J2EE design question: zipping files in memory vs hdd

It is commonly known to be a bad practice to use the java.io package in the J2EE world. I'm currently architecting an J2EE app that is supposed to fetch a couple of files from an external system (web service interface) and make a zip file including all the files for further processing. I'm debating whether or not I should store the files on the HDD (which I don't really like) or keep them in the memory. I did my math and I know the zipped "bundles" might be up to a couple MB large (with 20 concurrent users to start off with). I'd appreciate all your comments on how to implement this. Thanks!

[609 byte] By [fastolfa] at [2007-10-2 13:28:32]