Built a duplicate file finder in Java, here's how it works

Sheikh Muhammad Talha Bin Khalid — Sun, 01 Nov 2026 22:43:59 +0000

So I've been working on this little project called DupeLens. It's basically a Java CLI that finds duplicate files in your folders and generates an HTML report.

Nothing crazy, just something I thought would be useful.

Why I made it

I wanted a simple way to check which files were duplicated without worrying about accidentally deleting something important.

So I built one myself.

How it works

It's pretty straightforward.

First, it checks file sizes. If two files have different sizes, there's no reason to compare them further.

For files with matching sizes, it uses SHA-256 to check whether their contents are identical.

Once it's done, it shows the duplicates in the terminal. You can also generate an HTML report if you want something easier to look through.

And that's about it. It doesn't delete, move, or modify your files.

Wanna try it?

You'll need Java 17 or newer.

Download the JAR from GitHub and run:

java -jar dupelens.jar ./your-folder --html report.html

Then just open report.html in your browser.

What's next?

Just released v1.0.0, so it's still pretty early.

I'm thinking about adding exclusion patterns and JSON output, but I'm open to other ideas too.

If anyone wants to check out the code or suggest improvements, that'd be cool.

GitHub: https://github.com/illusionoftalha/dupelens

It's open-source and MIT-licensed.

DEV Community: Sheikh Muhammad Talha Bin Khalid

Built a duplicate file finder in Java, here's how it works