Abstraction for handling large binary fields and large text fields in
specific databases, no matter if represented as simple types or Large OBjects.
Provides accessor methods for BLOBs and CLOBs, and acts as factory for
LobCreator instances, to be used as sessions for creating BLOBs or CLOBs.
LobCreators are typically instantiated for each statement execution or for
each transaction; they are not thread-safe because they might track
allocated database resources in order to free them after execution.
Most databases/drivers should be able to work with DefaultLobHandler,
which by default delegates to JDBC's direct accessor methods, avoiding the
java.sql.Blob and java.sql.Clob API completely.
DefaultLobHandler can also be configured to access LOBs using
PreparedStatement.setBlob/setClob (e.g. for PostgreSQL), through
setting the "wrapAsLob" property.
Of course, you need to declare different field types for each database.
In Oracle, any binary content needs to go into a BLOB, and all character content
beyond 4000 bytes needs to go into a CLOB. In MySQL, there is no notion of a
CLOB type but rather a LONGTEXT type that behaves like a VARCHAR. For complete
portability, use a LobHandler for fields that might typically require LOBs on
some database because of the field size (take Oracle's numbers as a guideline).
Summarizing the recommended options (for actual LOB fields):
JDBC 4.0 driver (including Oracle 11g driver): Use DefaultLobHandler,
potentially with streamAsLob=true if your database driver requires that
hint when populating a LOB field. Fall back to createTemporaryLob=true
if you happen to run into LOB size limitations with your (Oracle) database setup.
Oracle 10g driver: Use DefaultLobHandler with standard setup.
On Oracle 10.1, set the "SetBigStringTryClob" connection property; as of Oracle 10.2,
DefaultLobHandler should work with standard setup out of the box.
PostgreSQL: Configure DefaultLobHandler with wrapAsLob=true,
and use that LobHandler to access OID columns (but not BYTEA) in your database tables.
For all other database drivers (and for non-LOB fields that might potentially
turn into LOBs on some databases): Simply use a plain DefaultLobHandler.
Create a new LobCreator instance, i.e. a session for creating BLOBs
and CLOBs. Needs to be closed after the created LOBs are not needed anymore -
typically after statement execution or transaction completion.