How to get access token Using Service Account

I want to get access token using service account but the problem is where to put the json file ? How to link it . In doc section there is no proper guidelines . Do i need a asynctask ?

Here is the code :

    HttpTransport HTTP_TRANSPORT = new NetHttpTransport();
    JsonFactory JSON_FACTORY = new JacksonFactory();
    
    GoogleCredential credential = new GoogleCredential.Builder()
        .setTransport(HTTP_TRANSPORT)
        .setJsonFactory(JSON_FACTORY)
        .setServiceAccountId("")
        .setServiceAccountScopes("https://www.googleapis.com/auth/androidpublisher")
        .setServiceAccountPrivateKeyFromP12File(keyFile) // where to put the json file?
        .build();
      AccessToken accessToken = credentials.refreshAccessToken();

Steps for the getting access token from Service account.

  class MainActivity : AppCompatActivity() {
          override fun onCreate(savedInstanceState: Bundle?) {
                super.onCreate(savedInstanceState)
                setContentView(R.layout.activity_main)
                authExplicit()
            }
             fun authExplicit() {
                    CoroutineScope(Dispatchers.Default).launch {
                        try {
                            val credentials =
                                GoogleCredentials.fromStream(resources.assets.open("studentsamplechatbot-xvgloa.json"))
                                    .createScoped(Collections.singletonList("https://www.googleapis.com/auth/dialogflow"))
                            credentials.refreshIfExpired()
                            val accessToken = credentials.accessToken
                            Log.e("log_data", "Token :" + accessToken.tokenValue)
                            if (accessToken.tokenValue.isNotEmpty()) {
                                Log.e(
                                    "log_data",
                                    "Got it --> authenticationType :" + credentials.authenticationType
                                )
                                AuthToken = "Bearer " + accessToken.tokenValue
                            } else {
                                Log.e("log_data", "No token")
                                AuthToken = ""
                            }
                            CoroutineScope(Dispatchers.Main).launch {
                                initViews()
                            }
                        } catch (e: Exception) {
                            Log.e("log_data", e.toString())
                        }
                    }
                }
        }

You can download from Google Cloud Platform

1. Google Cloud Platform -> Select your Project -> IAM & Admin -> Service accounts -> Create Service Account

2. Create a Service Account will open one page there are several details that add details and create it.

3. After Creating a Service account, you can find a created service account on the list.

4. From the right side, there is actions column is there with three dots with each. from that, there is one option create key. When you click on that it will open one dialog with two options JSON and P12. When you select JSON and click on create, it will download the JSON file of your service account.

5. You can use this JSON file for your Android project and place it into an assets folder.
   Your Project -> app -> src -> main -> assets

6. You can use the above function for getting access token.