Java.util.zip: how to save file type

Question

HI,
I have a written a program that zips PDF files and sends them as an attachment via email. This have been running daily for the last 1.5 years with no problems. Recently, some email providers have been striping the attachments or refusing the email, because I have used two file suffix on the attachment, e.g report.pdf.zip. I did this so that when the file is unzipped the .pdf extension remains and file is recognised, otherwise the document is treated as plain text or unknown format. How can I include the filetype in the zipped file, so that I can have report.pdf become report.zip, then when the user unzips the file has report.zip become report.pdf. I know the filetype is stored in the zip header, but I don't know how to do this using java.util.zip. Any help would be appreciated.
Mike

Answer 1

You see, zip files are inherently dumb. They don't "actually" have a file system in the strictest sense. The zip file format merely associates a String ID with some bytes. It's all on the client side where the magic happens. if I have three zip entries in a file, these are the entry names.
1.) somedir/myfile.txt
2.) someotherdir/myfile.txt
3.) README
when a client "unzipper" see these names, it realizes that "/" is a directory separator, so it makes the appropriate directories and places the bytes into files of that given name.
So all you should have to do is make the zip entry with a name that ends in .pdf The client should do the rest.