Quickstart: Azure Blob storage client library v12 for Java

Get started with the Azure Blob storage client library v12 for Java. Azure Blob storage is Microsoft's object storage solution for the cloud. Follow steps to install the package and try out example code for basic tasks. Blob storage is optimized for storing massive amounts of unstructured data.

Note

To get started with the previous SDK version, see Quickstart: Azure Blob storage client library for Java.

Use the Azure Blob storage client library v12 for Java to:

  • Create a container
  • Upload a blob to Azure Storage
  • List all of the blobs in a container
  • Download a blob to your local computer
  • Delete a container

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

Note

The features described in this article are now available to accounts that have a hierarchical namespace. To review limitations, see the Known issues with Azure Data Lake Storage Gen2 article.

Prerequisites

Setting up

This section walks you through preparing a project to work with the Azure Blob storage client library v12 for Java.

Create the project

Create a Java Core application named blob-quickstart-v12.

  1. In a console window (such as cmd, PowerShell, or Bash), use Maven to create a new console app with the name blob-quickstart-v12. Type the following mvn command all on a single line to create a simple "Hello world!" Java project. The command is displayed here on multiple lines for readability.

    mvn archetype:generate -DgroupId=com.blobs.quickstart
                           -DartifactId=blob-quickstart-v12
                           -DarchetypeArtifactId=maven-archetype-quickstart
                           -DarchetypeVersion=1.4
                           -DinteractiveMode=false
    
  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-v12
    [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-v12
    [INFO] Project created from Archetype in dir: C:\QuickStarts\blob-quickstart-v12
    [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-v12 folder.

    cd blob-quickstart-v12
    
  4. In side the blob-quickstart-v12 directory, create another directory called data. This is where the blob data files will be created and stored.

    mkdir data
    

Install the package

Open the pom.xml file in your text editor. Add the following dependency element to the group of dependencies.

<dependency>
    <groupId>com.azure</groupId>
    <artifactId>azure-storage-blob</artifactId>
    <version>12.0.0</version>
</dependency>

Set up the app framework

From the project directory:

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

Here's the code:

package com.blobs.quickstart;

/**
 * Azure blob storage v12 SDK quickstart
 */
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
    {
    }
}

Copy your credentials from the Azure portal

When the sample application makes a request to Azure Storage, it must be authorized. To authorize a request, add your storage account credentials to the application as a connection string. View your storage account credentials by following these steps:

  1. Sign in to the Azure portal.

  2. Locate your storage account.

  3. In the Settings section of the storage account overview, select Access keys. Here, you can view your account access keys and the complete connection string for each key.

  4. Find the Connection string value under key1, and select the Copy button to copy the connection string. You will add the connection string value to an environment variable in the next step.

    Screenshot showing how to copy a connection string from the Azure portal

Configure your storage connection string

After you have copied your connection string, write it to a new environment variable on the local machine running the application. To set the environment variable, open a console window, and follow the instructions for your operating system. Replace <yourconnectionstring> with your actual connection string.

Windows

setx CONNECT_STR "<yourconnectionstring>"

After you add the environment variable in Windows, you must start a new instance of the command window.

Linux

export CONNECT_STR="<yourconnectionstring>"

macOS

export CONNECT_STR="<yourconnectionstring>"

Restart programs

After you add the environment variable, restart any running programs that will need to read the environment variable. For example, restart your development environment or editor before continuing.

Object model

Azure Blob storage is optimized for storing massive amounts of unstructured data. Unstructured data is data that does not 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 listBlobsFlat.

Code examples

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

Get the connection string

The code below retrieves the connection string for the storage account from the environment variable created in the Configure your storage connection string section.

Add this code inside the Main method:

System.out.println("Azure Blob storage v12 - Java quickstart sample\n");

// Retrieve the connection string for use with the application. The storage
// connection string is stored in an environment variable on the machine
// running the application called CONNECT_STR. If the environment variable
// is created after the application is launched in a console or with
// Visual Studio, the shell or application needs to be closed and reloaded
// to take the environment variable into account.
String connectStr = System.getenv("CONNECT_STR");

Create a container

Decide on a name for the new container. The code below appends a UUID value to the container name to ensure that it is unique.

Important

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

Next, create an instance of the BlobContainerClient class, then call the create method to actually create the container in your storage account.

Add this code to the end of the Main method:

// Create a BlobServiceClient object which will be used to create a container client
BlobServiceClient blobServiceClient = new BlobServiceClientBuilder().connectionString(connectStr).buildClient();

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

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

Upload blobs to a container

The following code snippet:

  1. Creates a text file in the local data directory.
  2. Gets a reference to a BlobClient object by calling the getBlobClient method on the container from the Create a container section.
  3. Uploads the local text file to the blob by calling the uploadFromFile method. This method creates the blob if it doesn't already exist, but will not overwrite it if it does.

Add this code to the end of the Main method:

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

// Write text to the file
FileWriter writer = new FileWriter(localPath + fileName, true);
writer.write("Hello, World!");
writer.close();

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

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

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

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 : containerClient.listBlobs()) {
    System.out.println("\t" + blobItem.getName());
}

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 so that you can see both files.
String downloadFileName = fileName.replace(".txt", "DOWNLOAD.txt");
File downloadedFile = new File(localPath + downloadFileName);

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

blobClient.downloadToFile(localPath + downloadFileName);

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 actually created correctly, before they are deleted.

Add this code to the end of the Main method:

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

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

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

System.out.println("Done");

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.

Navigate to the directory containing the pom.xml file and compile the project by using the following mvn command.

mvn compile

Then, build the package.

mvn package

Run the following mvn command to execute the app.

mvn exec:java -Dexec.mainClass="com.blobs.quickstart.App" -Dexec.cleanupDaemonThreads=false

The output of the app is similar to the following example:

Azure Blob storage v12 - Java quickstart sample

Uploading to Blob storage as blob:
        https://mystorageacct.blob.core.windows.net/quickstartblobsf9aa68a5-260e-47e6-bea2-2dcfcfa1fd9a/quickstarta9c3a53e-ae9d-4863-8b34-f3d807992d65.txt

Listing blobs...
        quickstarta9c3a53e-ae9d-4863-8b34-f3d807992d65.txt

Downloading blob to
        ./data/quickstarta9c3a53e-ae9d-4863-8b34-f3d807992d65DOWNLOAD.txt

Press the Enter key to begin clean up

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

Before you begin the clean up process, check your MyDocuments folder for the two files. You can open them and observe that they are identical.

After you've verified the files, press the Enter key to delete the test files and finish the demo.

Next steps

In this quickstart, you learned how to upload, download, and list blobs using Java.

To see Blob storage sample apps, continue to: