Manage container properties and metadata with Java

Article
08/02/2023

Blob containers support system properties and user-defined metadata, in addition to the data they contain. This article shows how to manage system properties and user-defined metadata with the Azure Storage client library for Java.

Prerequisites

This article assumes you already have a project set up to work with the Azure Blob Storage client library for Java. To learn about setting up your project, including package installation, adding import directives, and creating an authorized client object, see Get Started with Azure Storage and Java.
The authorization mechanism must have permissions to work with container properties or metadata. To learn more, see the authorization guidance for the following REST API operations:

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. Behind the scenes, 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, see Metadata names.

Retrieve container properties

To retrieve container properties, use the following method:

getProperties

The following code example fetches a container's system properties and writes the property values to a console window:

public void getContainerProperties(BlobContainerClient blobContainerClient) {
    BlobContainerProperties properties = blobContainerClient.getProperties();
    System.out.printf("Public Access Type: %s, Legal Hold? %b, Immutable? %b%n",
            properties.getBlobPublicAccess(),
            properties.hasLegalHold(),
            properties.hasImmutabilityPolicy());
}

Set and retrieve metadata

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

setMetadata

Setting container metadata overwrites all existing metadata associated with the container. It's not possible to modify an individual name-value pair.

The following code example sets metadata on a container:

public void addContainerMetadata(BlobContainerClient blobContainerClient) {
    Map<String, String> metadata = new HashMap<String, String>();
    metadata.put("docType", "text");
    metadata.put("category", "reference");

    try {
        blobContainerClient.setMetadata(metadata);
        System.out.printf("Set metadata completed %n");
    } catch (UnsupportedOperationException error) {
        System.out.printf("Failure while setting metadata %n");
    }
}

To retrieve metadata, call the following method:

getProperties

The following example reads in metadata values:

public void readContainerMetadata(BlobContainerClient blobContainerClient) {
    BlobContainerProperties properties = blobContainerClient.getProperties();

    System.out.printf("Container metadata: %n");
    properties.getMetadata().entrySet().forEach(metadataItem -> {
        System.out.printf(" %s = %s%n", metadataItem.getKey(), metadataItem.getValue());
    });
}

Resources

To learn more about setting and retrieving container properties and metadata using the Azure Blob Storage client library for Java, see the following resources.

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 setting and retrieving properties and metadata use the following REST API operations:

The getProperties method retrieves container properties and metadata by calling both the Get Blob Properties operation and the Get Blob Metadata operation.

Code samples

View code samples from this article (GitHub)