it should not be pulished to end users.

      Specified by:
      getRawByteStream in interface InternalClob
      Returns:
      A stream serving the bytes of this Clob, initialized at byte 0 of the data. The buffer must be assumed to be unbuffered, but no such guarantee is made.
      Throws:
      IOException - if accessing the I/O resources fail
      SQLException - if accessing the store resources fail

    • getReader

      public Reader getReader(long pos) throws IOException, SQLException
      Returns a reader for the Clob, initialized at the specified character position.
      Specified by:
      getReader in interface InternalClob
      Parameters:
      pos - character position. The first character is at position 1.
      Returns:
      A reader initialized at the specified position.
      Throws:
      EOFException - if the positions is larger than the Clob
      IOException - if accessing the I/O resources fail
      SQLException - if accessing the store resources fail

    • getInternalReader

      public Reader getInternalReader(long characterPosition) throws IOException, SQLException
      Returns an internal reader for the Clob, initialized at the specified character position.
      Specified by:
      getInternalReader in interface InternalClob
      Parameters:
      characterPosition - 1-based character position.
      Returns:
      A reader initialized at the specified position.
      Throws:
      EOFException - if the positions is larger than the Clob
      IOException - if accessing the I/O resources fail
      SQLException - if accessing the store resources fail

    • getUpdateCount

      public long getUpdateCount()
      Returns the update count of this Clob.

      Always returns zero, as this Clob cannot be updated.

      Specified by:
      getUpdateCount in interface InternalClob
      Returns:
      Zero (read-only Clob).

    • getWriter

      public Writer getWriter(long pos)
      Not supported.
      Specified by:
      getWriter in interface InternalClob
      Parameters:
      pos - the starting character position. The first character is at position 1.
      Returns:
      A writer initialized at the specified character position.
      See Also:

    • insertString

      public long insertString(String str, long pos)
      Not supported.
      Specified by:
      insertString in interface InternalClob
      Parameters:
      str - the string to insert
      pos - the character position the string will be inserted at. Must be between 1 and clob.length() +1, inclusive.
      Returns:
      The number of characters inserted.
      See Also:

    • isReleased

      public boolean isReleased()
      Tells if this Clob has been released.
      Specified by:
      isReleased in interface InternalClob
      Returns:
      true if released, false if not.

    • isWritable

      public boolean isWritable()
      Tells if this Clob can be modified.
      Specified by:
      isWritable in interface InternalClob
      Returns:
      false, this Clob is read-only.

    • truncate

      public void truncate(long newLength)
      Not supported.
      Specified by:
      truncate in interface InternalClob
      Parameters:
      newLength - the length in characters to truncate to
      See Also:

    • noStateChangeLOB

      private static SQLException noStateChangeLOB(Throwable t)
      Wrap real exception in a SQLException to avoid changing the state of the connection child by cleaning it up.
      Parameters:
      t - real cause of error that we want to "ignore" with respect to transaction context cleanup
      Returns:
      A SQLException wrapped around the real cause of the error

    • checkIfValid

      private void checkIfValid()
      Makes sure the Clob has not been released.

      All operations are invalid on a released Clob.

      Throws:
      IllegalStateException - if the Clob has been released