Multipart/form-data and file attachment

Question

Hi ,
This question has probably been asked before, but if not then here it is. Any replies will be appreciated:
Q. When using "Enctype=Multipart/form-data", with file attachment alongwith other form fields, is it mandatory to attach a file ? What if user selects no file to attach?
Q. If no, then how can it be possible that a form can be submitted without attaching a file since when I try to submit a form with no file attached to it, it gives me error message saying :java.lang.NullPointerException
Q. Does it mean that I can't have a form with a blank "File" input field, if the form's Enctype is "multipart/form-data"? Since users may not select a file to attach to the form, in other words it is an optional.
I hope I was clear enough in explaining my questions.
Thanks in advance.

Answer 1

I am using Orielly's file attachement pacakge.
Here's what I am doing in my JSP page: It does the following:
int maxFileSize = 10 * 1024 * 1024; // 5MB max
String uploadDir = "/direct/files/upload/";
String FormResults = "";
String FileResults = "";
String fileName = "";
String fileName2 = "";
String paramName="";
String paramValue="";     
File f;
int filecounter=1;
first get the form fields using following code:
MultipartRequest multi = new MultipartRequest(request, uploadDir, maxFileSize);
Enumeration params = multi.getParameterNames();
//Get the form information
while (params.hasMoreElements())
     paramName = (String) params.nextElement();     
     paramValue = multi.getParameter(paramName);
     if (paramName.equals("emailconfirm"))
          emailconfirmation = paramValue;
     else if (paramName.equals("Requester"))
          Requester = paramValue;
     else if (paramName.equals("TodaysDate"))
          TodaysDate = paramValue;
     else if (paramName.equals("Extension"))
}//end while
Then it gets the file information using the following code: I have two file fields in my form so that's why I am using a filecounter to find out if user has attached two files or just one:
Enumeration files = multi.getFileNames();
while (files.hasMoreElements())
     String formName = (String) files.nextElement();
     if (filecounter == 2)
fileName2 = multi.getFilesystemName(formName);
     String fileType = multi.getContentType(formName);
          f = multi.getFile(formName);
     FileResults += "<BR>" + formName + "=" + fileName2 + ": Type= " + fileType + ":
Size= " + f.length();
     else
     {     fileName = multi.getFilesystemName(formName);
          String fileType = multi.getContentType(formName);
          f = multi.getFile(formName);
          FileResults += "<BR>" + formName + "=" + fileName + ": Type= " + fileType + ":
Size= " + f.length();
     filecounter=filecounter+1;
Then after composing the mail message I send email with the form fields and file attachments using following code:
Properties props = new Properties();
MimeBodyPart mbp1 = new MimeBodyPart();
MimeBodyPart mbp2 = new MimeBodyPart();
MimeBodyPart mbp3 = new MimeBodyPart();
URLDecoder urlDecoder = new URLDecoder();
String to1 = urlDecoder.decode(toemail);
String from1 = urlDecoder.decode(fromemail);
String cc1 = urlDecoder.decode(ccemail);
props.put( "mail.host", host );
Session session1 = Session.getDefaultInstance(props, null);
// Construct the message
Message msg = new MimeMessage( session1 );
msg.setFrom( new InternetAddress( from1 ) );
msg.setRecipients( Message.RecipientType.TO, InternetAddress.parse( to1, false ) );
msg.setRecipients( Message.RecipientType.CC, InternetAddress.parse( cc1, false ) );
msg.setSubject( subject );
msg.setHeader( "X-Mailer", "ExceptionErrorMail" );
msg.setSentDate( new Date() );
mbp1.setText(mail_message);
mbp1.setContent(mail_message, "text/html");
// Send the email message
FileDataSource fds = new FileDataSource(uploadDir + fileName);
FileDataSource fds2 = new FileDataSource(uploadDir + fileName2);
mbp2.setDataHandler(new DataHandler(fds));
mbp3.setDataHandler(new DataHandler(fds2));
mbp2.setFileName(fileName);
mbp3.setFileName(fileName2);
Multipart mp = new MimeMultipart();
mp.addBodyPart(mbp1);
mp.addBodyPart(mbp2);
mp.addBodyPart(mbp3);
msg.setContent(mp);
Transport.send( msg );
//email sent...
//delete the two files from the server..
File f2 =new File(uploadDir + fileName);
f2.delete();
File f3 =new File(uploadDir + fileName2);
f3.delete();     
//End of code
So when I don't attach a file and submit my form , I get the error message that I mentioned in my previous post.
Any more ideas?