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From "Laurenz Albe (JIRA)" <derby-...@db.apache.org>
Subject [jira] Created: (DERBY-463) Successive writes to a java.sql.Blob.setBinaryStream(long) seem to reset the file pointer
Date Fri, 15 Jul 2005 12:55:09 GMT
Successive writes to a java.sql.Blob.setBinaryStream(long) seem to reset the file pointer
-----------------------------------------------------------------------------------------

         Key: DERBY-463
         URL: http://issues.apache.org/jira/browse/DERBY-463
     Project: Derby
        Type: Bug
  Components: JDBC  
    Versions: 10.0.2.1    
 Environment: Sun java full version "1.4.2_05-b04"
Linux x86
Derby is run in network server mode
    Reporter: Laurenz Albe


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))) {
         outstream.write(buf, 0, count);
         System.out.println("Written " + count + " bytes to Blob");
      }

      // 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();
   }
}

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