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 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 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

    Constructors
    Constructor
    Description
    JDBCBlob(byte[] data)
    Constructs a new JDBCBlob instance wrapping the given octet sequence.

  • Method Summary

    Modifier and Type
    Method
    Description
    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(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.
    long
    position(Blob pattern, long start)
    Retrieves the byte position in the BLOB value designated by this Blob object at which pattern begins.
    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 Object

    equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • 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 Details

    • 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; 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:

    • 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:

    • 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 than the length+1 of the BLOB value then the behavior is undefined. Some JDBC drivers may throw an 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 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 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:

    • 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 than the length+1 of the BLOB value then the behavior is undefined. Some JDBC drivers may throw an 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 updatable 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:

    • 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 than the length+1 of the BLOB value then the behavior is undefined. Some JDBC drivers may throw an 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 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 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:

    • 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 than the length+1 of the BLOB value then the behavior is undefined. Some JDBC drivers may throw an 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 an 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