KeyStore Explorer VS OpenSSL

Yes, that's clear but you need the private key to create a CSR. I'm guessing since you are using a Java app you should either have a JKS (old fashioned) or a P12 (pkcs12) keystore, one of those should contain the private key, you can use keystore explorer to extract the data. Https://keystore-explorer.org/. Source: about 1 year ago

Personally, I've also had decent experiences with Keystore Explorer: https://keystore-explorer.org/ I actually wrote about using it on my blog, which has plenty of screenshots: https://blog.kronis.dev/tutorials/lets-run-our-own-ca. - Source: Hacker News / over 1 year ago

Then let me tell you about keystore explorer https://keystore-explorer.org/ which will make your life a lot easier (and less chance that there are more then 1 keys inside your keystore. Source: over 1 year ago

I... Kind of like it? Not the fact that using such a GUI would be almost impossible, like the humorous example of an "engineer oriented UI" in the Silicon Valley series https://www.reddit.com/r/SiliconValleyHBO/comments/4nvvnl/pied_pipers_easytouse_tools/ which might be confusing for most people. But rather the fact that all of the complexity the software has is laid bare, so that nobody could mistakenly assume... - Source: Hacker News / almost 2 years ago

I suggest trying KeyStore Explorer. This tool supports most common certificate and wallet files. I have used in multiple occasions when standard tools couldn't do the task. Source: almost 2 years ago

Baserow uses open source like https://en.wikipedia.org/wiki/OpenSSL and can use it without handing over data to openssl.org. Source: over 1 year ago

Noob here; I'm looking at openssl.org Two commands are listed; "openssl-genrsa" and "openssl genrsa" (No hyphen). Source: about 2 years ago