Class EmbedClob

java.lang.Object
org.apache.derby.impl.jdbc.ConnectionChild
org.apache.derby.impl.jdbc.EmbedClob
All Implemented Interfaces:
Clob, EngineLOB
final class EmbedClob extends ConnectionChild implements Clob, EngineLOB
Implements java.sql.Clob (see the JDBC 2.0 spec). A clob sits on top of a CHAR, VARCHAR or LONG VARCHAR column. If its data is small (less than 1 page) it is a byte array taken from the SQLChar 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 can be returned to the user in the getAsciiStream() 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 getAsciiStream()) at the same time as calling the Clob methods.

Supports

  • JSR169 - no subsetting for java.sql.Clob
  • 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

    • clob

      private InternalClob clob
      The underlying Clob object, which may change depending on what the user does with the Clob.

    • isValid

      private boolean isValid
      Tells whether the Clob has been freed or not.

    • locator

      private int locator

  • Constructor Details

  • Method Details

    • length

      public long length() throws SQLException
      Returns the number of characters in the CLOB value designated by this Clob object.
      Specified by:
      length in interface Clob
      Returns:
      The length of the CLOB in number of characters.
      Throws:
      SQLException - if obtaining the length fails

    • getSubString

      public String getSubString(long pos, int length) throws SQLException
      Returns a copy of the specified substring in the CLOB value designated by this Clob object.

      The substring begins at position pos and has up to * length consecutive characters. The starting position must be between 1 and the length of the CLOB plus 1. This allows for zero-length CLOB values, from which only zero-length substrings can be returned.

      If a larger length is requested than there are characters available, characters from the start position to the end of the CLOB are returned.

      NOTE: If the starting position is the length of the CLOB plus 1, zero characters are returned regardless of the length requested.

      Specified by:
      getSubString in interface Clob
      Parameters:
      pos - the first character of the substring to be extracted. The first character is at position 1.
      length - the number of consecutive characters to be copied
      Returns:
      A String that is the specified substring in the CLOB value designated by this Clob object
      Throws:
      SQLException - if there is an error accessing the CLOB

    • getCharacterStream

      public Reader getCharacterStream() throws SQLException
      Gets the Clob contents as a stream of characters.
      Specified by:
      getCharacterStream in interface Clob
      Returns:
      A character stream containing the CLOB data.
      Throws:
      SQLException - if there is an error accessing the CLOB

    • getAsciiStream

      public InputStream getAsciiStream() throws SQLException
      Gets the CLOB value designated by this Clob object as a stream of Ascii bytes.
      Specified by:
      getAsciiStream in interface Clob
      Returns:
      An Ascii stream containing the CLOB data. Valid values in the stream are 0 - 255.
      Throws:
      SQLException - if there is an error accessing the CLOB value

    • position

      public long position(String searchStr, long start) throws SQLException
      Determines the character position at which the specified substring searchStr appears in the CLOB value.

      The search begins at position start. The method uses the following algorithm for the search:

      If the CLOB value is materialized as a string, use String.indexOf.

      If the CLOB value is represented as a stream, read a block of chars from the start position and compare the chars with searchStr. Then:

      • If a matching char is found, increment matchCount.
      • If matchCount is equal to the length of searchStr, return with the current start position.
      • If no match is found, and there is more data, restart search (see below).
      • If no match is found, return -1.

      The position where the stream has a char equal to the first char of searchStr will be remembered and used as the starting position for the next search-iteration if the current match fails. If a non-matching char is found, start a fresh search from the position remembered. If there is no such position, next search will start at the current position +1.

      Specified by:
      position in interface Clob
      Parameters:
      searchStr - the substring for which to search
      start - the position at which to begin searching; the first position is 1
      Returns:
      The position at which the substring appears, -1 if it does not appear in the CLOB value. The first position is 1.
      Throws:
      SQLException - if there is an error accessing the CLOB value

    • position

      public long position(Clob searchClob, long start) throws SQLException
      Determines the character position at which the specified Clob object searchstr appears in this Clob object. The search begins at position start.
      Specified by:
      position in interface Clob
      Parameters:
      searchClob - the Clob object for which to search
      start - the position at which to begin searching; the first position is 1
      Returns:
      the position at which the Clob object appears, else -1; the first position is 1
      Throws:
      SQLException - if there is an error accessing the CLOB value

    • setString

      public int setString(long pos, String str) throws SQLException
      JDBC 3.0 Writes the given Java String to the CLOB value that this Clob object designates at the position pos.
      Specified by:
      setString in interface Clob
      Parameters:
      pos - the position at which to start writing to the CLOB value that this Clob object represents
      Returns:
      the number of characters written
      Throws:
      SQLException - if writing the string fails

    • setString

      public int setString(long pos, String str, int offset, int len) throws SQLException
      JDBC 3.0 Writes len characters of str, starting at character offset, to the CLOB value that this Clob represents.
      Specified by:
      setString in interface Clob
      Parameters:
      pos - the position at which to start writing to this Clob object
      str - the string to be written to the CLOB value that this Clob designates
      offset - the offset into str to start reading the characters to be written
      len - the number of characters to be written
      Returns:
      the number of characters written
      Throws:
      SQLException - if writing the string fails

    • setAsciiStream

      public OutputStream setAsciiStream(long pos) throws SQLException
      JDBC 3.0 Retrieves a stream to be used to write Ascii characters to the CLOB value that this Clob object represents, starting at position pos.
      Specified by:
      setAsciiStream in interface Clob
      Parameters:
      pos - the position at which to start writing to this Clob object
      Returns:
      the stream to which ASCII encoded characters can be written
      Throws:
      SQLException - if obtaining the stream fails

    • setCharacterStream

      public Writer setCharacterStream(long pos) throws SQLException
      JDBC 3.0 Retrieves a stream to be used to write a stream of characters to the CLOB value that this Clob object represents, starting at position pos.
      Specified by:
      setCharacterStream in interface Clob
      Parameters:
      pos - the position at which to start writing to this Clob object
      Returns:
      the stream to which Unicode encoded characters can be written
      Throws:
      SQLException - if obtaining the stream fails

    • truncate

      public void truncate(long len) throws SQLException
      JDBC 3.0 Truncates the CLOB value that this Clob designates to have a length of len characters
      Specified by:
      truncate in interface Clob
      Parameters:
      len - the length, in characters, to which the CLOB value should be truncated, 0 is accepted
      Throws:
      SQLException - if truncating the CLOB value fails

    • free

      public void free() throws SQLException
      Frees the Clob 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 Clob
      Specified by:
      free in interface EngineLOB
      Throws:
      SQLException - if an error occurs releasing the Clobs resources

    • getCharacterStream

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

    • checkValidity

      private void checkValidity() throws SQLException
      Throws:
      SQLException

    • makeWritableClobClone

      private void makeWritableClobClone() throws IOException, SQLException
      Makes a writable clone of the current Clob.

      This is called when we have a StoreStreamClob and the user calls a method updating the content of the Clob. A temporary Clob will then be created to hold the updated content.

      Throws:
      IOException - if accessing underlying I/O resources fail
      SQLException - if accessing underlying resources fail

    • makeWritableClobClone

      private void makeWritableClobClone(long len) throws IOException, SQLException
      Makes a writable clone of the current Clob.

      This is called when we have a StoreStreamClob and the user calls a method updating the content of the Clob. A temporary Clob will then be created to hold the updated content.

      Parameters:
      len - number of characters to be cloned (should be smaller than clob length)
      Throws:
      IOException - if accessing underlying I/O resources fail
      SQLException - if accessing underlying resources fail

    • getInternalClob

      InternalClob getInternalClob()
      Returns the current internal Clob representation.

      Care should be taken, as the representation can change when the user performs operations on the Clob. An example is if the Clob content is served from a store stream and the user updates the content. The internal representation will then be changed to a temporary Clob copy that allows updates.

      Returns:
      The current internal Clob representation.

    • getLocator

      public int getLocator()
      Description copied from interface: EngineLOB
      Returns LOB locator key.

      The key can be used with EmbedConnection.getLOBMapping(int) to retrieve this LOB at a later time.

      Specified by:
      getLocator in interface EngineLOB
      Returns:
      locator value for this Clob.