HttpsURLConnection-发送POST请求

Question

I want to send a POST request to this particular API: https://developer.lufthansa.com/docs/read/api_basics/Getting_Started and I researched how to do that and tried everything but it simply doesn't work, I always get an HTTP 400 or an HTTP 401 error. Here's my code:

private void setAccessToken(String clientID, String clientSecret) {
    try {
        URL url = new URL(URL_BASE + "oauth/token");
        String params = "client_id=" + clientID + "&client_secret=" + clientSecret + "&grant_type=client_credentials";
        HttpsURLConnection connection = (HttpsURLConnection)url.openConnection();
        connection.setRequestMethod("POST");
        connection.setDoInput(true);
        connection.setDoOutput(true);
        connection.connect();
        OutputStreamWriter osw = new OutputStreamWriter(connection.getOutputStream());
        osw.write(params);
        BufferedReader br = new BufferedReader(new InputStreamReader(connection.getInputStream()));
        String line;
        while((line = br.readLine()) != null) {
            System.out.println(line);
        }
    } catch(IOException e) {
        e.printStackTrace();
    }
}

Kenta1561

Answer 1

Seems that your code is working well and it may be the case that you are providing invalid clientID or clientSecret so that your are getting wrong response in this case (as 401 indicates unauthorized). One thing you can do is you are only getting the response message if the http request status is ok (200). You may also get the invalid response message in case of 400 or 401 http response status. In order to print the invalid response messages you may follow the code below:

private void setAccessToken(String clientID, String clientSecret) throws Exception {

    String params = "client_id=" + clientID + "&client_secret=" + clientSecret + "&grant_type=client_credentials";
    URL obj = new URL(url);
    HttpsURLConnection con = (HttpsURLConnection) obj.openConnection();
    BufferedReader in;
    // add reuqest header
    con.setRequestMethod("POST");
    con.setRequestProperty("User-Agent", "Mozilla/5.0");
    con.setRequestProperty("Accept-Language", "en-US,en;q=0.5");

    // Send post request
    con.setDoOutput(true);
    DataOutputStream wr = new DataOutputStream(con.getOutputStream());
    wr.writeBytes(params);
    wr.flush();
    wr.close();

    int responseCode = con.getResponseCode();
    if (responseCode >= 400)
        in = new BufferedReader(new InputStreamReader(con.getErrorStream()));
    else 
        in = new BufferedReader(new InputStreamReader(con.getInputStream()));

    String inputLine;
    StringBuffer response = new StringBuffer();

    while ((inputLine = in.readLine()) != null) {
        response.append(inputLine);
    }
    in.close();

    System.out.println(response.toString());
}

In this way you can also get invalid response message. In your case when I tried to hit the provided api it is giving me the response below:

{"error": "invalid_client"}