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java.lang.Objectorg.hsqldb.jdbc.JDBCBlob
public class JDBCBlob
The representation (mapping) in
the JavaTM programming
language of an SQL
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 is 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.
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.
| Field Summary | |
|---|---|
static long |
MAX_POS
|
static long |
MIN_POS
|
| Constructor Summary | |
|---|---|
JDBCBlob(byte[] data)
Constructs a new JDBCBlob instance wrapping the given octet sequence. |
|
| Method Summary | |
|---|---|
void |
free()
This method frees the Blob object and releases the resources that
it holds. |
InputStream |
getBinaryStream()
Retrieves the BLOB value designated by this
Blob instance as a stream. |
InputStream |
getBinaryStream(long pos,
long length)
Returns an InputStream object that contains a partial Blob 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 the BLOB
value that this Blob object represents, as an array of
bytes. |
long |
length()
Returns the number of bytes in the BLOB value
designated by this Blob object. |
long |
position(Blob pattern,
long start)
Retrieves the byte position in the BLOB value
designated by this Blob object at which
pattern begins. |
long |
position(byte[] pattern,
long start)
Retrieves the byte position at which the specified byte array pattern begins within the BLOB
value that this Blob object represents. |
OutputStream |
setBinaryStream(long pos)
Retrieves a stream that can be used to write to the BLOB
value that this Blob object represents. |
int |
setBytes(long pos,
byte[] bytes)
Writes the given array of bytes to the BLOB value that
this Blob object represents, starting at position
pos, and returns the number of bytes written. |
int |
setBytes(long pos,
byte[] bytes,
int offset,
int len)
Writes all or part of the given byte array to the
BLOB value that this Blob object represents
and returns the number of bytes written. |
void |
truncate(long len)
Truncates the BLOB value that this Blob
object represents to be len bytes in length. |
| Methods inherited from class java.lang.Object |
|---|
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
| Field Detail |
|---|
public static final long MIN_POS
public static final long MAX_POS
| Constructor Detail |
|---|
public JDBCBlob(byte[] data)
throws SQLException
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.
data - the octet sequence representing the Blob value
SQLException - if the argument is null| Method Detail |
|---|
public long length()
throws SQLException
BLOB value
designated by this Blob object.
length in interface BlobBLOB in bytes
SQLException - if there is an error accessing the
length of the BLOB
SQLFeatureNotSupportedException - if the JDBC driver does not support
this method
public byte[] getBytes(long pos,
int length)
throws SQLException
BLOB
value that this Blob object represents, as an array of
bytes. This byte array contains up to length
consecutive bytes starting at position pos.
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.
getBytes in interface Blobpos - the ordinal position of the first byte in the
BLOB 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]
length
consecutive bytes from the BLOB value designated
by this Blob object, starting with the
byte at position pos
SQLException - if there is an error accessing the
BLOB value; if pos is less than 1 or length is
less than 0
SQLFeatureNotSupportedException - if the JDBC driver does not support
this methodsetBytes(long, byte[])
public InputStream getBinaryStream()
throws SQLException
BLOB value designated by this
Blob instance as a stream.
getBinaryStream in interface BlobBLOB data
SQLException - if there is an error accessing the
BLOB value
SQLFeatureNotSupportedException - if the JDBC driver does not support
this methodsetBinaryStream(long)
public long position(byte[] pattern,
long start)
throws SQLException
pattern begins within the BLOB
value that this Blob object represents. The
search for pattern begins at position
start.
position in interface Blobpattern - the byte array for which to searchstart - the position at which to begin searching; the
first position is 1
SQLException - if there is an error accessing the
BLOB or if start is less than 1
SQLFeatureNotSupportedException - if the JDBC driver does not support
this method
public long position(Blob pattern,
long start)
throws SQLException
BLOB value
designated by this Blob object at which
pattern begins. The search begins at position
start.
position in interface Blobpattern - the Blob object designating
the BLOB value for which to searchstart - the position in the BLOB value
at which to begin searching; the first position is 1
SQLException - if there is an error accessing the
BLOB value or if start is less than 1
SQLFeatureNotSupportedException - if the JDBC driver does not support
this method
public int setBytes(long pos,
byte[] bytes)
throws SQLException
BLOB value that
this Blob object represents, starting at position
pos, and returns the number of bytes written.
The array of bytes will overwrite the existing bytes
in the Blob object starting at the position
pos. If the end of the Blob value is reached
while writing the array of bytes, then the length of the Blob
value will be increased to accommodate the extra bytes.
Note: If the value specified for pos
is greater then the length+1 of the BLOB 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 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 updateable 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.
setBytes in interface Blobpos - the position in the BLOB object at which
to start writing; the first position is 1bytes - the array of bytes to be written to the BLOB
value that this Blob object represents
SQLException - if there is an error accessing the
BLOB value or if pos is less than 1
SQLFeatureNotSupportedException - if the JDBC driver does not support
this methodgetBytes(long, int)
public int setBytes(long pos,
byte[] bytes,
int offset,
int len)
throws SQLException
byte array to the
BLOB value that this Blob object represents
and returns the number of bytes written.
Writing starts at position pos in the BLOB
value; len bytes from the given byte array are written.
The array of bytes will overwrite the existing bytes
in the Blob object starting at the position
pos. If the end of the Blob value is reached
while writing the array of bytes, then the length of the Blob
value will be increased to accommodate the extra bytes.
Note: If the value specified for pos
is greater then the length+1 of the BLOB 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 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 updateable ResultSet.
Implementation Notes:
If the value specified for pos
is greater than the length of the BLOB value, then
the BLOB value is extended in length to accept the
written octets and the undefined region up to pos 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.
setBytes in interface Blobpos - the position in the BLOB object at which
to start writing; the first position is 1bytes - the array of bytes to be written to this BLOB
objectoffset - the offset into the array bytes at which
to start reading the bytes to be setlen - the number of bytes to be written to the BLOB
value from the array of bytes bytes
SQLException - if there is an error accessing the
BLOB value or if pos is less than 1
SQLFeatureNotSupportedException - if the JDBC driver does not support
this methodgetBytes(long, int)
public OutputStream setBinaryStream(long pos)
throws SQLException
BLOB
value that this Blob object represents. The stream begins
at position pos.
The bytes written to the stream will overwrite the existing bytes
in the Blob object starting at the position
pos. If the end of the Blob value is reached
while writing to the stream, then the length of the Blob
value will be increased to accommodate the extra bytes.
Note: If the value specified for pos
is greater then the length+1 of the BLOB 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 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 updateable 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 the BLOB value, then
the BLOB value is extended in length to accept the
written octets and the undefined region up to pos 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.
setBinaryStream in interface Blobpos - the position in the BLOB value at which
to start writing; the first position is 1
java.io.OutputStream object to which data can
be written
SQLException - if there is an error accessing the
BLOB value or if pos is less than 1
SQLFeatureNotSupportedException - if the JDBC driver does not support
this methodgetBinaryStream()
public void truncate(long len)
throws SQLException
BLOB value that this Blob
object represents to be len bytes in length.
Note: If the value specified for pos
is greater then the length+1 of the BLOB 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 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.
truncate in interface Bloblen - the length, in bytes, to which the BLOB value
that this Blob object represents should be truncated
SQLException - if there is an error accessing the
BLOB value or if len is less than 0
SQLFeatureNotSupportedException - if the JDBC driver does not support
this method
public void free()
throws SQLException
Blob 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.
free in interface BlobSQLException - if an error occurs releasing
the Blob's resources
SQLFeatureNotSupportedException - if the JDBC driver does not support
this method
public InputStream getBinaryStream(long pos,
long length)
throws SQLException
InputStream object that contains a partial Blob value,
starting with the byte specified by pos, which is length bytes in length.
getBinaryStream in interface Blobpos - the offset to the first byte of the partial value to be retrieved.
The first byte in the Blob is at position 1length - the length in bytes of the partial value to be retrieved
InputStream through which the partial Blob value can be read.
SQLException - if pos is less than 1 or if pos is greater than the number of bytes
in the Blob or if pos + length is greater than the number of bytes
in the Blob
SQLFeatureNotSupportedException - if the JDBC driver does not support
this method
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