[SOLVED] Server returned HTTP response code: 421 for URL:

Error added: 2022-04-12T08:14:17Z

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Answer 2714 (100.0% helpful)

This happened for me when Spring Boot was upgraded to 2.6.6.
The old code:

URL url = new URL(urlString);
HttpURLConnection urlc = (HttpURLConnection) url.openConnection();

worked before.
After the upgrade, it started failing.
I think it was due to the way it handled HTTP/2.0.

I changed to use HttpBuilder:

HttpClient.Builder builder = HttpClient.newBuilder()

This now works fine.

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