Oracle Extensions for LOBs and BFILEs

LOBs ("large objects") are stored in a way that optimizes space and provides efficient access. The JDBC drivers provide support for two types of LOBs: BLOBs (unstructured binary data) and CLOBs (character data). BLOB and CLOB data is accessed and referenced by using a locator, which is stored in the database table and points to the BLOB or CLOB data, which is outside the table.

BFILEs are large binary data objects stored in operating system files outside of database tablespaces. These files use reference semantics. They can also be located on tertiary storage devices such as hard disks, CD-ROMs, PhotoCDs and DVDs. As with BLOBs and CLOBs, a BFILE is accessed and referenced by a locator which is stored in the database table and points to the BFILE data.

To work with LOB data, you must first obtain the LOB locator from the table. Then you can read or write LOB data and perform data manipulation. The following sections also describe how to create and populate a LOB column in a table.

The JDBC drivers support these oracle.sql.* classes for BLOBs, CLOBs, and BFILEs:

• oracle.sql.BLOB

• oracle.sql.CLOB

• oracle.sql.BFILE

The oracle.sql.BLOB and CLOB classes implement the java.sql.Blob and Clob interfaces, respectively (oracle.jdbc2.Blob and Clob interfaces under JDK 1.1.x). By contrast, BFILE is an Oracle extension, without a corresponding java.sql (or oracle.jdbc2) interface.

Instances of these classes contain only the locators for these datatypes, not the data. After accessing the locators, you must perform some additional steps to access the data. These steps are described in "Reading and Writing BLOB and CLOB Data" and "Reading BFILE Data".

Note: You cannot create BLOB, CLOB, or BFILE objects in your JDBC application--you can only retrieve existing BLOBs, CLOBs, or BFILEs from the database.

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