Module org.hsqldb

Package org.hsqldb.jdbc

Class JDBCClob

java.lang.Object

org.hsqldb.jdbc.JDBCClob

All Implemented Interfaces:

java.sql.Clob

Direct Known Subclasses:

JDBCNClob

public class JDBCClob
extends java.lang.Object
implements java.sql.Clob

The mapping in the Java™ 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.

HSQLDB-Specific Information:

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.

Since:

JDK 1.2, HSQLDB 1.7.2

Author:

Campbell Burnet (campbell-burnet@users dot sourceforge.net)

Constructor Summary

Constructors

Constructor	Description
JDBCClob(java.lang.String data)	Constructs a new, read-only JDBCClob object wrapping the given character sequence.

Method Summary

Modifier and Type	Method	Description
void	free()	This method frees the Clob object and releases the resources that it holds.
java.io.InputStream	getAsciiStream()	Retrieves the CLOB value designated by this Clob object as an ASCII stream.
java.io.Reader	getCharacterStream()	Retrieves the CLOB value designated by this Clob object as a java.io.Reader object (or 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.
java.lang.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(java.lang.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.
long	position(java.sql.Clob searchstr, long start)	Retrieves the character position at which the specified Clob object searchstr appears in this Clob object.
java.io.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.
java.io.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, java.lang.String str)	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)	Writes len characters of str, starting at character offset, to the CLOB value that this Clob represents.
int	setStringBuffer(long pos, java.lang.StringBuffer sb, int offset, int len)	Behaviour is identical to setString(long, java.lang.String, int, int).
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

JDBCClob

public JDBCClob(java.lang.String data)
         throws java.sql.SQLException

Constructs a new, read-only JDBCClob object wrapping the given character sequence.

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.

Parameters:

data - the character sequence representing the Clob value

Throws:

java.sql.SQLException - if the argument is null

Method Detail

length

public long length()
            throws java.sql.SQLException

Retrieves the number of characters in the CLOB value designated by this Clob object.

Specified by:

length in interface java.sql.Clob

Returns:

length of the CLOB in characters

Throws:

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

java.sql.SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.2, HSQLDB 1.7.2

getSubString

public java.lang.String getSubString(long pos,
                                     int length)
                              throws java.sql.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.

HSQLDB-Specific Information:

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. This class observes the second policy.

Note

This method uses String.substring(int, int).

Depending on implementation (typically JDK 6 and earlier releases), the returned value may be sharing the underlying (and possibly much larger) character buffer. Depending on factors such as hardware acceleration for array copies, the average length and number of sub-strings taken, and so on, this may or may not result in faster operation and non-trivial memory savings. On the other hand, Oracle / OpenJDK 7, it was decided that the memory leak implications outweigh the benefits of buffer sharing for most use cases on modern hardware.

It is left up to any client of this method to determine if this is a potential factor relative to the target runtime and to decide how to handle space-time trade-offs (i.e. whether to make an isolated copy of the returned substring or risk that more memory remains allocated than is absolutely required).

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; JDBC 4.1[ 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:

java.sql.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]

java.sql.SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.2, HSQLDB 1.7.2

getCharacterStream

public java.io.Reader getCharacterStream()
                                  throws java.sql.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 java.sql.Clob

Returns:

a java.io.Reader object containing the CLOB data

Throws:

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

java.sql.SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.2, HSQLDB 1.7.2

See Also:

setCharacterStream(long)

getAsciiStream

public java.io.InputStream getAsciiStream()
                                   throws java.sql.SQLException

Retrieves the CLOB value designated by this Clob object as an ASCII stream.

Specified by:

getAsciiStream in interface java.sql.Clob

Returns:

a java.io.InputStream object containing the CLOB data

Throws:

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

java.sql.SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.2, HSQLDB 1.7.2

See Also:

setAsciiStream(long)

position

public long position(java.lang.String searchstr,
                     long start)
              throws java.sql.SQLException

Retrieves the character position at which the specified substring searchstr appears in the SQL CLOB value represented by this Clob object. The search begins at position start.

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 or -1 if it is not present; the first position is 1

Throws:

java.sql.SQLException - if there is an error accessing the CLOB value or if start is less than 1

java.sql.SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.2, HSQLDB 1.7.2

position

public long position(java.sql.Clob searchstr,
                     long start)
              throws java.sql.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 java.sql.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:

java.sql.SQLException - if there is an error accessing the CLOB value or if start is less than 1

java.sql.SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.2, HSQLDB 1.7.2

setString

public int setString(long pos,
                     java.lang.String str)
              throws java.sql.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 than 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.

HSQLDB-Specific Information:

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 updateable 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, 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.

When the value specified for pos is greater then the length+1, then the CLOB value is extended in length to accept the written characters and the undefined region up to @{code pos} is filled with with space (' ') characters.

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; 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:

java.sql.SQLException - if there is an error accessing the CLOB value or if pos is less than 1

java.sql.SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.4, HSQLDB 1.7.2

setString

public int setString(long pos,
                     java.lang.String str,
                     int offset,
                     int len)
              throws java.sql.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 than 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.

HSQLDB-Specific Information:

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 updateable 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 space (' ') characters.

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, 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.

Specified by:

setString in interface java.sql.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:

java.sql.SQLException - if there is an error accessing the CLOB value or if pos is less than 1

java.sql.SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.4, HSQLDB 1.7.2

setAsciiStream

public java.io.OutputStream setAsciiStream(long pos)
                                    throws java.sql.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 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.

HSQLDB-Specific Information:

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 space (' ') characters.

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, 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.

Specified by:

setAsciiStream in interface java.sql.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:

java.sql.SQLException - if there is an error accessing the CLOB value or if pos is less than 1

java.sql.SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.4, HSQLDB 1.7.2

See Also:

getAsciiStream()

setCharacterStream

public java.io.Writer setCharacterStream(long pos)
                                  throws java.sql.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 than 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.

HSQLDB-Specific Information:

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 updateable 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 space (' ') characters.

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, 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.

Specified by:

setCharacterStream in interface java.sql.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:

java.sql.SQLException - if there is an error accessing the CLOB value or if pos is less than 1

java.sql.SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.4, HSQLDB 1.7.2

See Also:

getCharacterStream()

truncate

public void truncate(long len)
              throws java.sql.SQLException

Truncates the 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.

HSQLDB-Specific Information:

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 updateable ResultSet.

Implementation Notes:

HSQLDB throws an SQLException if the specified len is greater than the value returned by length.

Specified by:

truncate in interface java.sql.Clob

Parameters:

len - the length, in characters, to which the CLOB value should be truncated

Throws:

java.sql.SQLException - if there is an error accessing the CLOB value or if len is less than 0

java.sql.SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.4, HSQLDB 1.7.2

free

public void free()
          throws java.sql.SQLException

This method frees the Clob object and releases 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 java.sql.Clob

Throws:

java.sql.SQLException - if an error occurs releasing the Clob's resources

java.sql.SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.6, HSQLDB 2.0

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 the number of characters in the Clob

java.sql.SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.6, HSQLDB 2.0

setStringBuffer

public int setStringBuffer(long pos,
                           java.lang.StringBuffer sb,
                           int offset,
                           int len)
                    throws java.sql.SQLException

Behaviour is identical to setString(long, java.lang.String, int, int).

Parameters:

pos - the position at which to start writing to this CLOB object; The first position is 1

sb - the buffer to be written to the CLOB value that this Clob object represents

offset - the offset into sb 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 there is an error accessing the CLOB value or if pos is less than 1