Class ClobStreamHeaderGenerator

java.lang.Object
org.apache.derby.iapi.types.ClobStreamHeaderGenerator
All Implemented Interfaces:
StreamHeaderGenerator
public final class ClobStreamHeaderGenerator extends Object implements StreamHeaderGenerator
Generates stream headers for Clob data values.

THREAD SAFETY NOTE: This class is considered thread safe, even though it strictly speaking isn't. However, with the assumption that an instance of this class cannot be shared across databases with different versions, the only bad thing that can happen is that the mode is obtained several times.

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private final StringDataValue
    callbackDVD
    Reference to "owning" DVD, used to update it with information about which header format should be used.
    private static final CharStreamHeaderGenerator
    CHARHDRGEN
    Header generator for the pre 10.5 header format.
    private Boolean
    isPreDerbyTenFive
    true if the database version is prior to 10.5, false if the version is 10.5 or newer.
    private static final byte
    MAGIC_BYTE
    Magic byte for the 10.5 stream header format.
    private static final byte[]
    UNKNOWN_LENGTH
    Bytes for a 10.5 unknown length header.

  • Constructor Summary

    Constructors
    Constructor
    Description
    ClobStreamHeaderGenerator(boolean isPreDerbyTenFive)
    Creates a new generator using the specified header format.
    ClobStreamHeaderGenerator(StringDataValue dvd)
    Creates a new generator that will use the context manager to determine which header format to use based on the database version.

  • Method Summary

    Modifier and Type
    Method
    Description
    private void
    determineHeaderFormat()
    Determines which header format to use.
    boolean
    expectsCharCount()
    Tells if the header encodes a character or byte count.
    int
    generateInto(byte[] buf, int offset, long valueLength)
    Generates the header for the specified length and writes it into the provided buffer, starting at the specified offset.
    int
    generateInto(ObjectOutput out, long valueLength)
    Generates the header for the specified length.
    private static Context
    getContext(String contextID)
    Privileged lookup of a Context.
    int
    getMaxHeaderLength()
    Returns the maximum header length.
    int
    writeEOF(byte[] buffer, int offset, long valueLength)
    Writes a Derby-specific end-of-stream marker to the buffer for a stream of the specified character length, if required.
    int
    writeEOF(ObjectOutput out, long valueLength)
    Writes a Derby-specific end-of-stream marker to the destination stream for the specified character length, if required.

    Methods inherited from class Object

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

  • Field Details

    • MAGIC_BYTE

      private static final byte MAGIC_BYTE
      Magic byte for the 10.5 stream header format.
      See Also:

    • UNKNOWN_LENGTH

      private static final byte[] UNKNOWN_LENGTH
      Bytes for a 10.5 unknown length header.

    • CHARHDRGEN

      private static final CharStreamHeaderGenerator CHARHDRGEN
      Header generator for the pre 10.5 header format. This format is used for Clobs as well if the database version is pre 10.5.

    • callbackDVD

      private final StringDataValue callbackDVD
      Reference to "owning" DVD, used to update it with information about which header format should be used. This is currently only determined by consulting the data dictionary about the version.

      This is an optimization to avoid having to consult the data dictionary on every request to generate a header when a data value descriptor is reused.

    • isPreDerbyTenFive

      private Boolean isPreDerbyTenFive
      true if the database version is prior to 10.5, false if the version is 10.5 or newer. If null, the version will be determined by obtaining the database context through the context service.

  • Constructor Details

    • ClobStreamHeaderGenerator

      public ClobStreamHeaderGenerator(StringDataValue dvd)
      Creates a new generator that will use the context manager to determine which header format to use based on the database version.
      Parameters:
      dvd - the owning data value descriptor

    • ClobStreamHeaderGenerator

      public ClobStreamHeaderGenerator(boolean isPreDerbyTenFive)
      Creates a new generator using the specified header format.
      Parameters:
      isPreDerbyTenFive - true if the database version is prior to 10.5, false if the version is 10.5 or newer

  • Method Details

    • expectsCharCount

      public boolean expectsCharCount()
      Tells if the header encodes a character or byte count.

      Currently the header expects a character count if the header format is 10.5 (or newer), and a byte count if we are accessing a database created by a version prior to 10.5.

      Specified by:
      expectsCharCount in interface StreamHeaderGenerator
      Returns:
      false if a byte count is expected (prior to 10.5), true if a character count is expected (10.5 and newer).

    • generateInto

      public int generateInto(byte[] buf, int offset, long valueLength)
      Generates the header for the specified length and writes it into the provided buffer, starting at the specified offset.
      Specified by:
      generateInto in interface StreamHeaderGenerator
      Parameters:
      buf - the buffer to write into
      offset - starting offset in the buffer
      valueLength - the length to encode in the header
      Returns:
      The number of bytes written into the buffer.

    • generateInto

      public int generateInto(ObjectOutput out, long valueLength) throws IOException
      Generates the header for the specified length.
      Specified by:
      generateInto in interface StreamHeaderGenerator
      Parameters:
      out - the destination stream
      valueLength - the length to encode in the header
      Returns:
      The number of bytes written to the destination stream.
      Throws:
      IOException - if writing to the destination stream fails

    • writeEOF

      public int writeEOF(byte[] buffer, int offset, long valueLength)
      Writes a Derby-specific end-of-stream marker to the buffer for a stream of the specified character length, if required.
      Specified by:
      writeEOF in interface StreamHeaderGenerator
      Parameters:
      buffer - the buffer to write into
      offset - starting offset in the buffer
      valueLength - the length of the stream
      Returns:
      Number of bytes written (zero or more).

    • writeEOF

      public int writeEOF(ObjectOutput out, long valueLength) throws IOException
      Writes a Derby-specific end-of-stream marker to the destination stream for the specified character length, if required.
      Specified by:
      writeEOF in interface StreamHeaderGenerator
      Parameters:
      out - the destination stream
      valueLength - the length of the stream
      Returns:
      Number of bytes written (zero or more).
      Throws:
      IOException - if writing to the destination stream fails

    • getMaxHeaderLength

      public int getMaxHeaderLength()
      Returns the maximum header length.
      Specified by:
      getMaxHeaderLength in interface StreamHeaderGenerator
      Returns:
      Maximum header length in bytes.

    • determineHeaderFormat

      private void determineHeaderFormat()
      Determines which header format to use.

      Implementation note: The header format is determined by consulting the data dictionary throught the context service. If there is no context, the operation will fail.

      Throws:
      IllegalStateException - if there is no context

    • getContext

      private static Context getContext(String contextID)
      Privileged lookup of a Context. Must be private so that user code can't call this entry point.