Exercise - Get blob references

  • 10 minutes

To interact with a container in Blob Storage, use a BlobContainerClient object. In addition to creating containers as you saw in the last unit, a BlobContainerClient object can also be used to list the blobs in a container.

Listing blobs in a container

Get a list of the blobs in a container using BlobContainerClient's GetBlobsAsync method. Behind the scenes, the client makes one or more HTTP calls to Azure to list all of the blobs in the container. Since this method is asynchronous, you need to await the results as you read them. They might not all be returned in a single HTTP call. The following code shows the standard pattern for reading the results with a foreach loop.

AsyncPageable<BlobItem> blobs = containerClient.GetBlobsAsync();

await foreach (var blob in blobs)
{
    // Read the BlobItem and work with it here
}

You can get a list of the blobs in a container using the listBlobs method in BlobContainerClient. Behind the scenes, the client makes one or more HTTP calls to Azure to list all of the blobs in the container. This method returns PagedIterable<BlobItem> that implements Iterable<BlobItem>. You can then read it one item at a time or by page of items. The following code shows the standard pattern for reading the results with a for loop.

for (BlobItem blob : blobContainerClient.listBlobs()) {
    // Read the BlobItem and work with it here
}

blobContainerClient.listBlobs()
    .stream()
    .map(blobItem -> /* Read the BlobItem and work with it here */)
    .collect(Collectors.toList());

Exercise

One of the features in your app requires getting a list of blobs from the API. Use the pattern previously shown to list all the blobs in our container. As you process the list, you get the name of each blob.

Using the editor, replace GetNames in BlobStorage.cs with the following code, and save your changes.

public async Task<IEnumerable<string>> GetNames()
{
    List<string> names = new List<string>();

    BlobServiceClient blobServiceClient = new BlobServiceClient(storageConfig.ConnectionString);

    // Get the container the blobs are saved in
    BlobContainerClient containerClient = blobServiceClient.GetBlobContainerClient(storageConfig.FileContainerName);

    // This gets the info about the blobs in the container
    AsyncPageable<BlobItem> blobs = containerClient.GetBlobsAsync();

    await foreach (var blob in blobs)
    {
        names.Add(blob.Name);
    }
    return names;
}

The FilesController processes the names that this method returns to turn the names into URLs. When returned to the client, the names are rendered as hyperlinks on the page.

Using the editor, replace listNames in BlobStorage.java with the following code, and save your changes.

public List<String> listNames() {
    return blobContainerClient.listBlobs()
      .stream()
      .map(BlobItem::getName)
      .collect(Collectors.toList());
}

IndexBean and index.xhmtl process the names returned by this method to be rendered as hyperlinks on the page.