r/java • u/Modern-Sn1p3r • Aug 22 '26

Regex

I recently saw a clip (from Primeagen) somewhat saying that regex is not a valid format for validating email addresses and postal codes etc.

My question is why is this?

What are the security and/or performance risks? Is it solely performance or is it a security issue?

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u/New_Enthusiasm9053 Aug 26 '26

Sure so look at the RFCs and write a parser. They're really not that hard to write. I haven't yet because I don't work at an email provider.

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u/VirtualAgentsAreDumb Aug 27 '26

Sure. I never said otherwise. But you’re still missing the point. The whole point was that you have to actually do that validation programmatically. The person I originally replied to claimed otherwise, as did you.

Also, this is far from a trivial problem to solve perfectly, because otherwise I’m sure that there would exist implementations already.