|
||||||||||
| PREV CLASS NEXT CLASS | FRAMES NO FRAMES | |||||||||
| SUMMARY: NESTED | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD | |||||||||
java.lang.Objectorg.hsqldb.jdbc.JDBCClob
public class JDBCClob
The mapping in the JavaTM programming language
for the SQL CLOB type.
An SQL CLOB is a built-in type
that stores a Character Large Object as a column value in a row of
a database table.
By default drivers implement a Clob object using an SQL
locator(CLOB), which means that a Clob object
contains a logical pointer to the SQL CLOB data rather than
the data itself. A Clob object is valid for the duration
of the transaction in which it was created.
The Clob interface provides methods for getting the
length of an SQL CLOB (Character Large Object) value,
for materializing a CLOB value on the client, and for
searching for a substring or CLOB object within a
CLOB value.
Methods in the interfaces ResultSet,
CallableStatement, and PreparedStatement, such as
getClob and setClob allow a programmer to
access an SQL CLOB value. In addition, this interface
has methods for updating a CLOB value.
All methods on the Clob interface must be fully implemented if the
JDBC driver supports the data type.
Previous to 2.0, the HSQLDB driver did not implement Clob using an SQL locator(CLOB). That is, an HSQLDB Clob object did not contain a logical pointer to SQL CLOB data; rather it directly contained a representation of the data (a String). As a result, an HSQLDB Clob object was itself valid beyond the duration of the transaction in which is was created, although it did not necessarily represent a corresponding value on the database. Also, the interface methods for updating a CLOB value were unsupported, with the exception of the truncate method, in that it could be used to truncate the local value.
Starting with 2.0, the HSQLDB driver fully supports both local and remote
SQL CLOB data implementations, meaning that an HSQLDB Clob object may
contain a logical pointer to remote SQL CLOB data (see JDBCClobClient) or it may directly contain a local representation of the
data (as implemented in this class). In particular, when the product is built
under JDK 1.6+ and the Clob instance is constructed as a result of calling
JDBCConnection.createClob(), then the resulting Clob instance is initially
disconnected (is not bound to the transaction scope of the vending Connection
object), the data is contained directly and all interface methods for
updating the CLOB value are supported for local use until the first
invocation of free(); otherwise, an HSQLDB Clob's implementation is
determined at runtime by the driver, it is typically not valid beyond
the duration of the transaction in which is was created, and there no
standard way to query whether it represents a local or remote value.
| Constructor Summary | |
|---|---|
JDBCClob(String data)
Constructs a new JDBCClob object wrapping the given character sequence. |
|
| 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 |
getSubString(long pos,
int length)
Retrieves a copy of the specified substring in the CLOB value
designated by this Clob object. |
long |
length()
Retrieves the number of characters in the CLOB value
designated by this Clob object. |
long |
position(Clob searchstr,
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 substring searchstr appears in the SQL CLOB value
represented by 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. |
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 |
| Constructor Detail |
|---|
public JDBCClob(String data)
throws SQLException
This constructor is used internally to retrieve result set values as Clob objects, yet it must be public to allow access from other packages. As such (in the interest of efficiency) this object maintains a reference to the given String object rather than making a copy and so it is gently suggested (in the interest of effective memory management) that external clients using this constructor either take pause to consider the implications or at least take care to provide a String object whose internal character buffer is not much larger than required to represent the value.
data - the character sequence representing the Clob value
SQLException - if the argument is null| Method Detail |
|---|
public long length()
throws SQLException
CLOB value
designated by this Clob object.
length in interface ClobCLOB in characters
SQLException - if there is an error accessing the
length of the CLOB value
SQLFeatureNotSupportedException - if the JDBC driver does not support
this method
public String getSubString(long pos,
int length)
throws SQLException
CLOB value
designated by this Clob object.
The substring begins at position
pos and has up to length consecutive
characters.
The official specification above is ambiguous in that it does not precisely indicate the policy to be observed when pos > this.length() - length. One policy would be to retrieve the characters from pos to this.length(). Another would be to throw an exception. HSQLDB observes the second policy.
Note
Depending java.lang.String implementation, the returned value may be sharing the underlying (and possibly much larger) character buffer. This facilitates much faster operation and will save memory if many transient substrings are to be retrieved during processing, but it has memory management implications should retrieved substrings be required to survive for any non-trivial duration. It is left up to the client to decide how to handle the trade-off (whether to make an isolated copy of the returned substring or risk that more memory remains allocated than is absolutely required).
getSubString in interface Clobpos - 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;
JDBC 4.1[ the value for length must be 0 or greater]
String that is the specified substring in
the CLOB value designated by this Clob object
SQLException - if there is an error accessing the
CLOB value; if pos is less than 1 JDBC 4.1[or length is
less than 0]
SQLFeatureNotSupportedException - if the JDBC driver does not support
this method
public Reader getCharacterStream()
throws SQLException
CLOB value designated by this Clob
object as a java.io.Reader object (or as a stream of
characters).
getCharacterStream in interface Clobjava.io.Reader object containing the
CLOB data
SQLException - if there is an error accessing the
CLOB value
SQLFeatureNotSupportedException - if the JDBC driver does not support
this methodsetCharacterStream(long)
public InputStream getAsciiStream()
throws SQLException
CLOB value designated by this Clob
object as an ASCII stream.
getAsciiStream in interface Clobjava.io.InputStream object containing the
CLOB data
SQLException - if there is an error accessing the
CLOB value
SQLFeatureNotSupportedException - if the JDBC driver does not support
this methodsetAsciiStream(long)
public long position(String searchstr,
long start)
throws SQLException
searchstr appears in the SQL CLOB value
represented by this Clob object. The search
begins at position start.
position in interface Clobsearchstr - the substring for which to searchstart - the position at which to begin searching; the first position
is 1
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
public long position(Clob searchstr,
long start)
throws SQLException
Clob object searchstr appears in this
Clob object. The search begins at position
start.
position in interface Clobsearchstr - the Clob object for which to searchstart - the position at which to begin searching; the first
position is 1
Clob object appears
or -1 if it is not present; the first position is 1
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
public int setString(long pos,
String str)
throws SQLException
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.
Starting with HSQLDB 2.0 this feature is supported.
When built under JDK 1.6+ and the Clob instance is constructed as a result of calling JDBCConnection.createClob(), this operation affects only the client-side value; it has no effect upon a value stored in the database because JDBCConnection.createClob() constructs disconnected, initially empty Clob instances. To propagate the Clob value to a database in this case, it is required to supply the Clob instance to an updating or inserting setXXX method of a Prepared or Callable Statement, or to supply the Clob instance to an updateXXX method of an updatable ResultSet.
Implementation Notes:
No attempt is made to ensure precise thread safety. Instead, volatile member field and local variable snapshot isolation semantics are implemented. This is expected to eliminate most issues related to race conditions, with the possible exception of concurrent invocation of free().
In general, however, if an application may perform concurrent JDBCClob modifications and the integrity of the application depends on total order Clob modification semantics, then such operations should be synchronized on an appropriate monitor.
setString in interface Clobpos - the position at which to start writing to the CLOB
value that this Clob object represents;
The first position is 1str - the string to be written to the CLOB
value that this Clob designates
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
public int setString(long pos,
String str,
int offset,
int len)
throws SQLException
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.
Starting with HSQLDB 2.0 this feature is supported.
When built under JDK 1.6+ and the Clob instance is constructed as a result of calling JDBCConnection.createClob(), this operation affects only the client-side value; it has no effect upon a value stored in a database because JDBCConnection.createClob() constructs disconnected, initially empty Clob instances. To propagate the Clob value to a database in this case, it is required to supply the Clob instance to an updating or inserting setXXX method of a Prepared or Callable Statement, or to supply the Clob instance to an updateXXX method of an updatable ResultSet.
Implementation Notes:
If the value specified for pos
is greater than the length of the CLOB value, then
the CLOB value is extended in length to accept the
written characters and the undefined region up to pos is
filled with (char)0.
No attempt is made to ensure precise thread safety. Instead, volatile member field and local variable snapshot isolation semantics are implemented. This is expected to eliminate most issues related to race conditions, with the possible exception of concurrent invocation of free().
In general, however, if an application may perform concurrent JDBCClob modifications and the integrity of the application depends on total order Clob modification semantics, then such operations should be synchronized on an appropriate monitor.
setString in interface Clobpos - the position at which to start writing to this
CLOB object; The first position is 1str - the string to be written to the CLOB
value that this Clob object representsoffset - the offset into str to start reading
the characters to be writtenlen - the number of characters to be written
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
public OutputStream setAsciiStream(long pos)
throws SQLException
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 than the length of the CLOB value, then the
behavior is undefined. Some JDBC drivers may throw a
SQLException while other drivers may support this
operation.
Starting with HSQLDB 2.0 this feature is supported.
When built under JDK 1.6+ and the Clob instance is constructed as a result of calling JDBCConnection.createClob(), this operation affects only the client-side value; it has no effect upon a value stored in a database because JDBCConnection.createClob() constructs disconnected, initially empty Clob instances. To propagate the Clob value to a database in this case, it is required to supply the Clob instance to an updating or inserting setXXX method of a Prepared or Callable Statement, or to supply the Clob instance to an updateXXX method of an updatable ResultSet.
Implementation Notes:
The data written to the stream does not appear in this Clob until the stream is closed.
When the stream is closed, if the value specified for pos
is greater than the length of the CLOB value, then
the CLOB value is extended in length to accept the
written characters and the undefined region up to pos is
filled with (char)0.
Also, no attempt is made to ensure precise thread safety. Instead, volatile member field and local variable snapshot isolation semantics are implemented. This is expected to eliminate most issues related to race conditions, with the possible exception of concurrent invocation of free().
In general, however, if an application may perform concurrent JDBCClob modifications and the integrity of the application depends on total order Clob modification semantics, then such operations should be synchronized on an appropriate monitor.
setAsciiStream in interface Clobpos - the position at which to start writing to this
CLOB object; The first position is 1
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 methodgetAsciiStream()
public Writer setCharacterStream(long pos)
throws SQLException
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.
Starting with HSQLDB 2.0 this feature is supported.
When built under JDK 1.6+ and the Clob instance is constructed as a result of calling JDBCConnection.createClob(), this operation affects only the client-side value; it has no effect upon a value stored in a database because JDBCConnection.createClob() constructs disconnected, initially empty Clob instances. To propagate the Clob value to a database in this case, it is required to supply the Clob instance to an updating or inserting setXXX method of a Prepared or Callable Statement, or to supply the Clob instance to an updateXXX method of an updatable ResultSet.
Implementation Notes:
The data written to the stream does not appear in this Clob until the stream is closed.
When the stream is closed, if the value specified for pos
is greater than the length of the CLOB value, then
the CLOB value is extended in length to accept the
written characters and the undefined region up to pos is
filled with (char)0.
Also, no attempt is made to ensure precise thread safety. Instead, volatile member field and local variable snapshot isolation semantics are implemented. This is expected to eliminate most issues related to race conditions, with the possible exception of concurrent invocation of free().
In general, however, if an application may perform concurrent JDBCClob modifications and the integrity of the application depends on total order Clob modification semantics, then such operations should be synchronized on an appropriate monitor.
setCharacterStream in interface Clobpos - the position at which to start writing to the
CLOB value; The first position is 1
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 methodgetCharacterStream()
public void truncate(long len)
throws SQLException
CLOB value that this Clob
designates to have a length of len
characters.
Note: If the value specified for len
is greater than the length of the CLOB value, then the
behavior is undefined. Some JDBC drivers may throw a
SQLException while other drivers may support this
operation.
Starting with HSQLDB 2.0 this feature is fully supported.
When built under JDK 1.6+ and the Clob instance is constructed as a result of calling JDBCConnection.createClob(), this operation affects only the client-side value; it has no effect upon a value stored in a database because JDBCConnection.createClob() constructs disconnected, initially empty Blob instances. To propagate the truncated Clob value to a database in this case, it is required to supply the Clob instance to an updating or inserting setXXX method of a Prepared or Callable Statement, or to supply the Blob instance to an updateXXX method of an updatable ResultSet.
Implementation Notes:
HSQLDB throws an SQLException if the specified len is greater
than the value returned by length.
truncate in interface Cloblen - the length, in characters, to which the CLOB value
should be truncated
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
public void free()
throws SQLException
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.
free in interface ClobSQLException - if an error occurs releasing
the Clob's resources
SQLFeatureNotSupportedException - if the JDBC driver does not support
this method
public Reader getCharacterStream(long pos,
long length)
throws SQLException
Reader object that contains a partial Clob value, starting
with the character specified by pos, which is length characters in length.
getCharacterStream in interface Clobpos - 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.
Reader through which the partial Clob value can be read.
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
|
||||||||||
| PREV CLASS NEXT CLASS | FRAMES NO FRAMES | |||||||||
| SUMMARY: NESTED | FIELD | CONSTR | METHOD | DETAIL: FIELD | CONSTR | METHOD | |||||||||