So do you simultaneously write to a file while reading a String parameter
when you process a form? What parts of the multipart request do we save in
the bean, and in what scope?
----- Original Message -----
From: "Martin Cooper" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>; "Jonathan Asbell" <[EMAIL PROTECTED]>
Sent: Monday, June 11, 2001 1:23 AM
Subject: Re: uploading file requires immediate serialization location?
> Yes, I think you've got it. Just to be clear, though, when you say "we
need
> to examine the sections in the header ...", the "we" here is Struts - you
> don't need to do anything in your application. Struts makes getParameter()
> et all work for multipart requests as well as regular requests.
>
> What you are seeing in the packages you've looked at is the parsing of a
> MIME part. The fields in a multipart/form-data request each conform to the
> specification for a MIME part, and they are separated by a boundary, which
> is a line containing a pattern defined in a header at the top of the
> request.
>
> Each MIME part consists of a sequence of MIME headers, followed by a blank
> line, followed by the data for that MIME part, known as the body. A MIME
> header takes the form "header-name: value" - for example, "Content-type:
> text/plain". The body is just a bunch of data that conforms to the
> statements made about it in the headers.
>
> Every field in a multipart request is encoded this way. So where a regular
> query using GET might contain a query string like this:
>
> ...&author=Martin&...
>
> a multipart request would represent the same query parameter like this:
>
> -----------------------------0123456789--
> Content-disposition: form-data; name="author"
>
> Martin
> -----------------------------0123456789--
>
> For a file upload, the difference is only that the Content-disposition
> header will include a file name, and the data can be binary if necessary.
>
> When a multipart handler processes a request, it is reading the data from
an
> input stream provided by the container. Typically, for regular query
> parameters, it will store the value in a hash table. For file parameters,
it
> will store the data in a file and retain information about that file. The
> Struts implementation uses the FormFile interface to provide access to
that
> information.
>
> A multipart implementation could do whatever it wanted to with the data
> provided from a file upload. Although the Content-disposition header may
> specify a file name, there is no requirement to store that data as a file.
> One implementation that would make sense would be to define a size
> threshold, and store uploaded objects below that size in memory, while
> writing larger ones to disk.
>
> Regarding form beans and binary data, there is no reason why a field in a
> form bean cannot be a byte array. However, by itself that is not very
> useful, hence the FormFile interface. If you'll notice, that interface
does
> in fact have a getFileData() method, which will give you the uploaded data
> as a byte array. In the current implementation, what that actually does is
> load the contents of the file into memory and hand you back that memory.
And
> there you have binary data in a form field.
>
> Hope this helps.
>
> --
> Martin Cooper
>
>
> ----- Original Message -----
> From: "Jonathan Asbell" <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>
> Sent: Sunday, June 10, 2001 1:19 PM
> Subject: Re: uploading file requires immediate serialization location?
>
>
> > Martin, you seem to understand this subject well, so let me take a shot
> and
> > tell me if I am correct:
> >
> > A multi-part request is a request, but a different one. That is, with a
> > regular request things have been abstracted for us nicely with
> > "getParameter" etc., but a request submitted as multipart is not handled
> > nicely for us by the servlet spec and is a whole different animal. This
> > type of request needs to be handled uniquely (though I dont understand
why
> > the servlet spec does not have standard abstractions for it), because it
> may
> > contain binary non-text content accompanied by regular content. In such
a
> > request we need to examine the sections in the header and parse for
> certain
> > values we are expecting to separate out the regular text values
submitted
> > from the binary parts, and then handle the binary parts.
> >
> > Things I still dont get:
> > In all packages I have examined that handle multipart requests, there is
> > always a notion of looking for the line ": ", then looking for the blank
> > line after that, and then reading in binary values that follow the blank
> > line up until the "boundry" which is a String in a known format (see
link
> > below). What I dont understand is what are our options in handling this
> > binary stuff which is not text. Most packages I have seen write it to a
> > file. I'm not sure if there is a way to save a binary object at all,
let
> > alone save it in a filed value in a bean. How do you store a binary
> object
> > in a field?
> >
> > ==============
> > REFERENCE
> > ==============
> > For those interested see this article:
> > www.onjava.com/lpt/a//onjava/2001/04/05/upload.html
> > Available servlet packages http://www.servlets.com/cos/index.html
> >
> >
> >
> > ----- Original Message -----
> > From: "Martin Cooper" <[EMAIL PROTECTED]>
> > To: "Jonathan Asbell" <[EMAIL PROTECTED]>
> > Cc: <[EMAIL PROTECTED]>
> > Sent: Sunday, June 10, 2001 3:01 PM
> > Subject: Re: uploading file requires immediate serialization location?
> >
> >
> > > Good question. What you are really asking is "what does the
<html:file>
> > tag
> > > do?".
> > >
> > > Struts will generate an <input type="file" ... > tag, where the value
of
> > the
> > > 'name' attribute is taken from the 'property' attribute of your
> > <html:file>
> > > tag. It will also generate a 'value' attribute. Looking at the source
> > code,
> > > it seems that the valueof the 'value' attribute will be the result of
> > > calling toString() on the FormFile object. Since that object doesn't
> > > override toString(), the result will be nothing useful. On the other
> hand,
> > > browsers usually ignore the 'value' attribute anyway.
> > >
> > > At this point, the original uploaded file is still on the disk, and
will
> > > remain there until the form is resubmitted. Then it will be deleted as
a
> > > part of setting up for parsing the new multipart data.
> > >
> > > Hope this helps.
> > >
> > > --
> > > Martin Cooper
> > >
> > >
> > > ----- Original Message -----
> > > From: "Jonathan Asbell" <[EMAIL PROTECTED]>
> > > To: "Martin Cooper" <[EMAIL PROTECTED]>
> > > Sent: Sunday, June 10, 2001 5:47 AM
> > > Subject: Re: uploading file requires immediate serialization location?
> > >
> > >
> > > > Great explanation Martin. Thank you. So what you really have said
is
> > that
> > > > the stream contents gets turned into a FormFile object. Ok. Now
the
> > big
> > > > question. You know when a form is not valid it gets sent beack to
the
> > > > client as strings which pre-populate the form fields. How will this
> > occur
> > > > in the case of a file input?
> > > >
> > > >
> > > > ----- Original Message -----
> > > > From: "Martin Cooper" <[EMAIL PROTECTED]>
> > > > To: <[EMAIL PROTECTED]>; "Jonathan Asbell"
> > > <[EMAIL PROTECTED]>
> > > > Sent: Sunday, June 10, 2001 12:20 AM
> > > > Subject: Re: uploading file requires immediate serialization
location?
> > > >
> > > >
> > > > > Let me see if I can describe the process.
> > > > >
> > > > > 1. Check to see if the request should be treated as multipart
(i.e.
> > > > content
> > > > > type is multipart/form-data and method is POST). If not, carry on
as
> > > > normal.
> > > > > 2. Find the multipart handler or instantiate one, set it on the
form
> > > bean,
> > > > > and call it to handle the request.
> > > > > 2a. Iterate over the fields (parts) in the request.
> > > > > 2a1. If the current part is not a file, store it as a String.
> > > > > 2a2. If the current part is a file (according to the
> > Content-Disposition
> > > > > header), create a new file in the temp directory, stream the
content
> > of
> > > > the
> > > > > part to that file, create a new object which implements FormFile,
> and
> > > > store
> > > > > the file data in it.
> > > > > 2b. Turn the set of fields into something that looks like regular
> > > request
> > > > > parameters.
> > > > > 3. Populate the ActionForm instance from the set of request
> > parameters.
> > > > > Here, the value of a file parameter has type FormFile, so it
matches
> a
> > > > > setter on the form bean that takes a FormFile as a parameter.
> > > > >
> > > > > That's the gist of it, although there are some other nitty gritty
> > > details.
> > > > > Almost all of this happens inside the code that populates the form
> > bean
> > > > from
> > > > > request parameters.
> > > > >
> > > > > It appears (from my reading of the source, anyway) that the
> temporary
> > > > files
> > > > > will not be automatically deleted until another request comes in
> that
> > > uses
> > > > > the same form bean instance, or until the form bean instance goes
> > away.
> > > > > Given that, I would recommend calling
> setMultipartRequestHandler(null)
> > > > from
> > > > > your form bean's reset() method if you keep your beans in session
> > scope.
> > > > >
> > > > > The part you are interested in, I believe, is 2a2 above.
> > Unfortunately,
> > > > that
> > > > > code is buried inside an iterator class, so you can't override
just
> > that
> > > > > piece. I assume what you would want is that the data is kept in
> memory
> > > > > instead of to a file. Interestingly, I believe the original
> > > implementation
> > > > > did this, but it was changed to use files because of potential
> memory
> > > > > problems with large uploads.
> > > > >
> > > > > Hope this helps.
> > > > >
> > > > > --
> > > > > Martin Cooper
> > > > >
> > > > >
> > > > > ----- Original Message -----
> > > > > From: "Jonathan Asbell" <[EMAIL PROTECTED]>
> > > > > To: <[EMAIL PROTECTED]>
> > > > > Sent: Saturday, June 09, 2001 8:11 PM
> > > > > Subject: Re: uploading file requires immediate serialization
> location?
> > > > >
> > > > >
> > > > > > Hello Martin. So is it POSSIBLE to save binary data in a bean?
> > What
> > > > does
> > > > > > struts do? These are my real questions. If I have a form which
> > > besides
> > > > > > fields, has an uploaded file, how does the bean actually handle
> the
> > > > file?
> > > > > > Is there a conceptual step by step you can give me. How does
the
> > > > > ActionForm
> > > > > > save (and validate) the binary data sent via input type "file".
> > > > > >
> > > > > >
> > > > > > ----- Original Message -----
> > > > > > From: "Martin Cooper" <[EMAIL PROTECTED]>
> > > > > > To: <[EMAIL PROTECTED]>; "Jonathan Asbell"
> > > > > <[EMAIL PROTECTED]>
> > > > > > Sent: Saturday, June 09, 2001 10:55 PM
> > > > > > Subject: Re: uploading file requires immediate serialization
> > location?
> > > > > >
> > > > > >
> > > > > > > Internally to Struts, multipart handling is provided through
an
> > > > > interface,
> > > > > > > MultipartRequestHandler. In Struts 1.0, the only supplied
> > > > implementation
> > > > > > of
> > > > > > > this interface is DiskMultipartRequestHandler, which, as you
> might
> > > > > expect,
> > > > > > > writes "file" parts to disk as it encounters them.
> > > > > > >
> > > > > > > Struts does allow you to configure the multipart handler to
use,
> > by
> > > > > > > specifying the class name in the multipartClass init-param for
> > your
> > > > web
> > > > > > app.
> > > > > > > This allows you to provide your own implementation if you want
> to
> > > > > > (although
> > > > > > > this is no small task).
> > > > > > >
> > > > > > > --
> > > > > > > Martin Cooper
> > > > > > >
> > > > > > >
> > > > > > > ----- Original Message -----
> > > > > > > From: "Jonathan Asbell" <[EMAIL PROTECTED]>
> > > > > > > To: <[EMAIL PROTECTED]>
> > > > > > > Sent: Saturday, June 09, 2001 6:39 AM
> > > > > > > Subject: uploading file requires immediate serialization
> location?
> > > > > > >
> > > > > > >
> > > > > > > Hello all.
> > > > > > > I am just trying to understand an aspect of a multipart
request.
> > > When
> > > > > > > you submit after using an input of type "file", do you have to
> > > provide
> > > > > > > an immediate location for the file to be serialized to, or can
> you
> > > > store
> > > > > > > it in a java object (in a bean's field) as a binary object
until
> > you
> > > > are
> > > > > > > ready to serialize it. The reason is that I want to hold a
jpeg
> > in
> > > a
> > > > > > > bean until the person completes the last page of the form, and
> > THEN
> > > > > > > serialize it.
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > > >
> > > >
> > >
> > >
> >
>
>
