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.
> > > > >
> > > > >
> > > > >
> > > > >
> > > >
> > >
> > >
> >
>
>
