Failed to convert value of type java.util.HashMap to String

Question

I have no idea how i can render this JSON on logcat :

The source code to get data from firebase realtime database :

FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myRef = database.getReference("hotel");

myRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        String value = dataSnapshot.getValue(String.class);
        Log.d(TAG, "Value is: " + value);
    }

    @Override
    public void onCancelled(DatabaseError error) {
        Log.w(TAG, "Failed to read value.", error.toException());
    }
});

It says error like this :

com.google.firebase.database.DatabaseException: Failed to convert value of type java.util.HashMap to String

I've tried some tutorial, but i can't find one. Also, i try this :

HashMap value = DataSnapshot.getValue(HashMap.class);

It ended up error as well. How should i render this HashMap data ?

it is database reference, you can see it on my question. i've just edited it. — Rido
– Rido, Commented Nov 29, 2017 at 2:28

Rohit Pal · Accepted Answer · 2019-07-12 12:10:51Z

21

You are getting HashMap of String as key and Object as Value so map it into something like below.

myRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
             Map<String, Object> map = (Map<String, Object>) dataSnapshot.getValue();
            Log.d(TAG, "Value is: " + map);
        }

        @Override
        public void onCancelled(DatabaseError error) {
            Log.w(TAG, "Failed to read value.", error.toException());
        }
    });

or we can get this parsed into some Model instead of an object.

update use this to parse

 Map<String, Object> map = (Map<String, Object>) dataSnapshot.getValue();

edited Jul 12, 2019 at 12:10

Rohit Pal

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answered Nov 28, 2017 at 15:44

vikas kumar

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4 Comments

Rido Over a year ago

I still got error :

com.google.firebase.database.DatabaseException: Class java.util.HashMap has generic type parameters, please use GenericTypeIndicator instead

vikas kumar Over a year ago

Then I need you Json what you have posted in the string

Rido Over a year ago

i just want to read data from database. I didn't include post yet.

vikas kumar Over a year ago

it's hard to tell what model you should follow without knowing which parent tag you are getting as database reference in code and full json

Alex Mamo · Accepted Answer · 2017-11-28 16:25:18Z

3

Assuming that the hotel node is a direct child of your Firebase root, to get those values, please use the following code

DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
DatabaseReference hotelRef = rootRef.child("hotel");
ValueEventListener eventListener = new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for(DataSnapshot ds : dataSnapshot.getChildren()) {
            String address = ds.child("address").getValue(String.class);
            String name = ds.child("name").getValue(String.class);
            Log.d("TAG", address + " / " + name);
        }
    }

    @Override
    public void onCancelled(DatabaseError databaseError) {}
};
hotelRef.addListenerForSingleValueEvent(eventListener);

The output will be:

Surubaya / Hotel Suridan
Bandung / Hotel Santika
//and so on

answered Nov 28, 2017 at 16:25

Alex Mamo

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2 Comments

Rido Over a year ago

Thank you, i will try it later

Alex Mamo Over a year ago

Ok and keep me posted.

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