Adding new files to Zip archive

Re: Adding new files to Zip archive

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Aladdin wrote:
[color=blue]
> I am using the java.util.zip package to create zip files. I can
> create a new archive and add files to it without any trouble. But
> if I already have a zip file created, how do I add a new file to the
> archive without impacting the existing files? I looked through the
> APIs with no luck. I would rather avoid extracting all the files
> and rebuilding the archive from scratch if at all possible.
>
> Thanks
>
> -M[/color]

Hi,
I'm not familiar with the internal format of a ZIP file, but
rebuilding the file from scratch may be the only way any program can
do it. I'm not sure. I was interested, so I created a ZIP with two
files in it just now to look at. It seems that the files' data is
placed, along with the filenames, into the ZIP, and that immediately
following the last file is a table of contents with all the
filenames. This would imply that you cannot add data to a ZIP without
at least loading the table of contents, overwriting it, and rewriting
it at the new end of file. Anyway, if nobody comes up with a better
solution, remember that it's probably better to create a new,
temporary ZIP file, then transfer all the files via an in-memory
array from the old to the new, followed by finally placing your new
file in the new ZIP. This is probably faster than the other option,
which would be extracting all the contents of the old ZIP to actual
files, deleting it, then replacing it.

- --
Chris
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