BLOBs and CLOBs
As users began to increase the volume of data stored in databases, vendors introduced support for large objects (LOBs). The two varieties of LOBs, binary large objects (BLOBs) and character large objects (CLOBs), store large amounts of binary or character data, respectively. The SQL99 specification formally defined these data types.
Support for LOB types across databases varies. Some don’t
support them at all, and most have unique type names (BINARY
, LONG RAW
, and so forth). JDBC 1.0 makes programs retrieve
BLOB
and CLOB
data using the getBinaryStream()
or getAsciiStream()
methods. (A third method,
getUnicodeStream()
, has been
deprecated in favor of the getCharacterStream()
method, which returns a
Reader
.)
As of JDBC 2.0, the ResultSet
interface includes getBlob()
and
getClob()
methods, which return
Blob
and Clob
objects, respectively. The Blob
and Clob
objects themselves allow access to
their data via streams (the getBinaryStream()
method of Blob
and the getCharacterStream()
method of Clob
) or via direct-read methods (
the getBytes()
method of Blob
and the getSubString()
method of Clob
).
To retrieve the data from a CLOB, simply retrieve the Clob
object and call the getCharacterStream()
method:
String s; Clob clob = blobResultSet.getBlob("CLOBFIELD"); BufferedReader clobData = new BufferedReader(clob.getCharacterStream()); while((s = clobData.readLine()) != null) System.out.println(s);
In addition, you can set Blob
and Clob
objects when you are working with a ...
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