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org.hsqldb.jdbc
Class JDBCClobFile

java.lang.Object
  extended by org.hsqldb.jdbc.JDBCClobFile
All Implemented Interfaces:
Clob
public class JDBCClobFile
extends Object
implements Clob

HSQLDB-Specific Information:

Starting with 2.1, in addition to HSQLDB driver support for both client-side in-memory and remote SQL CLOB data implementations, this class is provided to expose efficient, relatively high-performance CLOB operations over client accessible files.

Design Notes

Although it is possible to implement a transactional version of this class, the present implementation directly propagates changes to the underlying file such that changes become visible as soon as they are either implicitly or explicitly flushed to disk.

Since:
HSQLDB 2.1
Author:
boucherb@users

Field Summary
static String TEMP_FILE_PREFIX
           
static String TEMP_FILE_SUFFIX
           
 
Constructor Summary
JDBCClobFile()
          Convenience constructor for JDBCClobFile((String)null).
JDBCClobFile(File file)
          Convenience constructor for JDBCClobFile(file,null).
JDBCClobFile(File file, String encoding)
          Constructs a new JDBCClobFile instance backed by the given File object using the given encoding to read and write file content.
JDBCClobFile(String encoding)
          Constructs a new JDBCClobFile instance backed by an File object created by File.createTempFile(TEMP_FILE_PREFIX, TEMP_FILE_SUFFIX), using the given encoding to read and write file content.
 
Method Summary
 void free()
          This method frees the Clob object and releases the resources the resources that it holds.
 InputStream getAsciiStream()
          Retrieves the CLOB value designated by this Clob object as an ascii stream.
 Reader getCharacterStream()
          Retrieves the CLOB value designated by this Clob object as a java.io.Reader object (or as a stream of characters).
 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.
 String getEncoding()
           
 File getFile()
          Retrieves the canonical File object denoting the file that backs this CLOB.
 String getSubString(long pos, int length)
          Retrieves a copy of the specified substring in the CLOB value designated by this Clob object.
 boolean isDeleteOnFree()
          Retrieves whether an attempt to delete the backing file is made in response to invocation of free().
 long length()
          Retrieves the number of characters in the CLOB value designated by this Clob object.
 long position(char[] pattern, long start)
          Retrieves the character position at which the specified char[] pattern appears in the CLOB value represented by this Clob object.
 long position(Clob pattern, long start)
          Retrieves the character position at which the specified Clob object searchstr appears in this Clob object.
 long position(String searchstr, long start)
          Retrieves the character position at which the specified Clob object searchstr appears in this Clob object.
 OutputStream setAsciiStream(long pos)
          Retrieves a stream to be used to write Ascii characters to the CLOB value that this Clob object represents, starting at position pos.
 Writer setCharacterStream(long pos)
          Retrieves a stream to be used to write a stream of Unicode characters to the CLOB value that this Clob object represents, at position pos.
 void setDeleteOnFree(boolean deleteOnFree)
          Assigns whether an attempt to delete the backing file is made in response to invocation of free().
 int setString(long pos, String str)
          Writes the given Java String to the CLOB value that this Clob object designates at the position pos.
 int setString(long pos, String str, int offset, int len)
          Writes len characters of str, starting at character offset, to the CLOB value that this Clob represents.
 void truncate(long len)
          Truncates the CLOB value that this Clob designates to have a length of len characters.
 
Methods inherited from class java.lang.Object
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

TEMP_FILE_PREFIX

public static final String TEMP_FILE_PREFIX
See Also:
Constant Field Values

TEMP_FILE_SUFFIX

public static final String TEMP_FILE_SUFFIX
See Also:
Constant Field Values
Constructor Detail

JDBCClobFile

public JDBCClobFile()
             throws SQLException
Convenience constructor for JDBCClobFile((String)null).

Throws:
SQLException - if the platform encoding is unsupported, the temp file cannot be created or some other error occurs that prevents the construction of a valid instance of this class.

JDBCClobFile

public JDBCClobFile(String encoding)
             throws SQLException
Constructs a new JDBCClobFile instance backed by an File object created by File.createTempFile(TEMP_FILE_PREFIX, TEMP_FILE_SUFFIX), using the given encoding to read and write file content.

Parameters:
encoding - the name of the character encoding used to read and write character data in the underlying file, as well as to determine the character length of and character offsets into the underlying file. Specify null to denote the platform encoding.
Throws:
SQLException - if the given encoding is unsupported, the backing temp file could not be created or if a security manager exists and its SecurityManager.checkWrite(java.lang.String) method does not allow a file to be created.

JDBCClobFile

public JDBCClobFile(File file)
             throws SQLException
Convenience constructor for JDBCClobFile(file,null).

Parameters:
file - that is to back the new CLOB instance.
Throws:
SQLException - if an I/O error occurs, which is possible because the construction of the canonical pathname may require file-system queries; a required system property value cannot be accessed; a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the file

JDBCClobFile

public JDBCClobFile(File file,
                    String encoding)
             throws SQLException
Constructs a new JDBCClobFile instance backed by the given File object using the given encoding to read and write file content.

Parameters:
file - that is to back the new CLOB instance.
encoding - the name of the character encoding used to read and write character data in the underlying file, as well as to determine the character length of and character offsets into the underlying file. Specify null to denote the platform encoding.
Throws:
SQLException - if the given encoding is unsupported; an I/O error occurs, which is possible because the construction of the canonical pathname may require file-system queries; a required system property value cannot be accessed; a security manager exists and its SecurityManager.checkRead(java.io.FileDescriptor) method denies read access to the file
Method Detail

length

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

Specified by:
length in interface Clob
Returns:
length of the CLOB in characters
Throws:
SQLException - if there is an error accessing the length of the CLOB value
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
Since:
JDK 1.2

getSubString

public String getSubString(long pos,
                           int length)
                    throws SQLException
Retrieves 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.

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; the value for length must be 0 or greater
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 value; if pos is less than 1 or length is less than 0
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
Since:
JDK 1.2

getCharacterStream

public Reader getCharacterStream()
                          throws SQLException
Retrieves the CLOB value designated by this Clob object as a java.io.Reader object (or as a stream of characters).

Specified by:
getCharacterStream in interface Clob
Returns:
a java.io.Reader object containing the CLOB data
Throws:
SQLException - if there is an error accessing the CLOB value
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
Since:
JDK 1.2
See Also:
setCharacterStream(long)

getAsciiStream

public InputStream getAsciiStream()
                           throws SQLException
Retrieves the CLOB value designated by this Clob object as an ascii stream.

Specified by:
getAsciiStream in interface Clob
Returns:
a java.io.InputStream object containing the CLOB data
Throws:
SQLException - if there is an error accessing the CLOB value
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
Since:
JDK 1.2
See Also:
setAsciiStream(long)

position

public long position(char[] pattern,
                     long start)
              throws SQLException
Retrieves the character position at which the specified char[] pattern appears in the CLOB value represented by this Clob object. The search begins at position start.

Parameters:
pattern - 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 or -1 if it is not present; the first position is 1
Throws:
SQLException - if there is an error accessing the CLOB value or if pos is less than 1
SQLFeatureNotSupportedException - if the JDBC driver does not support this method

position

public long position(String searchstr,
                     long start)
              throws SQLException
Retrieves 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:
searchstr - 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 or -1 if it is not present; the first position is 1
Throws:
SQLException - if there is an error accessing the CLOB value or if start is less than 1
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
Since:
JDK 1.2

position

public long position(Clob pattern,
                     long start)
              throws SQLException
Retrieves 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:
pattern - 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 or -1 if it is not present; the first position is 1
Throws:
SQLException - if there is an error accessing the CLOB value or if start is less than 1
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
Since:
JDK 1.2

setString

public int setString(long pos,
                     String str)
              throws SQLException
Writes the given Java String to the CLOB value that this Clob object designates at the position pos. The string will overwrite the existing characters in the Clob object starting at the position pos. If the end of the Clob value is reached while writing the given string, then the length of the Clob value will be increased to accommodate the extra characters.

Note: If the value specified for pos is greater then the length+1 of the CLOB value then the behavior is undefined. Some JDBC drivers may throw a SQLException while other drivers may support this operation.

Specified by:
setString in interface Clob
Parameters:
pos - the position at which to start writing to the CLOB value that this Clob object represents; The first position is 1
str - the string to be written to the CLOB value that this Clob designates
Returns:
the number of characters written
Throws:
SQLException - if there is an error accessing the CLOB value or if pos is less than 1
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
Since:
JDK 1.4

setString

public int setString(long pos,
                     String str,
                     int offset,
                     int len)
              throws SQLException
Writes len characters of str, starting at character offset, to the CLOB value that this Clob represents. The string will overwrite the existing characters in the Clob object starting at the position pos. If the end of the Clob value is reached while writing the given string, then the length of the Clob value will be increased to accommodate the extra characters.

Note: If the value specified for pos is greater then the length+1 of the CLOB value then the behavior is undefined. Some JDBC drivers may throw a SQLException while other drivers may support this operation.

Specified by:
setString in interface Clob
Parameters:
pos - the position at which to start writing to this CLOB object; The first position is 1
str - the string to be written to the CLOB value that this Clob object represents
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 there is an error accessing the CLOB value or if pos is less than 1
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
Since:
JDK 1.4

setAsciiStream

public OutputStream setAsciiStream(long pos)
                            throws SQLException
Retrieves a stream to be used to write Ascii characters to the CLOB value that this Clob object represents, starting at position pos. Characters written to the stream will overwrite the existing characters in the Clob object starting at the position pos. If the end of the Clob value is reached while writing characters to the stream, then the length of the Clob value will be increased to accommodate the extra characters.

Note: If the value specified for pos is greater then the length+1 of the CLOB value then the behavior is undefined. Some JDBC drivers may throw a SQLException while other drivers may support this operation.

Specified by:
setAsciiStream in interface Clob
Parameters:
pos - the position at which to start writing to this CLOB object; The first position is 1
Returns:
the stream to which ASCII encoded characters can be written
Throws:
SQLException - if there is an error accessing the CLOB value or if pos is less than 1
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
Since:
JDK 1.4
See Also:
getAsciiStream()

setCharacterStream

public Writer setCharacterStream(long pos)
                          throws SQLException
Retrieves a stream to be used to write a stream of Unicode characters to the CLOB value that this Clob object represents, at position pos. Characters written to the stream will overwrite the existing characters in the Clob object starting at the position pos. If the end of the Clob value is reached while writing characters to the stream, then the length of the Clob value will be increased to accommodate the extra characters.

Note: If the value specified for pos is greater then the length+1 of the CLOB value then the behavior is undefined. Some JDBC drivers may throw a SQLException while other drivers may support this operation.

Specified by:
setCharacterStream in interface Clob
Parameters:
pos - the position at which to start writing to the CLOB value; The first position is 1
Returns:
a stream to which Unicode encoded characters can be written
Throws:
SQLException - if there is an error accessing the CLOB value or if pos is less than 1
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
Since:
JDK 1.4
See Also:
getCharacterStream()

truncate

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

Note: If the value specified for pos is greater then the length+1 of the CLOB value then the behavior is undefined. Some JDBC drivers may throw a SQLException while other drivers may support this operation.

Specified by:
truncate in interface Clob
Parameters:
len - the length, in characters, to which the CLOB value should be truncated
Throws:
SQLException - if there is an error accessing the CLOB value or if len is less than 0
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
Since:
JDK 1.4

free

public void free()
          throws SQLException
This method frees the Clob object and releases the resources the resources that it holds. The object is invalid once the free method is called.

After free has been called, any attempt to invoke a method other than free will result in a SQLException being thrown. If free is called multiple times, the subsequent calls to free are treated as a no-op.

Specified by:
free in interface Clob
Throws:
SQLException - if an error occurs releasing the Clob's resources
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
Since:
JDK 1.4

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 the number of characters in the Clob
SQLFeatureNotSupportedException - if the JDBC driver does not support this method
Since:
1.6

getFile

public File getFile()
Retrieves the canonical File object denoting the file that backs this CLOB.

Returns:
the file that backs this CLOB.

getEncoding

public String getEncoding()
Returns:
the name of the character encoding used to read and write character data in the underlying files, as well as to determine the character length and character offsets into the underlying file

isDeleteOnFree

public boolean isDeleteOnFree()
Retrieves whether an attempt to delete the backing file is made in response to invocation of free().

Returns:
true if backing file deletion is attempted; otherwise false.

setDeleteOnFree

public void setDeleteOnFree(boolean deleteOnFree)
Assigns whether an attempt to delete the backing file is made in response to invocation of free().

Parameters:
deleteOnFree - the new value to assign
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