Sample Fault Tolerant Java Utility Class to convert one or more Excel Files (XLS/XLSXs) to csv.
Seems like I go through this sort of exercise every few years - need to convert an excel spread sheet to comma separated format for subsequent processing. Two basic approaches - read the spreadsheet itself without using Excel (this approach) or rely upon an Excel installation and essentially write a small script that uses OLE automation and opens the xls/clsx, and does a "File-> Save As." This project is an example of the first approach.
This approach has the advantage of being cross platform and not relying on an Excel installation (and license). Also, there are sometimes problems with processes not terminating properly with OLE automation (maybe due to coding issues - but I recall relying upon a hack to find processes that were hanging around and just killing 'em -ugh).
The disadvantage to is approach is that it lags Excel versions a bit. There also can be a different result than what Excel File-->Save As functionality will do interactively (which can be difficult to explain to end users).
See also: