How to Convert XLS to XLSX in Java

Why Upgrading XLS to XLSX Is Worth Your Time Ask any seasoned Java developer who's worked with Excel files long enough, and you’ll probably hear a similar refrain: the old XLS Excel format is clunky and annoying. It’s been around since the late ’80s, and while it’s still supported in a lot of systems, it's not doing us many favors today.  It was, after all, replaced with XLSX for a reason. Unfortunately, there’s still a lot of important data packed in those old binary XLS containers, and some developers are tasked with making clean conversions to XLSX to improve the usability (and security) of that data for the long run.