I'm trying to retrieve all documents from my Firestore collection called "users', but I get an error message. I've tried to retrieve a single document too, but got the same error.

Error:

Database connection | Database.java

  public Firestore db;

public Database() throws IOException {
    // Use a service account
    try {

        InputStream serviceAccount = new FileInputStream("./serviceAccount.json");
        GoogleCredentials credentials = GoogleCredentials.fromStream(serviceAccount);
        FirebaseOptions options = FirebaseOptions.builder()
           .setCredentials(credentials)
           .setDatabaseUrl("https://riskgameverycool.firebaseio.com/")
           .build();

        FirebaseApp.initializeApp(options);
        System.out.println("Connection  GREAT Success!");
    } catch(Exception e) {
      //  Block of code to handle errors
      e.printStackTrace();
      System.out.println("Connection Failed.");
    }
}

Database.java:

public void getAllUsers() {
    try {
        // asynchronously retrieve all documents
        ApiFuture<QuerySnapshot> future = db.collection("users").get();
        // future.get() blocks on response
        List<QueryDocumentSnapshot> documents = future.get().getDocuments();
        for (QueryDocumentSnapshot document : documents) {
          System.out.println(document.getId()   " => "   document.toObject(User.class));
        }
    } catch(Exception e) {
        e.printStackTrace();
        System.out.println("Query messed up.");
    }
}

Firestore:

CodePudding user response：

As the error message says, your db field is never initialized. You probably want to do that in the Database() method:

db = FirestoreDatabase.getInstance();

Also see the Firebase documentation on initializing Firestore.