Servlet on gae delevering a jpeg image

I wish to write a servlet to run in GAE . This servlet wants to upload a image and to send it to a email address . This is the code :

ServletFileUpload upload = new ServletFileUpload();
FileItemIterator iterator = upload.getItemIterator(request);
while (iterator.hasNext()) {
            FileItemStream itemStream = iterator.next();
            is = itemStream.openStream();
            if (itemStream.isFormField()){
                         String fieldname = itemStream.getFieldName();
                         if (fieldname.equals("Destinatar")){
                                         destination = Streams.asString(is);
                     }; 
                     if (fieldname.equals("Mesaj"))   {
                                     message = Streams.asString(is);
                     };
                     if (fieldname.equals("Subject"))   {
                                        Subject = Streams.asString(is);
                         };
                     } else {
                        filename = FilenameUtils.ge开发者_如何转开发tName(itemStream.getName());
                        contentFile = Streams.asString(is);
                     }
       }
..........
............
...........
MimeBodyPart attachment = new MimeBodyPart();
attachment.setFileName(filename);
ds = new ByteArrayDataSource(contentFile.getBytes() , "image/jpeg"); 
attachment.setDataHandler(new DataHandler(ds));
multipart.addBodyPart(attachment);
..............

Destination mailbox receives jpeg image -filename and dimension is right , like on the client- but browser can not understand the content ,it not recognize like a jpeg image. Do you have any ideea what's the problem? Thanks, Aurel

You are transforming a stream of binary data into a String at the line

contentFile = Streams.asString(is);

Don't do this. This transformation uses a charset and decodes bytes into chars, but certainly fails because the stream doesn't hold valid characters of this charset. If it's binary, store it as binary (into a stream, or a byte array) :

InputStream fileContent;
// ...
    else {
        filename = FilenameUtils.getName(itemStream.getName());
        fileContent = is;
    }
// ...
ds = new ByteArrayDataSource(fileContent, "image/jpeg"); 
attachment.setDataHandler(new DataHandler(ds));