How To Figure Out The Required Headers For A Java REST Call?
When testing with the jsonplaceholder.typicode.com site java code does not need to set any headers. Reading the json from a URLConnection works fine. However other http endpoints will return a 403 Forbidden unless a HttpURLConnection is used and the User-Agent request property is set.
Is there a way other than trial and error to figure out the required headers for a given http endpoint?
Answer
There's nothing in the HTTP protocol that allows you to observe what headers a particular server is expecting. You send a request, and the server sends a response, that's all. (A nice server may, of course, choose to embed a helpful error message in its response.)
So the literal answer to your question is: no, there's no way to determine this beyond trial and error (unless you have access to documentation and/or source code).
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