org.hsqldb.jdbc
Class JDBCBlob

java.lang.Object
  org.hsqldb.jdbc.JDBCBlob

All Implemented Interfaces:

Blob

public class JDBCBlob
extends Object
implements Blob

The representation (mapping) in the Java^TM 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.

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, boucherb@users

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

MIN_POS

public static final long MIN_POS

See Also:

Constant Field Values

MAX_POS

public static final long MAX_POS

See Also:

Constant Field Values

Constructor Detail

JDBCBlob

public JDBCBlob(byte[] data)
         throws SQLException

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 Detail

length

public long length()
            throws SQLException

Returns the number of bytes in the BLOB value designated by this Blob object.

Specified by:

length in interface Blob

Returns:

length of the BLOB in bytes

Throws:

SQLException - if there is an error accessing the length of the BLOB

SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.2, HSQLDB 1.7.2

getBytes

public byte[] getBytes(long pos,
                       int length)
                throws SQLException

Retrieves all or part of the 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.

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 interface Blob

Parameters:

pos - the ordinal position of the first byte in the BLOB value to be extracted; the first byte is at position 1

length - 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 the BLOB value designated by this Blob object, starting with the byte at position pos

Throws:

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 method

Since:

JDK 1.2, HSQLDB 1.7.2

See Also:

setBytes(long, byte[])

getBinaryStream

public InputStream getBinaryStream()
                            throws SQLException

Retrieves the BLOB value designated by this Blob instance as a stream.

Specified by:

getBinaryStream in interface Blob

Returns:

a stream containing the BLOB data

Throws:

SQLException - if there is an error accessing the BLOB value

SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.2, HSQLDB 1.7.2

See Also:

setBinaryStream(long)

position

public long position(byte[] pattern,
                     long start)
              throws SQLException

Retrieves the byte position at which the specified byte array pattern begins within the BLOB value that this Blob object represents. The search for pattern begins at position start.

Specified by:

position in interface Blob

Parameters:

pattern - the byte array for which to search

start - 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 the BLOB or if start is less than 1

SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.2, HSQLDB 1.7.2

position

public long position(Blob pattern,
                     long start)
              throws SQLException

Retrieves the byte position in the BLOB value designated by this Blob object at which pattern begins. The search begins at position start.

Specified by:

position in interface Blob

Parameters:

pattern - the Blob object designating the BLOB value for which to search

start - the position in the BLOB 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 the BLOB value or if start is less than 1

SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.2, HSQLDB 1.7.2

setBytes

public int setBytes(long pos,
                    byte[] bytes)
             throws SQLException

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. 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.

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 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.

Specified by:

setBytes in interface Blob

Parameters:

pos - the position in the BLOB object at which to start writing; the first position is 1

bytes - the array of bytes to be written to the BLOB value that this Blob object represents

Returns:

the number of bytes written

Throws:

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 method

Since:

JDK 1.4, HSQLDB 1.7.2

See Also:

getBytes(long, int)

setBytes

public int setBytes(long pos,
                    byte[] bytes,
                    int offset,
                    int len)
             throws SQLException

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. 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.

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 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.

Specified by:

setBytes in interface Blob

Parameters:

pos - the position in the BLOB object at which to start writing; the first position is 1

bytes - the array of bytes to be written to this BLOB object

offset - the offset into the array bytes at which to start reading the bytes to be set

len - the number of bytes to be written to the BLOB value from the array of bytes bytes

Returns:

the number of bytes written

Throws:

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 method

Since:

JDK 1.4, HSQLDB 1.7.2

See Also:

getBytes(long, int)

setBinaryStream

public OutputStream setBinaryStream(long pos)
                             throws SQLException

Retrieves a stream that can be used to write to the 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.

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 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.

Specified by:

setBinaryStream in interface Blob

Parameters:

pos - the position in the BLOB 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 the BLOB value or if pos is less than 1

SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.4, HSQLDB 1.7.2

See Also:

getBinaryStream()

truncate

public void truncate(long len)
              throws SQLException

Truncates the 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.

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 interface Blob

Parameters:

len - the length, in bytes, to which the BLOB value that this Blob object represents should be truncated

Throws:

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

Since:

JDK 1.4, HSQLDB 1.7.2

free

public void free()
          throws SQLException

This method frees the 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.

Specified by:

free in interface Blob

Throws:

SQLException - if an error occurs releasing the Blob's resources

SQLFeatureNotSupportedException - if the JDBC driver does not support this method

Since:

JDK 1.6, HSQLDB 2.0

getBinaryStream

public InputStream getBinaryStream(long pos,
                                   long length)
                            throws SQLException

Returns an InputStream object that contains a partial Blob value, starting with the byte specified by pos, which is length bytes in length.

Specified by:

getBinaryStream in interface Blob

Parameters:

pos - the offset to the first byte of the partial value to be retrieved. The first byte in the Blob is at position 1

length - the length in bytes of the partial value to be retrieved

Returns:

InputStream through which the partial Blob value can be read.

Throws:

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

Since:

JDK 1.6, HSQLDB 2.0