When building a war file with ant, I found it convenient to include multiple <webinf/> elements in the war task when some of the WEB-INF files were generated, so that the source files and the generated files could be in separate directory trees. However, if there were entries under WEB-INF that were duplicated between the directory trees, one of them would always cause ant to find the war file out of date and rebuild it. It's not that I had any duplicated regular files, but I did have duplicated subdirectories, which had different timestamps. I had been puzzled by why ant was always rebuilding the war file, even if nothing had changed, before looking into it. I finally changed the war task to have a single <webinf/> element pointing at the generated files, and added a task that copies the source files into the directory tree of the generated files.