What is the Java equivalent to use https://fcm.googleapis.com/fcm/send REST Api

Question

I've already tried the following command in Curl to send a notification using the Firebase REST Api and it works:

curl -X POST --header "Authorization: key=AIza...iD9wk" --Header "Content-Type: application/json" https://fcm.googleapis.com/fcm/send -d "{\"notification\":{\"title\": \"My title\", \"text\": \"My text\", \"sound\": \"default\"}, \"to\": \"cAhmJfN...bNau9z\"}"

Now that I'm trying to do the same in Java, I couldn't find an easy way to do the same and nothing that I've tried triggers the notification in my mobile endpoint.

This is my closest approach:

    try {
        HttpURLConnection httpcon = (HttpURLConnection) ((new URL("https://fcm.googleapis.com/fcm/send").openConnection()));
        httpcon.setDoOutput(true);
        httpcon.setRequestProperty("Content-Type", "application/json");
        httpcon.setRequestProperty("Authorization: key", "AIza...iD9wk");
        httpcon.setRequestMethod("POST");
        httpcon.connect();
        System.out.println("Connected!");

        byte[] outputBytes = "{\"notification\":{\"title\": \"My title\", \"text\": \"My text\", \"sound\": \"default\"}, \"to\": \"cAhmJfN...bNau9z\"}".getBytes("UTF-8");
        OutputStream os = httpcon.getOutputStream();
        os.write(outputBytes);
        os.close();

        // Reading response
        InputStream input = httpcon.getInputStream();
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(input))) {
            for (String line; (line = reader.readLine()) != null;) {
                System.out.println(line);
            }
        }

        System.out.println("Http POST request sent!");
    } catch (IOException e) {
        e.printStackTrace();
    }

But then I get:

java.io.IOException: Server returned HTTP response code: 401 for URL: https://fcm.googleapis.com/fcm/send
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1625)
    at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:254)
    at httpclient.test.MyHttpClientPost.sendNotification(MyHttpClientPost.java:131)
    at httpclient.test.MyHttpClientPost.main(MyHttpClientPost.java:26)

Answer 1

401 means unauthorized, so no valid Authorization header was sent.

And this line:

httpcon.setRequestProperty("Authorization: key", "AIza...iD9wk");

Is not equivalent to -H "Authorization: key=AIza...iD9wk". The first argument should be the header name, which is Authorization:

httpcon.setRequestProperty("Authorization", "key=AIza...iD9wk");

In conclusion, you misunderstood how HTTP header is formatted. Basically the header name and value are separated by : not =.