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java.sql.Blob and java.sql.Clob interfaces

<< Implementation notes on java.sql.Blob methods | JDBC 4.0 and 4.1 features >>

Derby Reference Manual

319

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.

Notes on mapping of java.sql.Blob and java.sql.Clob interfaces

The usual Derby locking mechanisms (shared locks) prevent other transactions from
updating or deleting the database item to which the java.sql.Blob or java.sql.Clob
object is a pointer. However, in some cases, Derby's instantaneous lock mechanisms
could allow a period of time in which the column underlying the java.sql.Blob
or java.sql.Clob is unprotected. A subsequent call to getBlob/getClob, or to a
java.sql.Blob/java.sql.Clobmethod, could cause undefined behavior.

Furthermore, there is nothing to prevent the transaction that holds the
java.sql.Blob/java.sql.Clob (as opposed to another transaction) from updating
the underlying row. (The same problem exists with the getXXXStream methods.)
Program applications to prevent updates to the underlying object while a
java.sql.Blob/java.sql.Clob is open on it; failing to do this could result in undefined
behavior.

Do not call more than one of the ResultSet getXXX methods on the same column if one
of the methods is one of the following:

· getBlob
· getClob
· getAsciiStream
· getBinaryStream
· getCharacterStream

These methods share the same underlying stream; calling more than one of these
methods on the same column could result in undefined behavior. For example:

ResultSet rs = s.executeQuery("SELECT text FROM CLOBS WHERE i = 1");
while (rs.next()) {
aclob = rs.getClob(1);
ip = rs.getAsciiStream(1);
}

The streams that handle long-columns are not thread safe. This means that if a user
chooses to open multiple threads and access the stream from each thread, the resulting
behavior is undefined.

Clobs are not locale-sensitive.

JDBC Package for Connected Device Configuration/Foundation
Profile (JSR 169)

Derby supports the JDBC API defined for the Connected Device
Configuration/Foundation Profile, also known as JSR 169. The features supported are