How to get response body using HttpURLConnection, when code other than 2xx is returned?

Question

I have problem with retrieving Json response in case when server returns error. See details below.

How I perform the request

I use java.net.HttpURLConnection. I setup request properties, then I do:

conn = (HttpURLConnection) url.openConnection();

After that, when request is successful, I get response Json:

br = new BufferedReader(new InputStreamReader((conn.getInputStream())));
sb = new StringBuilder();
String output;
while ((output = br.readLine()) != null) {
  sb.append(output);
}
return sb.toString();

... and the problem is:

I can't retrieve Json received when the server returns some error like 50x or 40x,. Following line throws IOException:

br = new BufferedReader(new InputStreamReader((conn.getInputStream())));
// throws java.io.IOException: Server returned HTTP response code: 401 for URL: www.example.com

The server sends body for sure, I see it in external tool Burp Suite:

HTTP/1.1 401 Unauthorized

{"type":"AuthApiException","message":"AuthApiException","errors":[{"field":"email","message":"Invalid username and/or password."}]}

I can get response message (i.e. "Internal Server Error") and code (i.e. "500") using following methods:

conn.getResponseMessage();
conn.getResponseCode();

But I can't retrieve request body... maybe there is some method I didn't notice in the library?

Answer 1

If the response code isn't 200 or 2xx, use getErrorStream() instead of getInputStream().