Details
Major Description
I have a table
PEOPLE(SEQ_ID INT NOT NULL PRIMARY KEY, PICTURE BLOB).
A row is inserted; both values are not NULL.
From inside a JDBC program, I select the Blob for update.
I then get the Blob output stream with a call to
Blob.setBinaryStream(long)
To this stream I write several times with
OutputStream.write(byte[], int, int)
I close the stream, update the selected row with the new Blob and commit.
The new value of the Blob now is exactly the value of the last content of the byte[],
and it is like the previous calls to write() have never taken place, or as if the file pointer
of the output stream has been reset between the calls.
A sample program follows; the size of the input file "picture.jpg" is 23237, the length
of the Blob after the program has run is 23237 % 1024 = 709
------------ sample program -------------
import java.sql.*;
class TestApp {
private TestApp() {}
public static void main(String[] args)
throws ClassNotFoundException, SQLException, java.io.IOException {
// try to load JDBC driver
Class.forName("com.ibm.db2.jcc.DB2Driver");
// open the input file
java.io.InputStream instream = new java.io.FileInputStream("picture.jpg");
// login to database
Connection conn = DriverManager.getConnection(
"jdbc:derby:net://dbtuxe/testdb", "laurenz", "apassword");
conn.setAutoCommit(false);
// select Blob for update
PreparedStatement stmt = conn.prepareStatement(
"SELECT PICTURE FROM PEOPLE WHERE SEQ_ID=? FOR UPDATE OF PICTURE");
stmt.setInt(1, 1);
ResultSet rs = stmt.executeQuery();
// get Blob output stream
rs.next();
Blob blob = rs.getBlob(1);
java.io.OutputStream outstream = blob.setBinaryStream(1l);
// copy the input file to the Blob in chunks of 1K
byte[] buf = new byte[1024];
int count;
while (-1 != (count = instream.read(buf)))
// close streams
instream.close();
outstream.close();
// update Blob with new value
String cursor = rs.getCursorName();
PreparedStatement stmt2 = conn.prepareStatement(
"UPDATE PEOPLE SET PICTURE=? WHERE CURRENT OF " + cursor);
stmt2.setBlob(1, blob);
stmt2.executeUpdate();
// clean up
stmt2.close();
stmt.close();
conn.commit();
conn.close();
}
}