当 Java 出现 401 Unauthorized 错误时，如何捕获 POST 请求的 json 响应？

Question

I have the following API:

https://mrcheff.herokuapp.com/v1/api/usuarios/login

It is used to perform authentication passing username and password as parameters in the request body and I need to get the json that returns when the informed user is incorrect or the informed password is incorrect!

In this case, by typing the incorrect user, I return the json:

"errors": "Usuario não registrado"

And by typing the wrong password I get the json return:

"errors": "Senha inválida"

My request looks like this:

try {
   String linkApi = getLinkApi().getProperty("linkApi");
   URL url = new URL(linkApi.concat("/api/usuarios/login"));
   con = (HttpURLConnection) url.openConnection();
   con.setRequestProperty("Content-Type", "application/json");
   con.setRequestMethod("POST");
   con.setDoOutput(true);
   login = new Login();
   gson = new Gson();
   login.setEmail("email@email.com");
   login.setPassword("senha123");
   String input = gson.toJson(login);
   System.out.println(input);
   System.out.println("");
   OutputStream os = con.getOutputStream();
   os.write(input.getBytes());
   os.flush();
   int responseCode = con.getResponseCode();
   System.out.println("Código: " + responseCode);
   System.out.println("");
   BufferedReader br = new BufferedReader(new InputStreamReader((con.getInputStream())));
   String output;
   StringBuffer response = new StringBuffer();
   while ((output = br.readLine()) != null) {
       response.append(output);
   }
   br.close();
   System.out.println(response.toString());
   System.out.println("");
} catch(MalformedURLException e) {
   System.out.println("Houve um erro. Exception: " + e.getMessage());
   return false;
} catch (IOException e) {
   System.out.println("Houve um erro. Exception: " + e.getMessage());
   return false;
} finally {
   con.disconnect();
}

Everything flows well until you get to that part of the code:

BufferedReader br = new BufferedReader(new InputStreamReader((con.getInputStream())));

Because arriving at this line, if the error is 401, it falls in the catch and returns me only that it gave the error 401.. how do I get the json's?

Answer 1

If the response code is less than 400 you can use getInputStream() otherwise you can use getErrorStream() instead of getInputStream().

BufferedReader br = null;
if (100 <= con.getResponseCode() && con.getResponseCode() < 400) {
    br = new BufferedReader(new InputStreamReader(con.getInputStream()));
} else {
    br = new BufferedReader(new InputStreamReader(con.getErrorStream()));
}

If the connection was not connected, or if the server did not have an error while connecting or if the server had an error but no error data was sent, getErrorStream method will return null.