InputStream serviceAccount = new FileInputStream("json file path");
GoogleCredentials credentials = GoogleCredentials.fromStream(serviceAccount);
FirebaseOptions options = new FirebaseOptions.Builder()
    .setCredentials(credentials)
    .build();
FirebaseApp.initializeApp(options);
Firestore db = FirestoreClient.getFirestore();

<dependencies>
       <dependency>
           <groupId>com.google.firebase</groupId>
           <artifactId>firebase-admin</artifactId>
           <version>6.7.0</version>
       </dependency>
    </dependencies>