Creates a temporary file. Files are collected into one directory and by default are
deleted on exit from the VM. Files can be kept by defining the system property
poi.keep.tmp.files.
Dont forget to close all files or it might not be possible to delete them.
if (dir == null)
{
dir = new File(System.getProperty("java.io.tmpdir"), "poifiles");
dir.mkdir();
if (System.getProperty("poi.keep.tmp.files") == null)
dir.deleteOnExit();
}
File newFile = new File(dir, prefix + rnd.nextInt() + suffix);
if (System.getProperty("poi.keep.tmp.files") == null)
newFile.deleteOnExit();
return newFile;
