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Quickstart: Azure Blob Storage client library for Java

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Note

The Build from scratch option walks you step by step through the process of creating a new project, installing packages, writing the code, and running a basic console app. This approach is recommended if you want to understand all the details involved in creating an app that connects to Azure Blob Storage. If you prefer to automate deployment tasks and start with a completed project, choose Start with a template.

Note

The Start with a template option uses the Azure Developer CLI to automate deployment tasks and starts you off with a completed project. This approach is recommended if you want to explore the code as quickly as possible without going through the setup tasks. If you prefer step by step instructions to build the app, choose Build from scratch.

Get started with the Azure Blob Storage client library for Java to manage blobs and containers.

In this article, you follow steps to install the package and try out example code for basic tasks.

In this article, you use the Azure Developer CLI to deploy Azure resources and run a completed console app with just a few commands.

Tip

If you're working with Azure Storage resources in a Spring application, we recommend that you consider Spring Cloud Azure as an alternative. Spring Cloud Azure is an open-source project that provides seamless Spring integration with Azure services. To learn more about Spring Cloud Azure, and to see an example using Blob Storage, see Upload a file to an Azure Storage Blob.

API reference documentation | Library source code | Package (Maven) | Samples

Prerequisites

Setting up

This section walks you through preparing a project to work with the Azure Blob Storage client library for Java.

Create the project

Create a Java application named blob-quickstart.

  1. In a console window (such as PowerShell or Bash), use Maven to create a new console app with the name blob-quickstart. Type the following mvn command to create a "Hello world!" Java project.

    mvn archetype:generate `
    --define interactiveMode=n `
    --define groupId=com.blobs.quickstart `
    --define artifactId=blob-quickstart `
    --define archetypeArtifactId=maven-archetype-quickstart `
    --define archetypeVersion=1.4

  2. The output from generating the project should look something like this:

    [INFO] Scanning for projects...
[INFO]
[INFO] ------------------< org.apache.maven:standalone-pom >-------------------
[INFO] Building Maven Stub Project (No POM) 1
[INFO] --------------------------------[ pom ]---------------------------------
[INFO]
[INFO] >>> maven-archetype-plugin:3.1.2:generate (default-cli) > generate-sources @ standalone-pom >>>
[INFO]
[INFO] <<< maven-archetype-plugin:3.1.2:generate (default-cli) < generate-sources @ standalone-pom <<<
[INFO]
[INFO]
[INFO] --- maven-archetype-plugin:3.1.2:generate (default-cli) @ standalone-pom ---
[INFO] Generating project in Batch mode
[INFO] ----------------------------------------------------------------------------
[INFO] Using following parameters for creating project from Archetype: maven-archetype-quickstart:1.4
[INFO] ----------------------------------------------------------------------------
[INFO] Parameter: groupId, Value: com.blobs.quickstart
[INFO] Parameter: artifactId, Value: blob-quickstart
[INFO] Parameter: version, Value: 1.0-SNAPSHOT
[INFO] Parameter: package, Value: com.blobs.quickstart
[INFO] Parameter: packageInPathFormat, Value: com/blobs/quickstart
[INFO] Parameter: version, Value: 1.0-SNAPSHOT
[INFO] Parameter: package, Value: com.blobs.quickstart
[INFO] Parameter: groupId, Value: com.blobs.quickstart
[INFO] Parameter: artifactId, Value: blob-quickstart
[INFO] Project created from Archetype in dir: C:\QuickStarts\blob-quickstart
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  7.056 s
[INFO] Finished at: 2019-10-23T11:09:21-07:00
[INFO] ------------------------------------------------------------------------
    ```

  3. Switch to the newly created blob-quickstart folder.

    cd blob-quickstart

  4. In side the blob-quickstart directory, create another directory called data. This folder is where the blob data files will be created and stored.

    mkdir data

Install the packages

Open the pom.xml file in your text editor.

Add azure-sdk-bom to take a dependency on the latest version of the library. In the following snippet, replace the {bom_version_to_target} placeholder with the version number. Using azure-sdk-bom keeps you from having to specify the version of each individual dependency. To learn more about the BOM, see the Azure SDK BOM README.

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>com.azure</groupId>
            <artifactId>azure-sdk-bom</artifactId>
            <version>{bom_version_to_target}</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

Then add the following dependency elements to the group of dependencies. The azure-identity dependency is needed for passwordless connections to Azure services.

<dependency>
    <groupId>com.azure</groupId>
    <artifactId>azure-storage-blob</artifactId>
</dependency>
<dependency>
    <groupId>com.azure</groupId>
    <artifactId>azure-identity</artifactId>
</dependency>

Set up the app framework

From the project directory, follow steps to create the basic structure of the app:

  1. Navigate to the /src/main/java/com/blobs/quickstart directory
  2. Open the App.java file in your editor
  3. Delete the line System.out.println("Hello world!");
  4. Add the necessary import directives

The code should resemble this framework:

package com.blobs.quickstart;

/**
 * Azure Blob Storage quickstart
 */
import com.azure.identity.*;
import com.azure.storage.blob.*;
import com.azure.storage.blob.models.*;
import java.io.*;

public class App
{
    public static void main(String[] args) throws IOException
    {
        // Quickstart code goes here
    }
}

With Azure Developer CLI installed, you can create a storage account and run the sample code with just a few commands. You can run the project in your local development environment, or in a DevContainer.

Initialize the Azure Developer CLI template and deploy resources

From an empty directory, follow these steps to initialize the azd template, provision Azure resources, and get started with the code:

  • Clone the quickstart repository assets from GitHub and initialize the template locally:

    azd init --template blob-storage-quickstart-java

    You'll be prompted for the following information:

    • Environment name: This value is used as a prefix for all Azure resources created by Azure Developer CLI. The name must be unique across all Azure subscriptions and must be between 3 and 24 characters long. The name can contain numbers and lowercase letters only.

  • Log in to Azure:

    azd auth login

  • Provision and deploy the resources to Azure:

    azd up

    You'll be prompted for the following information:

    • Subscription: The Azure subscription that your resources are deployed to.
    • Location: The Azure region where your resources are deployed.

    The deployment might take a few minutes to complete. The output from the azd up command includes the name of the newly created storage account, which you'll need later to run the code.

Run the sample code

At this point, the resources are deployed to Azure and the code is almost ready to run. Follow these steps to update the name of the storage account in the code, and run the sample console app:

  • Update the storage account name:
    1. In the local directory, navigate to the blob-quickstart/src/main/java/com/blobs/quickstart directory.
    2. Open the file named App.java in your editor. Find the <storage-account-name> placeholder and replace it with the actual name of the storage account created by the azd up command.
    3. Save the changes.
  • Run the project:
    1. Navigate to the blob-quickstart directory containing the pom.xml file. Compile the project by using the following mvn command: 
      mvn compile
    2. Package the compiled code in its distributable format: 
      mvn package
    3. Run the following mvn command to execute the app: 
      mvn exec:java
  • Observe the output: This app creates a test file in your local data folder and uploads it to a container in the storage account. The example then lists the blobs in the container and downloads the file with a new name so that you can compare the old and new files.

To learn more about how the sample code works, see Code examples.

When you're finished testing the code, see the Clean up resources section to delete the resources created by the azd up command.

Object model

Azure Blob Storage is optimized for storing massive amounts of unstructured data. Unstructured data doesn't adhere to a particular data model or definition, such as text or binary data. Blob storage offers three types of resources:

  • The storage account
  • A container in the storage account
  • A blob in the container

The following diagram shows the relationship between these resources.

Diagram of Blob storage architecture

Use the following Java classes to interact with these resources:

  • BlobServiceClient: The BlobServiceClient class allows you to manipulate Azure Storage resources and blob containers. The storage account provides the top-level namespace for the Blob service.
  • BlobServiceClientBuilder: The BlobServiceClientBuilder class provides a fluent builder API to help aid the configuration and instantiation of BlobServiceClient objects.
  • BlobContainerClient: The BlobContainerClient class allows you to manipulate Azure Storage containers and their blobs.
  • BlobClient: The BlobClient class allows you to manipulate Azure Storage blobs.
  • BlobItem: The BlobItem class represents individual blobs returned from a call to listBlobs.

Code examples

These example code snippets show you how to perform the following actions with the Azure Blob Storage client library for Java:

Important

Make sure you have the correct dependencies in pom.xml and the necessary directives for the code samples to work, as described in the setting up section.

Note

The Azure Developer CLI template includes a file with sample code already in place. The following examples provide detail for each part of the sample code. The template implements the recommended passwordless authentication method, as described in the Authenticate to Azure section. The connection string method is shown as an alternative, but isn't used in the template and isn't recommended for production code.

Authenticate to Azure and authorize access to blob data

Application requests to Azure Blob Storage must be authorized. Using the DefaultAzureCredential class provided by the Azure Identity client library is the recommended approach for implementing passwordless connections to Azure services in your code, including Blob Storage.

You can also authorize requests to Azure Blob Storage by using the account access key. However, this approach should be used with caution. Developers must be diligent to never expose the access key in an unsecure location. Anyone who has the access key is able to authorize requests against the storage account, and effectively has access to all the data. DefaultAzureCredential offers improved management and security benefits over the account key to allow passwordless authentication. Both options are demonstrated in the following example.

DefaultAzureCredential is a class provided by the Azure Identity client library for Java. DefaultAzureCredential supports multiple authentication methods and determines which method should be used at runtime. This approach enables your app to use different authentication methods in different environments (local vs. production) without implementing environment-specific code.

The order and locations in which DefaultAzureCredential looks for credentials can be found in the Azure Identity library overview.

For example, your app can authenticate using your Visual Studio Code sign-in credentials with when developing locally. Your app can then use a managed identity once it has been deployed to Azure. No code changes are required for this transition.

Assign roles to your Microsoft Entra user account

When developing locally, make sure that the user account that is accessing blob data has the correct permissions. You'll need Storage Blob Data Contributor to read and write blob data. To assign yourself this role, you'll need to be assigned the User Access Administrator role, or another role that includes the Microsoft.Authorization/roleAssignments/write action. You can assign Azure RBAC roles to a user using the Azure portal, Azure CLI, or Azure PowerShell. You can learn more about the available scopes for role assignments on the scope overview page.

In this scenario, you'll assign permissions to your user account, scoped to the storage account, to follow the Principle of Least Privilege. This practice gives users only the minimum permissions needed and creates more secure production environments.

The following example will assign the Storage Blob Data Contributor role to your user account, which provides both read and write access to blob data in your storage account.

Important

In most cases it will take a minute or two for the role assignment to propagate in Azure, but in rare cases it may take up to eight minutes. If you receive authentication errors when you first run your code, wait a few moments and try again.

  1. In the Azure portal, locate your storage account using the main search bar or left navigation.

  2. On the storage account overview page, select Access control (IAM) from the left-hand menu.

  3. On the Access control (IAM) page, select the Role assignments tab.

  4. Select + Add from the top menu and then Add role assignment from the resulting drop-down menu.

    A screenshot showing how to assign a role.

  5. Use the search box to filter the results to the desired role. For this example, search for Storage Blob Data Contributor and select the matching result and then choose Next.

  6. Under Assign access to, select User, group, or service principal, and then choose + Select members.

  7. In the dialog, search for your Microsoft Entra username (usually your user@domain email address) and then choose Select at the bottom of the dialog.

  8. Select Review + assign to go to the final page, and then Review + assign again to complete the process.

Sign-in and connect your app code to Azure using DefaultAzureCredential

You can authorize access to data in your storage account using the following steps:

  1. Make sure you're authenticated with the same Microsoft Entra account you assigned the role to on your storage account. You can authenticate via the Azure CLI, Visual Studio Code, or Azure PowerShell.

    Sign-in to Azure through the Azure CLI using the following command:

    az login

  2. To use DefaultAzureCredential, make sure that the azure-identity dependency is added in pom.xml:

    <dependency>
  <groupId>com.azure</groupId>
  <artifactId>azure-identity</artifactId>
</dependency>

  3. Add this code to the Main method. When the code runs on your local workstation, it will use the developer credentials of the prioritized tool you're logged into to authenticate to Azure, such as the Azure CLI or Visual Studio Code.

    /*
 * The default credential first checks environment variables for configuration
 * If environment configuration is incomplete, it will try managed identity
 */
DefaultAzureCredential defaultCredential = new DefaultAzureCredentialBuilder().build();

// Azure SDK client builders accept the credential as a parameter
// TODO: Replace <storage-account-name> with your actual storage account name
BlobServiceClient blobServiceClient = new BlobServiceClientBuilder()
        .endpoint("https://<storage-account-name>.blob.core.windows.net/")
        .credential(defaultCredential)
        .buildClient();

  4. Make sure to update the storage account name in the URI of your BlobServiceClient. The storage account name can be found on the overview page of the Azure portal.

    A screenshot showing how to find the storage account name.

    Note

    When deployed to Azure, this same code can be used to authorize requests to Azure Storage from an application running in Azure. However, you'll need to enable managed identity on your app in Azure. Then configure your storage account to allow that managed identity to connect. For detailed instructions on configuring this connection between Azure services, see the Auth from Azure-hosted apps tutorial.

Create a container

Create a new container in your storage account by calling the createBlobContainer method on the blobServiceClient object. In this example, the code appends a GUID value to the container name to ensure that it's unique.

Add this code to the end of the Main method:

// Create a unique name for the container
String containerName = "quickstartblobs" + java.util.UUID.randomUUID();

// Create the container and return a container client object
BlobContainerClient blobContainerClient = blobServiceClient.createBlobContainer(containerName);

To learn more about creating a container, and to explore more code samples, see Create a blob container with Java.

Important

Container names must be lowercase. For more information about naming containers and blobs, see Naming and Referencing Containers, Blobs, and Metadata.

Upload blobs to a container

Upload a blob to a container by calling the uploadFromFile method. The example code creates a text file in the local data directory to upload to the container.

Add this code to the end of the Main method:

// Create the ./data/ directory and a file for uploading and downloading
String localPath = "./data/";
new File(localPath).mkdirs();
String fileName = "quickstart" + java.util.UUID.randomUUID() + ".txt";

// Get a reference to a blob
BlobClient blobClient = blobContainerClient.getBlobClient(fileName);

// Write text to the file
FileWriter writer = null;
try
{
    writer = new FileWriter(localPath + fileName, true);
    writer.write("Hello, World!");
    writer.close();
}
catch (IOException ex)
{
    System.out.println(ex.getMessage());
}

System.out.println("\nUploading to Blob storage as blob:\n\t" + blobClient.getBlobUrl());

// Upload the blob
blobClient.uploadFromFile(localPath + fileName);

To learn more about uploading blobs, and to explore more code samples, see Upload a blob with Java.

List the blobs in a container

List the blobs in the container by calling the listBlobs method. In this case, only one blob has been added to the container, so the listing operation returns just that one blob.

Add this code to the end of the Main method:

System.out.println("\nListing blobs...");

// List the blob(s) in the container.
for (BlobItem blobItem : blobContainerClient.listBlobs()) {
    System.out.println("\t" + blobItem.getName());
}

To learn more about listing blobs, and to explore more code samples, see List blobs with Java.

Download blobs

Download the previously created blob by calling the downloadToFile method. The example code adds a suffix of "DOWNLOAD" to the file name so that you can see both files in local file system.

Add this code to the end of the Main method:

// Download the blob to a local file

// Append the string "DOWNLOAD" before the .txt extension for comparison purposes
String downloadFileName = fileName.replace(".txt", "DOWNLOAD.txt");

System.out.println("\nDownloading blob to\n\t " + localPath + downloadFileName);

blobClient.downloadToFile(localPath + downloadFileName);

To learn more about downloading blobs, and to explore more code samples, see Download a blob with Java.

Delete a container

The following code cleans up the resources the app created by removing the entire container using the delete method. It also deletes the local files created by the app.

The app pauses for user input by calling System.console().readLine() before it deletes the blob, container, and local files. This is a good chance to verify that the resources were created correctly, before they're deleted.

Add this code to the end of the Main method:

File downloadedFile = new File(localPath + downloadFileName);
File localFile = new File(localPath + fileName);

// Clean up resources
System.out.println("\nPress the Enter key to begin clean up");
System.console().readLine();

System.out.println("Deleting blob container...");
blobContainerClient.delete();

System.out.println("Deleting the local source and downloaded files...");
localFile.delete();
downloadedFile.delete();

System.out.println("Done");

To learn more about deleting a container, and to explore more code samples, see Delete and restore a blob container with Java.

Run the code

This app creates a test file in your local folder and uploads it to Blob storage. The example then lists the blobs in the container and downloads the file with a new name so that you can compare the old and new files.

Follow steps to compile, package, and run the code

  1. Navigate to the directory containing the pom.xml file and compile the project by using the following mvn command: 
    mvn compile
  2. Package the compiled code in its distributable format: 
    mvn package
  3. Run the following mvn command to execute the app: 
    mvn exec:java -D exec.mainClass=com.blobs.quickstart.App -D exec.cleanupDaemonThreads=false
    To simplify the run step, you can add exec-maven-plugin to pom.xml and configure as shown below: 
    <plugin>
  <groupId>org.codehaus.mojo</groupId>
  <artifactId>exec-maven-plugin</artifactId>
  <version>1.4.0</version>
  <configuration>
    <mainClass>com.blobs.quickstart.App</mainClass>
    <cleanupDaemonThreads>false</cleanupDaemonThreads>
  </configuration>
</plugin>
    With this configuration, you can execute the app with the following command: 
    mvn exec:java

The output of the app is similar to the following example (UUID values omitted for readability):

Azure Blob Storage - Java quickstart sample

Uploading to Blob storage as blob:
        https://mystorageacct.blob.core.windows.net/quickstartblobsUUID/quickstartUUID.txt

Listing blobs...
        quickstartUUID.txt

Downloading blob to
        ./data/quickstartUUIDDOWNLOAD.txt

Press the Enter key to begin clean up

Deleting blob container...
Deleting the local source and downloaded files...
Done

Before you begin the cleanup process, check your data folder for the two files. You can compare them and observe that they're identical.

Clean up resources

After you've verified the files and finished testing, press the Enter key to delete the test files along with the container you created in the storage account. You can also use Azure CLI to delete resources.

When you're done with the quickstart, you can clean up the resources you created by running the following command:

azd down

You'll be prompted to confirm the deletion of the resources. Enter y to confirm.

Next step

Azure Storage samples and developer guides for Java