How to get access token from Spotify API? [java]

I am fairly new to programming with Java but am interested in creating a program that allows for connection to the Spotify API. I am using the Client Credential Flow authorization process but keep getting java.io.IOException: insufficient data written exception when trying to reach the access token. I cannot figure out what information I am missing to complete the request.

I found a YouTube video of the same process being completed in Python and they utilized the requests feature and .json() to receive the access token. Is there a similar way to complete this in Java?

        try {
    String str = "application/x-www-form-urlencoded";
    byte[]  hold = str.getBytes();
    
    //create url
    URL url = new URL(tokenURL);
    //open connection to url
    conn = (HttpURLConnection) url.openConnection();
    conn.setDoOutput(true); 
    conn.setDoInput(true);
    
    //setup post headers and body
    conn.setRequestMethod("POST");
    conn.setFixedLengthStreamingMode(32);
    conn.setRequestProperty("Authorization",String.format("Basic %s", clientCredEncode));
    conn.setRequestProperty("grant_type", "client_credentials");
    conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");
    conn.setRequestProperty("user-agent", "Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.85 Safari/537.36");
    
    //validate connection
    int val = conn.getResponseCode();
    String response = conn.getResponseMessage();
    System.out.println("response code: " + val);
    System.out.println("response: " + response);

    }catch(Exception e){
        System.out.println("error: " + e); 
        conn.disconnect();
    }

PYTHON CODE This code performs the action in python.

def spotifyAuth(clientID, clientSecret):
clientCred = f"{clientID}:{clientSecret}"
encodedClient = base64.b64encode(clientCred.encode())

tokenURL = "https://accounts.spotify.com/api/token"
method = "POST"

tokenData = {"grant_type" : "client_credentials"}

tokenHeader = {"Authorization" : f"Basic {encodedClient.decode()}"}

r = requests.post(tokenURL, data=tokenData, headers=tokenHeader)
tokenResponse = r.json()

accessToken = tokenResponse['access_token']
expires = tokenResponse['expires_in']

return accessToken, expires

Answer

Thanks to Rup I was able to identify the issue. I was not properly sending anything with the POST. I added .getOutputStream() so send the request and .getInputStream() to receive the response.

    //create url access point
    URL url = new URL(tokenURL);
    
    //open http connection to url
    conn = (HttpURLConnection) url.openConnection();
    conn.setDoOutput(true); 
    conn.setDoInput(true);
    
    //setup post function and request headers
    conn.setRequestMethod("POST");
    conn.setRequestProperty("Authorization",String.format("Basic %s", clientCredEncode));
    conn.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");

    //set body for posting
    String body = "grant_type=client_credentials";
    
    //calculate and set content length
    byte[] out = body.getBytes(StandardCharsets.UTF_8);
    int length = out.length; 
    conn.setFixedLengthStreamingMode(length);
    
    //connect to http
    conn.connect();
    //}
    
    //send bytes to spotify
    try(OutputStream os = conn.getOutputStream()) {
        os.write(out);
    }
    
    //receive access token
    InputStream result = conn.getInputStream();
    s = new String(result.readAllBytes());
    //System.out.println(s);