Manage blob properties and metadata with Java
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 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 blob 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. 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, see Metadata names.
Note
Blob index tags also provide the ability to store arbitrary user-defined key/value attributes alongside an Azure Blob storage resource. While similar to metadata, only blob index tags are automatically indexed and made searchable by the native blob service. Metadata cannot be indexed and queried unless you utilize a separate service such as Azure Search.
To learn more about this feature, see Manage and find data on Azure Blob storage with blob index.
Set and retrieve properties
To set properties on a blob, use the following method:
The following code example sets the ContentType
and ContentLanguage
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:
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 a Map object containing name-value pairs using the following method:
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 the getProperties method on your blob to populate the metadata collection, then read the values, as shown in the example below. The getProperties
method retrieves blob properties and metadata by calling both the Get Blob Properties operation and the Get 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.
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)
Code samples
Client library resources
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