Exception getting blob to byte[]

Question

Hy guys,
I 've a problem with my java application.
I use hibernate to interact with a derby database.
I stored a image into blob field (and no problem).
When I try to get blob to array of byte I've this exception:
java.sql.SQLException: You cannot invoke other java.sql.Clob/java.sql.Blob methods after calling the free() method or after the Blob/Clob's transaction has been committed or rolled back.To get blob I did
Blob cThumnb = ((Allegato) cAllegati.get(i)).getThumb();
byte[] cPrev = toByteArray(cThumnb);where
private byte[] toByteArray(Blob fromBlob) {
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        try {
            return toByteArrayImpl(fromBlob, baos);
        catch (SQLException e)
            throw new RuntimeException(e);
        catch (IOException e)
            throw new RuntimeException(e);
        finally
            if (baos != null)
                try
                    baos.close();
                catch (IOException ex)
    private byte[] toByteArrayImpl(Blob fromBlob, ByteArrayOutputStream baos)  throws SQLException, IOException
        byte[] buf = new byte[4000];
        InputStream is = fromBlob.getBinaryStream();
        try
            for (;;)
                int dataSize = is.read(buf);
                if (dataSize == -1)     break;
                baos.write(buf, 0, dataSize);
        catch(IOException ex)
                throw ex;
       finally
            if (is != null)
                try
                    is.close();
                catch (IOException ex)
                return  buf;// baos.toByteArray();
    }Could you help me?
I set also autocommit to false,
Thanks,
Regards

Answer 1

EJP wrote:
So could you cite some references that show, in general, that one normally needs to process blobs as streams?The design. The name, which is an acroynm for Binary Large Object. The fact that they have a stream interface, like files and sockets.The idiom for loading does not require nor even recommend that one must process as a stream.
And most of the time I do not process files nor sockets via streaming methodologies. I load them entirely, then process them.
Actually for direct socket usage, excluding protocols like FTP, I don't believe I have ever streamed processing because in message based protocols the messages are very small.
Presumably because the OP has one reference to 'thumb' as in thumbnail view?From the OP's first post: 'I stored a image into blob field'.I see. I have stored images in databases before. Excluding storage of medical media files they were all processed in memory because all were rather small.
Certainly cases where one does in fact want to read an entire file into memory, before one starts processing it.Can't think of any, but in any case if you are able to process it as a stream you are wasting both time and space by not doing so.If I have any data that is in fact "large" I will keep that in mind. But, for example, I can't see processing a configuration file that consists of a couple hundred bytes via stream processing just because files allow for the possibility that one can process a large file.