In the JDBC API, java.sql.Blob is the mapping for the SQL BLOB (binary large object) type; java.sql.Clob is the mapping for the SQL CLOB (character large object) type. BLOB and CLOB objects are collectively referred to as LOBs (large objects).
The Derby implementation of the java.sql.Blob and java.sql.Clob interfaces is LOCATOR-based, meaning that the implementation provides a logical pointer to a LOB rather than a complete copy of the object. Also, Derby does not materialize a LOB when you use the BLOB or CLOB data type. You can, however, call methods on a java.sql.Blob and java.sql.Clob object to materialize it (that is, to retrieve the entire object or parts of it).
Derby implements all of the methods for these interfaces except for the setBlob, getBlob, setClob, and getClob methods of the CallableStatement interface.
Casting between strings and BLOBs is not recommended because casting is platform- and database-dependent.
As with other character datatypes, Derby treats CLOBs as unicode strings and writes them to disk using UTF8 encoding. With a Java database like Derby, you do not need to worry about character sets and codepages.
Recommendation: Because the lifespan of a java.sql.Blob or java.sql.Clob ends when the transaction commits, turn off auto-commit with the java.sql.Blob or java.sql.Clob features.
Returns | Signature | Implementation Notes |
---|---|---|
byte[] | getBytes(long pos, int length) | Exceptions are raised if pos < 1, if pos is larger than the length of the , or if length <= 0. |
long | position(byte[] pattern, long start) | Exceptions are raised if pattern == null, if start < 1, or if pattern is an array of length 0. |
long | position(Blob pattern, long start) | Exceptions are raised if pattern == null, if start < 1, if pattern has length 0, or if an exception is thrown when trying to read the first byte of pattern. |
Returns | Signature | Implementation Notes |
---|---|---|
String | getSubString(long pos, int length) | Exceptions are raised if pos < 1, if pos is larger than the length of the Clob, or if length <= 0. |
long | position(Clob searchstr, long start) | Exceptions are raised if searchStr == null or start < 1, if searchStr has length 0, or if an exception is thrown when trying to read the first char of searchStr. |
long | position(String searchstr, long start) | Exceptions are raised if searchStr == null or start < 1, or if the pattern is an empty string. |