Check if URL exist on Firebase Database before add it

Question

I'm trying to upload images to Firebase Storage and add the download URL using getDownloadUrl() method to Firebase Database .

I want to check if the URL already exists in Firebase Database or not before adding it, I tried to split the URL using StringUtils.substringBetween(mUrl, "%2F", ".png") ; for example :

https://firebasestorage.googleapis.com/v0/b/app.appspot.com/o/Frames%2FAPP1565024974054.png

After Splitting I get this which is the name of the file :

APP1565024974054.png

So I can check if this string exists in Database or not before adding it.

Here's my code :

gettingURLs method: to get all URLs from Database and adding them to ArrayList.

private void gettingURLs(String mUrl) {
        ArrayList<String> arrayList = new ArrayList<>();
        mDatabase.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                for (DataSnapshot ds : dataSnapshot.getChildren()) {
                    String url = ds.child("url").getValue(String.class);
                    arrayList.add(url);
                }
                verification(arrayList, mUrl);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                Toast.makeText(createFrame.this, "Ops !,Something went wrong", Toast.LENGTH_SHORT).show();
            }
        });
    }

verification method : to check if URL exists or not

   private void verification(ArrayList<String> arrayList, String mUrl) {
        if (arrayList.size() > 0) {
            String PREFIX = StringUtils.substringBetween(mUrl, "%2F", ".png");
            for (String str : arrayList) {
                if (str.trim().contains(PREFIX)) {
                    Toast.makeText(createFrame.this, "Frame already uploaded, You don't need to upload it again", Toast.LENGTH_SHORT).show();
                    Helper.dismissProgressDialog();
                    break;
                } else {
                    addUrlToDataBase(mUrl, mDatabase);
                    break;
                }
            }
        } else
            addUrlToDataBase(mUrl, mDatabase);
    }

My issue :

code above adds all URLs although it already exists in the database, how I can check if URL exist before adding it

1 - If the URL exists, show Toast with

Toast.makeText(createFrame.this, "Frame already uploaded, You don't need to upload it again", Toast.LENGTH_SHORT).show();

2 - If the URL does not exist, Add it normally

Answer 1

Every time you upload an image to Firebase storage, you have the option of generating a downloadUrl. This download url is unique, this means that if you re-upload the same image again, you'll get a different url. Therefore, comparing downloadUrls is a bad idea as they will never match.

However, there is a way you can manipulate the file name to check whether the file already exists on Firebase storage. Simply create a reference with the file name in it and try to get a download url (before pushing). The response would be null if the file does not exist. Here's a little illustration:

void getReferenceAndLoadNewBackground(String photoName) {

    // edit this path to fit your own existing structure
    final StorageReference storageReference = FirebaseStorage.getInstance().getReference().child("photos").child(photoName + ".png");

    /* Now, here's where the big deal is.
     * If the image exists, onSuccess would be called.
     * If the image does not exist, onFailure would be called but you'll still need to get the particular error. */
    storageReference.getDownloadUrl()
        .addOnSuccessListener(new OnSuccessListener<Uri>() {
            @Override
            public void onSuccess(Uri uri) {
                // Yaay, the image exists, no need to re-upload.
            }
        })
        .addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception exception) {
                // this does not necessarily mean the image does not exist, we still need to check the error code
                int code = ((StorageException) exception).getErrorCode();
                if (code == StorageException.ERROR_OBJECT_NOT_FOUND) {

                    // haha, the image does not actually exist, upload it
                }
                else {
                    // handle all other problems here
                }

            }
        });
}

To learn more about the getDownloadUrl() function, you can check out this post or readthe documentation .

I hope this helps. Merry coding!

Answer 2

You should validate the file name before uploading it to FireStorage.

Your Realtime Database structure should be like this:

photos: {
   uid:{
          fileName:true
   }
}

So before sending the file to storage

private void shouldStore(String fileName) {
    rootRef.child("photos").child(uid).child(fileName).addValueEventListenerForSingleEvent(
         // ... if callback returns something dont upload
    )
}