Download Files on Android

Cloud Storage allows developers to quickly and easily download files from a Google Cloud Storage bucket provided and managed by Firebase.

Create a Reference

To download a file, first create a Cloud Storage reference to the file you want to download.

You can create a reference by appending child paths to the storage root, or you can create a reference from an existing gs:// or https:// URL referencing an object in Cloud Storage.

// Create a storage reference from our app
StorageReference storageRef = storage.getReference();

// Create a reference with an initial file path and name
StorageReference pathReference = storageRef.child("images/stars.jpg");

// Create a reference to a file from a Google Cloud Storage URI
StorageReference gsReference = storage.getReferenceFromUrl("gs://bucket/images/stars.jpg");

// Create a reference from an HTTPS URL
// Note that in the URL, characters are URL escaped!
StorageReference httpsReference = storage.getReferenceFromUrl("https://firebasestorage.googleapis.com/b/bucket/o/images%20stars.jpg");

Download Files

Once you have a reference, you can download files from Cloud Storage by calling the getBytes() or getStream(). If you prefer to download the file with another library, you can get a download URL with getDownloadUrl().

Download in memory

Download the file to a byte[] with the getBytes() method. This is the easiest way to download a file, but it must load the entire contents of your file into memory. If you request a file larger than your app's available memory, your app will crash. To protect against memory issues, getBytes() takes a maximum amount of bytes to download. Set the maximum size to something you know your app can handle, or use another download method.

StorageReference islandRef = storageRef.child("images/island.jpg");

final long ONE_MEGABYTE = 1024 * 1024;
islandRef.getBytes(ONE_MEGABYTE).addOnSuccessListener(new OnSuccessListener<byte[]>() {
    @Override
    public void onSuccess(byte[] bytes) {
        // Data for "images/island.jpg" is returns, use this as needed
    }
}).addOnFailureListener(new OnFailureListener() {
    @Override
    public void onFailure(@NonNull Exception exception) {
        // Handle any errors
    }
});

Download to a local file

The getFile() method downloads a file directly to a local device. Use this if your users want to have access to the file while offline or to share the file in a different app. getFile() returns a DownloadTask which you can use to manage your download and monitor the status of the download.

islandRef = storageRef.child("images/island.jpg");

File localFile = File.createTempFile("images", "jpg");

islandRef.getFile(localFile).addOnSuccessListener(new OnSuccessListener<FileDownloadTask.TaskSnapshot>() {
    @Override
    public void onSuccess(FileDownloadTask.TaskSnapshot taskSnapshot) {
        // Local temp file has been created
    }
}).addOnFailureListener(new OnFailureListener() {
    @Override
    public void onFailure(@NonNull Exception exception) {
        // Handle any errors
    }
});

If you want to actively manage your download, see Manage Downloads for more information.

Download Data via URL

If you already have download infrastructure based around URLs, or just want a URL to share, you can get the download URL for a file by calling the getDownloadUrl() method on a storage reference.

storageRef.child("users/me/profile.png").getDownloadUrl().addOnSuccessListener(new OnSuccessListener<Uri>() {
    @Override
    public void onSuccess(Uri uri) {
        // Got the download URL for 'users/me/profile.png'
    }
}).addOnFailureListener(new OnFailureListener() {
    @Override
    public void onFailure(@NonNull Exception exception) {
        // Handle any errors
    }
});

Downloading Images with FirebaseUI

FirebaseUI provides simple, customizable, and production-ready native mobile bindings to eliminate boilerplate code and promote Google best practices. Using FirebaseUI you can quickly and easily download, cache, and display images from Cloud Storage using our integration with Glide.

First, add FirebaseUI to your app/build.gradle:

dependencies {
    // FirebaseUI Storage only
    compile 'com.firebaseui:firebase-ui-storage:0.6.0'
}

Then you can load images directly from Storage into an ImageView:

// Reference to an image file in Firebase Storage
StorageReference storageReference = ...;

// ImageView in your Activity
ImageView imageView = ...;

// Load the image using Glide
Glide.with(this /* context */)
        .using(new FirebaseImageLoader())
        .load(storageReference)
        .into(imageView);

Handle Activity Lifecycle Changes

Downloads continue in the background even after activity lifecycle changes (such as presenting a dialog or rotating the screen). Any listeners you had attached will also remain attached. This could cause unexpected results if they get called after the activity is stopped.

You can solve this problem by subscribing your listeners with an activity scope to automatically unregister them when the activity stops. Then, use the getActiveDownloadTasks method when the activity restarts to obtain download tasks that are still running or recently completed.

The example below demonstrates this and also shows how to persist the storage reference path used.

StorageReference mStorageRef;  //mStorageRef was previously used to transfer data.

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);

    // If there's a download in progress, save the reference so you can query it later
    if (mStorageRef != null) {
        outState.putString("reference", mStorageRef.toString());
    }
}

@Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
    super.onRestoreInstanceState(savedInstanceState);

    // If there was a download in progress, get its reference and create a new StorageReference
    final String stringRef = savedInstanceState.getString("reference");
    if (stringRef == null) {
        return;
    }
    mStorageRef = FirebaseStorage.getInstance().getReferenceFromUrl(stringRef);

    // Find all DownloadTasks under this StorageReference (in this example, there should be one)
    List<FileDownloadTask> tasks = mStorageRef.getActiveDownloadTasks();
    if (tasks.size() > 0) {
        // Get the task monitoring the download
        FileDownloadTask task = tasks.get(0);

        // Add new listeners to the task using an Activity scope
        task.addOnSuccessListener(this, new OnSuccessListener<FileDownloadTask.TaskSnapshot>() {
          @Override
          public void onSuccess(FileDownloadTask.TaskSnapshot state) {
             handleSuccess(state); //call a user defined function to handle the event.
          }
        });
    }
}

Handle Errors

There are a number of reasons why errors may occur on download, including the file not existing, or the user not having permission to access the desired file. More information on errors can be found in the Handle Errors section of the docs.

Full Example

A full example of a download with error handling is shown below:

storageRef.child("users/me/profile.png").getBytes(Long.MAX_VALUE).addOnSuccessListener(new OnSuccessListener<byte[]>() {
    @Override
    public void onSuccess(byte[] bytes) {
        // Use the bytes to display the image
    }
}).addOnFailureListener(new OnFailureListener() {
    @Override
    public void onFailure(@NonNull Exception exception) {
        // Handle any errors
    }
});

You can also get and update metadata for files that are stored in Cloud Storage.

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