org.apache.derby.impl.jdbc
Class EmbedClob

java.lang.Object
  extended by org.apache.derby.impl.jdbc.ConnectionChild
      extended by org.apache.derby.impl.jdbc.EmbedClob
All Implemented Interfaces:
java.sql.Clob, EngineLOB

final class EmbedClob
extends ConnectionChild
implements java.sql.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


Field Summary
private  InternalClob clob
          The underlying Clob object, which may change depending on what the user does with the Clob.
private  boolean isValid
          Tells whether the Clob has been freed or not.
private  int locator
           
 
Fields inherited from class org.apache.derby.impl.jdbc.ConnectionChild
factory, localConn
 
Constructor Summary
(package private) EmbedClob(EmbedConnection con)
          Creates an empty Clob object.
protected EmbedClob(EmbedConnection con, StringDataValue dvd)
          Creates a Clob on top of a data value descriptor.
 
Method Summary
private  void checkValidity()
           
 void free()
          Frees the Clob and releases the resources that it holds.
 java.io.InputStream getAsciiStream()
          Gets the CLOB value designated by this Clob object as a stream of Ascii bytes.
 java.io.Reader getCharacterStream()
          Gets the Clob contents as a stream of characters.
 java.io.Reader getCharacterStream(long pos, long length)
          Returns a Reader object that contains a partial Clob value, starting with the character specified by pos, which is length characters in length.
(package private)  InternalClob getInternalClob()
          Returns the current internal Clob representation.
 int getLocator()
          Returns LOB locator key.
 java.lang.String getSubString(long pos, int length)
          Returns a copy of the specified substring in the CLOB value designated by this Clob object.
 long length()
          Returns the number of characters in the CLOB value designated by this Clob object.
private  void makeWritableClobClone()
          Makes a writable clone of the current Clob.
private  void makeWritableClobClone(long len)
          Makes a writable clone of the current Clob.
 long position(java.sql.Clob searchClob, long start)
          Determines the character position at which the specified Clob object searchstr appears in this Clob object.
 long position(java.lang.String searchStr, long start)
          Determines the character position at which the specified substring searchStr appears in the CLOB value.
 java.io.OutputStream setAsciiStream(long pos)
          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.
 java.io.Writer setCharacterStream(long pos)
          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.
 int setString(long pos, java.lang.String str)
          JDBC 3.0 Writes the given Java String to the CLOB value that this Clob object designates at the position pos.
 int setString(long pos, java.lang.String str, int offset, int len)
          JDBC 3.0 Writes len characters of str, starting at character offset, to the CLOB value that this Clob represents.
 void truncate(long len)
          JDBC 3.0 Truncates the CLOB value that this Clob designates to have a length of len characters
 
Methods inherited from class org.apache.derby.impl.jdbc.ConnectionChild
commitIfAutoCommit, commitIfNeeded, getCal, getConnectionSynchronization, getEmbedConnection, handleException, needCommit, newSQLException, newSQLException, newSQLException, restoreContextStack, setupContextStack
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

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 Detail

EmbedClob

EmbedClob(EmbedConnection con)
    throws java.sql.SQLException
Creates an empty Clob object.

Parameters:
con - The Connection object associated with this EmbedClob object.
Throws:
java.sql.SQLException

EmbedClob

protected EmbedClob(EmbedConnection con,
                    StringDataValue dvd)
             throws StandardException
Creates a Clob on top of a data value descriptor.

This constructor should only be called by EmbedResultSet.getClob(int). The data value descriptor may provide a String or a stream as the source of the Clob.

Parameters:
dvd - string data value descriptor providing the Clob source
con - associated connection for the Clob
Throws:
StandardException
Method Detail

length

public long length()
            throws java.sql.SQLException
Returns the number of characters in the CLOB value designated by this Clob object.

Specified by:
length in interface java.sql.Clob
Returns:
The length of the CLOB in number of characters.
Throws:
java.sql.SQLException - if obtaining the length fails

getSubString

public java.lang.String getSubString(long pos,
                                     int length)
                              throws java.sql.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 java.sql.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:
java.sql.SQLException - if there is an error accessing the CLOB

getCharacterStream

public java.io.Reader getCharacterStream()
                                  throws java.sql.SQLException
Gets the Clob contents as a stream of characters.

Specified by:
getCharacterStream in interface java.sql.Clob
Returns:
A character stream containing the CLOB data.
Throws:
java.sql.SQLException - if there is an error accessing the CLOB

getAsciiStream

public java.io.InputStream getAsciiStream()
                                   throws java.sql.SQLException
Gets the CLOB value designated by this Clob object as a stream of Ascii bytes.

Specified by:
getAsciiStream in interface java.sql.Clob
Returns:
An Ascii stream containing the CLOB data. Valid values in the stream are 0 - 255.
Throws:
java.sql.SQLException - if there is an error accessing the CLOB value

position

public long position(java.lang.String searchStr,
                     long start)
              throws java.sql.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:

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 java.sql.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:
java.sql.SQLException - if there is an error accessing the CLOB value

position

public long position(java.sql.Clob searchClob,
                     long start)
              throws java.sql.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 java.sql.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:
java.sql.SQLException - if there is an error accessing the CLOB value

setString

public int setString(long pos,
                     java.lang.String str)
              throws java.sql.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 java.sql.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:
java.sql.SQLException - if writing the string fails

setString

public int setString(long pos,
                     java.lang.String str,
                     int offset,
                     int len)
              throws java.sql.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 java.sql.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:
java.sql.SQLException - if writing the string fails

setAsciiStream

public java.io.OutputStream setAsciiStream(long pos)
                                    throws java.sql.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 java.sql.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:
java.sql.SQLException - if obtaining the stream fails

setCharacterStream

public java.io.Writer setCharacterStream(long pos)
                                  throws java.sql.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 java.sql.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:
java.sql.SQLException - if obtaining the stream fails

truncate

public void truncate(long len)
              throws java.sql.SQLException
JDBC 3.0 Truncates the CLOB value that this Clob designates to have a length of len characters

Specified by:
truncate in interface java.sql.Clob
Parameters:
len - the length, in characters, to which the CLOB value should be truncated, 0 is accepted
Throws:
java.sql.SQLException - if truncating the CLOB value fails

free

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

getCharacterStream

public java.io.Reader getCharacterStream(long pos,
                                         long length)
                                  throws java.sql.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 java.sql.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:
java.sql.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 java.sql.SQLException
Throws:
java.sql.SQLException

makeWritableClobClone

private void makeWritableClobClone()
                            throws java.io.IOException,
                                   java.sql.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:
java.io.IOException - if accessing underlying I/O resources fail
java.sql.SQLException - if accessing underlying resources fail

makeWritableClobClone

private void makeWritableClobClone(long len)
                            throws java.io.IOException,
                                   java.sql.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:
java.io.IOException - if accessing underlying I/O resources fail
java.sql.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.

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