- All Implemented Interfaces:
Blob
BLOB
value. An SQL BLOB
is a built-in type
that stores a Binary Large Object as a column value in a row of
a database table. By default drivers implement Blob
using
an SQL locator(BLOB)
, which means that a
Blob
object contains a logical pointer to the
SQL BLOB
data rather than the data itself.
A Blob
object is valid for the duration of the
transaction in which it was created.
Methods in the interfaces ResultSet
,
CallableStatement
, and PreparedStatement
, such as
getBlob
and setBlob
allow a programmer to
access an SQL BLOB
value.
The Blob
interface provides methods for getting the
length of an SQL BLOB
(Binary Large Object) value,
for materializing a BLOB
value on the client, and for
determining the position of a pattern of bytes within a
BLOB
value. In addition, this interface has methods for updating
a BLOB
value.
All methods on the Blob
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 Blob using an SQL locator(BLOB). That is, an HSQLDB Blob object did not contain a logical pointer to SQL BLOB data; rather it directly contained a representation of the data (a byte array). As a result, an HSQLDB Blob 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 BLOB 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 BLOB data implementations, meaning that an HSQLDB Blob object may
contain a logical pointer to remote SQL BLOB data (see JDBCBlobClient
) 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 Blob instance is constructed as a result of calling
JDBCConnection.createBlob(), then the resulting Blob 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 BLOB value are supported for local use until the first
invocation of free(); otherwise, an HSQLDB Blob'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:
- james house (jhouse@part.net), Campbell Burnet (campbell-burnet@users dot sourceforge.net)
-
Constructor Summary
ConstructorsConstructorDescriptionJDBCBlob
(byte[] data) Constructs a new JDBCBlob instance wrapping the given octet sequence. -
Method Summary
Modifier and TypeMethodDescriptionvoid
free()
This method frees theBlob
object and releases the resources that it holds.Retrieves theBLOB
value designated by thisBlob
instance as a stream.getBinaryStream
(long pos, long length) Returns anInputStream
object that contains a partialBlob
value, starting with the byte specified by pos, which is length bytes in length.byte[]
getBytes
(long pos, int length) Retrieves all or part of theBLOB
value that thisBlob
object represents, as an array of bytes.long
length()
Returns the number of bytes in theBLOB
value designated by thisBlob
object.long
position
(byte[] pattern, long start) Retrieves the byte position at which the specified byte arraypattern
begins within theBLOB
value that thisBlob
object represents.long
Retrieves the byte position in theBLOB
value designated by thisBlob
object at whichpattern
begins.setBinaryStream
(long pos) Retrieves a stream that can be used to write to theBLOB
value that thisBlob
object represents.int
setBytes
(long pos, byte[] bytes) Writes the given array of bytes to theBLOB
value that thisBlob
object represents, starting at positionpos
, and returns the number of bytes written.int
setBytes
(long pos, byte[] bytes, int offset, int len) Writes all or part of the givenbyte
array to theBLOB
value that thisBlob
object represents and returns the number of bytes written.void
truncate
(long len) Truncates theBLOB
value that thisBlob
object represents to belen
bytes in length.
-
Constructor Details
-
JDBCBlob
Constructs a new JDBCBlob instance wrapping the given octet sequence.This constructor is used internally to retrieve result set values as Blob 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 octet sequence rather than making a copy; special care should be taken by external clients never to use this constructor with a byte array object that may later be modified externally.
- Parameters:
data
- the octet sequence representing the Blob value- Throws:
SQLException
- if the argument is null
-
-
Method Details
-
length
Returns the number of bytes in theBLOB
value designated by thisBlob
object.- Specified by:
length
in interfaceBlob
- Returns:
- length of the
BLOB
in bytes - Throws:
SQLException
- if there is an error accessing the length of theBLOB
SQLFeatureNotSupportedException
- if the JDBC driver does not support this method- Since:
- JDK 1.2, HSQLDB 1.7.2
-
getBytes
Retrieves all or part of theBLOB
value that thisBlob
object represents, as an array of bytes. Thisbyte
array contains up tolength
consecutive bytes starting at positionpos
.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 octets from pos to this.length(). Another would be to throw an exception. HSQLDB observes the second policy.- Specified by:
getBytes
in interfaceBlob
- Parameters:
pos
- the ordinal position of the first byte in theBLOB
value to be extracted; the first byte is at position 1length
- the number of consecutive bytes to be copied; JDBC 4.1[the value for length must be 0 or greater]- Returns:
- a byte array containing up to
length
consecutive bytes from theBLOB
value designated by thisBlob
object, starting with the byte at positionpos
- Throws:
SQLException
- if there is an error accessing theBLOB
value; if pos is less than 1 or length is less than 0SQLFeatureNotSupportedException
- if the JDBC driver does not support this method- Since:
- JDK 1.2, HSQLDB 1.7.2
- See Also:
-
getBinaryStream
Retrieves theBLOB
value designated by thisBlob
instance as a stream.- Specified by:
getBinaryStream
in interfaceBlob
- Returns:
- a stream containing the
BLOB
data - Throws:
SQLException
- if there is an error accessing theBLOB
valueSQLFeatureNotSupportedException
- if the JDBC driver does not support this method- Since:
- JDK 1.2, HSQLDB 1.7.2
- See Also:
-
position
Retrieves the byte position at which the specified byte arraypattern
begins within theBLOB
value that thisBlob
object represents. The search forpattern
begins at positionstart
.- Specified by:
position
in interfaceBlob
- Parameters:
pattern
- the byte array for which to searchstart
- the position at which to begin searching; the first position is 1- Returns:
- the position at which the pattern appears, else -1
- Throws:
SQLException
- if there is an error accessing theBLOB
or if start is less than 1SQLFeatureNotSupportedException
- if the JDBC driver does not support this method- Since:
- JDK 1.2, HSQLDB 1.7.2
-
position
Retrieves the byte position in theBLOB
value designated by thisBlob
object at whichpattern
begins. The search begins at positionstart
.- Specified by:
position
in interfaceBlob
- Parameters:
pattern
- theBlob
object designating theBLOB
value for which to searchstart
- the position in theBLOB
value at which to begin searching; the first position is 1- Returns:
- the position at which the pattern begins, else -1
- Throws:
SQLException
- if there is an error accessing theBLOB
value or if start is less than 1SQLFeatureNotSupportedException
- if the JDBC driver does not support this method- Since:
- JDK 1.2, HSQLDB 1.7.2
-
setBytes
Writes the given array of bytes to theBLOB
value that thisBlob
object represents, starting at positionpos
, and returns the number of bytes written. The array of bytes will overwrite the existing bytes in theBlob
object starting at the positionpos
. If the end of theBlob
value is reached while writing the array of bytes, then the length of theBlob
value will be increased to accommodate the extra bytes.Note: If the value specified for
pos
is greater than the length+1 of theBLOB
value then the behavior is undefined. Some JDBC drivers may throw aSQLException
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 Blob instance is constructed as a result of calling JDBCConnection.createBlob(), this operation affects only the client-side value; it has no effect upon a value stored in a database because JDBCConnection.createBlob() constructs disconnected, initially empty Blob instances. To propagate the Blob value to a database in this case, it is required to supply the Blob 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:
Starting with HSQLDB 2.1, JDBCBlob no longer utilizes volatile fields and is effectively thread safe, but still uses local variable snapshot isolation.
As such, the synchronization policy still does not strictly enforce serialized read/write access to the underlying data
So, if an application may perform concurrent JDBCBlob modifications and the integrity of the application depends on total order Blob modification semantics, then such operations should be synchronized on an appropriate monitor.
- Specified by:
setBytes
in interfaceBlob
- Parameters:
pos
- the position in theBLOB
object at which to start writing; the first position is 1bytes
- the array of bytes to be written to theBLOB
value that thisBlob
object represents- Returns:
- the number of bytes written
- Throws:
SQLException
- if there is an error accessing theBLOB
value or if pos is less than 1SQLFeatureNotSupportedException
- if the JDBC driver does not support this method- Since:
- JDK 1.4, HSQLDB 1.7.2
- See Also:
-
setBytes
Writes all or part of the givenbyte
array to theBLOB
value that thisBlob
object represents and returns the number of bytes written. Writing starts at positionpos
in theBLOB
value;len
bytes from the given byte array are written. The array of bytes will overwrite the existing bytes in theBlob
object starting at the positionpos
. If the end of theBlob
value is reached while writing the array of bytes, then the length of theBlob
value will be increased to accommodate the extra bytes.Note: If the value specified for
pos
is greater than the length+1 of theBLOB
value then the behavior is undefined. Some JDBC drivers may throw aSQLException
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 Blob instance is constructed as a result of calling JDBCConnection.createBlob(), this operation affects only the client-side value; it has no effect upon a value stored in a database because JDBCConnection.createBlob() constructs disconnected, initially empty Blob instances. To propagate the Blob value to a database in this case, it is required to supply the Blob 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:
If the value specified for
pos
is greater than the length of theBLOB
value, then theBLOB
value is extended in length to accept the written octets and the undefined region up topos
is filled with (byte)0.Starting with HSQLDB 2.1, JDBCBlob no longer utilizes volatile fields and is effectively thread safe, but still uses local variable snapshot isolation.
As such, the synchronization policy still does not strictly enforce serialized read/write access to the underlying data
So, if an application may perform concurrent JDBCBlob modifications and the integrity of the application depends on total order Blob modification semantics, then such operations should be synchronized on an appropriate monitor.
- Specified by:
setBytes
in interfaceBlob
- Parameters:
pos
- the position in theBLOB
object at which to start writing; the first position is 1bytes
- the array of bytes to be written to thisBLOB
objectoffset
- the offset into the arraybytes
at which to start reading the bytes to be setlen
- the number of bytes to be written to theBLOB
value from the array of bytesbytes
- Returns:
- the number of bytes written
- Throws:
SQLException
- if there is an error accessing theBLOB
value or if pos is less than 1SQLFeatureNotSupportedException
- if the JDBC driver does not support this method- Since:
- JDK 1.4, HSQLDB 1.7.2
- See Also:
-
setBinaryStream
Retrieves a stream that can be used to write to theBLOB
value that thisBlob
object represents. The stream begins at positionpos
. The bytes written to the stream will overwrite the existing bytes in theBlob
object starting at the positionpos
. If the end of theBlob
value is reached while writing to the stream, then the length of theBlob
value will be increased to accommodate the extra bytes.Note: If the value specified for
pos
is greater than the length+1 of theBLOB
value then the behavior is undefined. Some JDBC drivers may throw aSQLException
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 Blob instance is constructed as a result of calling JDBCConnection.createBlob(), this operation affects only the client-side value; it has no effect upon a value stored in a database because JDBCConnection.createBlob() constructs disconnected, initially empty Blob instances. To propagate the Blob value to a database in this case, it is required to supply the Blob 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:
The data written to the stream does not appear in this Blob until the stream is closed
When the stream is closed, if the value specified for
pos
is greater than the length of theBLOB
value, then theBLOB
value is extended in length to accept the written octets and the undefined region up topos
is filled with (byte)0.Starting with HSQLDB 2.1, JDBCBlob no longer utilizes volatile fields and is effectively thread safe, but still uses local variable snapshot isolation.
As such, the synchronization policy still does not strictly enforce serialized read/write access to the underlying data
So, if an application may perform concurrent JDBCBlob modifications and the integrity of the application depends on total order Blob modification semantics, then such operations should be synchronized on an appropriate monitor.
- Specified by:
setBinaryStream
in interfaceBlob
- Parameters:
pos
- the position in theBLOB
value at which to start writing; the first position is 1- Returns:
- a
java.io.OutputStream
object to which data can be written - Throws:
SQLException
- if there is an error accessing theBLOB
value or if pos is less than 1SQLFeatureNotSupportedException
- if the JDBC driver does not support this method- Since:
- JDK 1.4, HSQLDB 1.7.2
- See Also:
-
truncate
Truncates theBLOB
value that thisBlob
object represents to belen
bytes in length.Note: If the value specified for
pos
is greater than the length+1 of theBLOB
value then the behavior is undefined. Some JDBC drivers may throw aSQLException
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 Blob instance is constructed as a result of calling JDBCConnection.createBlob(), this operation affects only the client-side value; it has no effect upon a value stored in a database because JDBCConnection.createBlob() constructs disconnected, initially empty Blob instances. To propagate the truncated Blob value to a database in this case, it is required to supply the Blob 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.
- Specified by:
truncate
in interfaceBlob
- Parameters:
len
- the length, in bytes, to which theBLOB
value that thisBlob
object represents should be truncated- Throws:
SQLException
- if there is an error accessing theBLOB
value or if len is less than 0SQLFeatureNotSupportedException
- if the JDBC driver does not support this method- Since:
- JDK 1.4, HSQLDB 1.7.2
-
free
This method frees theBlob
object and releases the resources that it holds. The object is invalid once thefree
method is called.After
free
has been called, any attempt to invoke a method other thanfree
will result in aSQLException
being thrown. Iffree
is called multiple times, the subsequent calls tofree
are treated as a no-op.- Specified by:
free
in interfaceBlob
- Throws:
SQLException
- if an error occurs releasing the Blob's resourcesSQLFeatureNotSupportedException
- if the JDBC driver does not support this method- Since:
- JDK 1.6, HSQLDB 2.0
-
getBinaryStream
Returns anInputStream
object that contains a partialBlob
value, starting with the byte specified by pos, which is length bytes in length.- Specified by:
getBinaryStream
in interfaceBlob
- Parameters:
pos
- the offset to the first byte of the partial value to be retrieved. The first byte in theBlob
is at position 1length
- the length in bytes of the partial value to be retrieved- Returns:
InputStream
through which the partialBlob
value can be read.- Throws:
SQLException
- if pos is less than 1 or if pos is greater than the number of bytes in theBlob
or if pos + length is greater than the number of bytes in theBlob
SQLFeatureNotSupportedException
- if the JDBC driver does not support this method- Since:
- JDK 1.6, HSQLDB 2.0
-