In addition to the data they contain, blobs support system properties and user-defined metadata. This article shows how to manage system properties and user-defined metadata with theAzure Storage client library for Java.

Prerequisites

• Azure subscription -create one for free
• Azure storage account -create a storage account
• Java Development Kit (JDK) version 8 or later (we recommend version 17 for the best experience)
• Apache Maven is used for project management in this example

Set up your environment

If you don't have an existing project, this section shows you how to set up a project to work with the Azure Blob Storage client library for Java. For more information, seeGet started with Azure Blob Storage and Java.

To work with the code examples in this article, follow these steps to set up your project.

Install packages

Open thepom.xml file in your text editor. Install the packages byincluding the BOM file, orincluding a direct dependency.

Add import statements

Add the followingimport statements:

import com.azure.storage.blob.*;import com.azure.storage.blob.models.*;import java.util.*;

Authorization

The authorization mechanism must have the necessary permissions to work with container properties or metadata. For authorization with Microsoft Entra ID (recommended), you need Azure RBAC built-in roleStorage Blob Data Reader or higher for theget operations, andStorage Blob Data Contributor or higher for theset operations. To learn more, see the authorization guidance forSet Blob Properties (REST API),Get Blob Properties (REST API),Set Blob Metadata (REST API), orGet Blob Metadata (REST API).

Create a client object

To connect an app to Blob Storage, create an instance ofBlobServiceClient.

The following example usesBlobServiceClientBuilder to build aBlobServiceClient object usingDefaultAzureCredential, and shows how to create container and blob clients, if needed:

// Azure SDK client builders accept the credential as a parameter// TODO: Replace <storage-account-name> with your actual storage account nameBlobServiceClient blobServiceClient = new BlobServiceClientBuilder()        .endpoint("https://<storage-account-name>.blob.core.windows.net/")        .credential(new DefaultAzureCredentialBuilder().build())        .buildClient();// If needed, you can create a BlobContainerClient object from the BlobServiceClientBlobContainerClient containerClient = blobServiceClient        .getBlobContainerClient("<container-name>");// If needed, you can create a BlobClient object from the BlobContainerClientBlobClient blobClient = containerClient        .getBlobClient("<blob-name>");

To learn more about creating and managing client objects, seeCreate and manage client objects that interact with data resources.

About properties and metadata

• System properties: System properties exist on each Blob storage resource. Some of them can be read or set, while others are read-only. Under the covers, some system properties correspond to certain standard HTTP headers. The Azure Storage client library for Java maintains these properties for you.

• User-defined metadata: User-defined metadata consists of one or more name-value pairs that you specify for a Blob storage resource. You can use metadata to store additional values with the resource. Metadata values are for your own purposes only, and don't affect how the resource behaves.

  Metadata name/value pairs are valid HTTP headers and should adhere to all restrictions governing HTTP headers. For more information about metadata naming requirements, seeMetadata names.

Set and retrieve properties

To set properties on a blob, use the following method:

• setHTTPHeaders

The following code example sets theContentType andContentLanguage system properties on a blob.

Any properties not explicitly set are cleared. The following code example first gets the existing properties on the blob, then uses them to populate the headers that aren't being updated.

public void setBlobProperties(BlobClient blobClient) {    BlobProperties properties = blobClient.getProperties();    // Set the ContentLanguage and ContentType headers, and populate the remaining    // headers from the existing properties    BlobHttpHeaders blobHeaders = new BlobHttpHeaders()            .setContentLanguage("en-us")            .setContentType("text/plain")            .setCacheControl(properties.getCacheControl())            .setContentDisposition(properties.getContentDisposition())            .setContentEncoding(properties.getContentEncoding())            .setContentMd5(properties.getContentMd5());    blobClient.setHttpHeaders(blobHeaders);    System.out.println("Set HTTP headers completed");}

To retrieve properties on a blob, use the following method:

• getProperties

The following code example gets a blob's system properties and displays some of the values:

public void getBlobProperties(BlobClient blobClient) {    BlobProperties properties = blobClient.getProperties();    System.out.printf("BlobType: %s%n", properties.getBlobType());    System.out.printf("BlobSize: %d%n", properties.getBlobSize());    System.out.printf("ContentLanguage: %s%n", properties.getContentLanguage());    System.out.printf("ContentType: %s%n", properties.getContentType());}

Set and retrieve metadata

You can specify metadata as one or more name-value pairs on a blob or container resource. To set metadata, send aMap object containing name-value pairs using the following method:

• setMetadata

The following code example sets metadata on a blob:

public void addBlobMetadata(BlobClient blobClient) {    Map<String, String> metadata = new HashMap<String, String>();    metadata.put("docType", "text");    metadata.put("category", "reference");    try {        blobClient.setMetadata(metadata);        System.out.printf("Set metadata completed %n");    } catch (UnsupportedOperationException error) {        System.out.printf("Failure while setting metadata %n");    }}

To retrieve metadata, call thegetProperties method on your blob to populate the metadata collection, then read the values, as shown in the example below. ThegetProperties method retrieves blob properties and metadata by calling both theGet Blob Properties operation and theGet Blob Metadata operation.

The following code example reads metadata on a blob and prints each key/value pair:

public void readBlobMetadata(BlobClient blobClient) {    // Get blob properties and metadata    BlobProperties properties = blobClient.getProperties();    System.out.printf("Blob metadata: %n");    properties.getMetadata().entrySet().forEach(metadataItem -> {        System.out.printf(" %s = %s%n", metadataItem.getKey(), metadataItem.getValue());    });}

Resources

To learn more about how to manage system properties and user-defined metadata using the Azure Blob Storage client library for Java, see the following resources.

Code samples

• View code samples from this article (GitHub)

REST API operations

The Azure SDK for Java contains libraries that build on top of the Azure REST API, allowing you to interact with REST API operations through familiar Java paradigms. The client library methods for managing system properties and user-defined metadata use the following REST API operations:

• Set Blob Properties (REST API)
• Get Blob Properties (REST API)
• Set Blob Metadata (REST API)
• Get Blob Metadata (REST API)

Client library resources

• Client library reference documentation
• Client library source code
• Package (Maven)

Related content

• This article is part of the Blob Storage developer guide for Java. To learn more, see the full list of developer guide articles atBuild your Java app.