How to know the file size when uploading via multipart form-data?

问题

I am exercising a simple application with HTML client that uploads a file to the server and must display a progress bar :)

The server is servlet-based, some servlet receives the multipart content, parses it etc. Obviously, at every moment I know the number of bytes received so far. However in order to supply an info for the progress bar on the client side a servlet also needs the total number of bytes for the file, which is being uploaded. Any idea where to get the total number of bytes from please?

Thanks!

回答1:

Size of content are placed in Content-Length header (see rfc2616). In Servlet you can get this header's value by request.getContentLength() or reqest.getHeaders("Content-Length")

回答2:

I think you have to implement the progress bar in javascript on the client side.

Anyway, this link gives an explanation of how to do it using JQuery.

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The server can obtain the size of the multipart being uploaded from the HTTP request header; see @ilya's answer. However, getting that information and the count(s) of bytes read so far into a stream of HTTP responses that display or update a progress bar would be rather complicated ...

来源：https://stackoverflow.com/questions/5920689/how-to-know-the-file-size-when-uploading-via-multipart-form-data