https://curl.se/ has been account free since 1998.
Never understood why people keep trying to use proprietary tools for this, especially when curl is so good.
I have a directory of shell scripts I use to test out endpoints. I persist request/response data either with environment variables or regular files. Oh and since these are just shell scripts, it’s pretty trivial to do stuff like iterate over a CSV (or JSON array) and make a request for each row, conditionally make requests, or whatever else you want.
Oh and honorable mention goes to jo and jq for making it super easy to make/process JSON data.
Never do certifications for software engineering. The only certifications worth a damn are security certs and networking certs. If I saw a programming-related certification on a resume, I would completely ignore it since the only thing it tells me is that you paid some money to get a cert.
While I’m not a fan of Java, it’s most certainly not a dying language and you will be able to easily find employment into perpetuity. If I had to pick, I’d personally choose Java over .NET purely to avoid being trapped in Microsoft-land, especially with all of the bullshit they’ve been up to lately.