Azure Event Hubs client library for Java - version 5.19.1

  • Article

Azure Event Hubs is a highly scalable publish-subscribe service that can ingest millions of events per second and stream them to multiple consumers. This lets you process and analyze the massive amounts of data produced by your connected devices and applications. Once Event Hubs has collected the data, you can retrieve, transform, and store it by using any real-time analytics provider or with batching/storage adapters. If you would like to know more about Azure Event Hubs, you may wish to review: What is Event Hubs?

The Azure Event Hubs client library allows for publishing and consuming of Azure Event Hubs events and may be used to:

  • Emit telemetry about your application for business intelligence and diagnostic purposes.
  • Publish facts about the state of your application which interested parties may observe and use as a trigger for taking action.
  • Observe interesting operations and interactions happening within your business or other ecosystem, allowing loosely coupled systems to interact without the need to bind them together.
  • Receive events from one or more publishers, transform them to better meet the needs of your ecosystem, then publish the transformed events to a new stream for consumers to observe.

Source code | API reference documentation | Product documentation | Samples | Troubleshooting

Table of contents

Getting started

Prerequisites

Include the package

Include the BOM file

Please include the azure-sdk-bom to your project to take dependency on the General Availability (GA) version of the library. In the following snippet, replace the {bom_version_to_target} placeholder with the version number. 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>

and then include the direct dependency in the dependencies section without the version tag as shown below.

<dependencies>
  <dependency>
    <groupId>com.azure</groupId>
    <artifactId>azure-messaging-eventhubs</artifactId>
  </dependency>
</dependencies>

Include direct dependency

If you want to take dependency on a particular version of the library that is not present in the BOM, add the direct dependency to your project as follows.

<dependency>
    <groupId>com.azure</groupId>
    <artifactId>azure-messaging-eventhubs</artifactId>
    <version>5.19.1</version>
</dependency>

Authenticate the client

For the Event Hubs client library to interact with an Event Hub, it will need to understand how to connect and authorize with it.

Create an Event Hub producer using a connection string

The easiest means for doing so is to use a connection string, which is created automatically when creating an Event Hubs namespace. If you aren't familiar with shared access policies in Azure, you may wish to follow the step-by-step guide to get an Event Hubs connection string.

Both the asynchronous and synchronous Event Hub producer and consumer clients can be created using EventHubClientBuilder. Invoking build*Client() creates a synchronous producer or consumer while build*AsyncClient() creates its asynchronous counterpart.

The snippet below creates a synchronous Event Hub producer.

TokenCredential credential = new DefaultAzureCredentialBuilder().build();

// "<<fully-qualified-namespace>>" will look similar to "{your-namespace}.servicebus.windows.net"
// "<<event-hub-name>>" will be the name of the Event Hub instance you created inside the Event Hubs namespace.
EventHubProducerClient producer = new EventHubClientBuilder()
    .credential("<<fully-qualified-namespace>>", "<<event-hub-name>>",
        credential)
    .buildProducerClient();

Create an Event Hub client using Microsoft identity platform (formerly Azure Active Directory)

Azure SDK for Java supports an Azure Identity package, making it easy to get credentials from Microsoft identity platform. First, add the package:

<dependency>
    <groupId>com.azure</groupId>
    <artifactId>azure-identity</artifactId>
    <version>1.13.3</version>
</dependency>

All the implemented ways to request a credential can be found under the com.azure.identity.credential package. The sample below shows how to use an Azure Active Directory (AAD) application client secret to authorize with Azure Event Hubs.

Authorizing with DefaultAzureCredential

Authorization is easiest using DefaultAzureCredential. It finds the best credential to use in its running environment. For more information about using Azure Active Directory authorization with Event Hubs, please refer to the associated documentation.

TokenCredential credential = new DefaultAzureCredentialBuilder().build();

// "<<fully-qualified-namespace>>" will look similar to "{your-namespace}.servicebus.windows.net"
// "<<event-hub-name>>" will be the name of the Event Hub instance you created inside the Event Hubs namespace.
EventHubProducerClient producer = new EventHubClientBuilder()
    .credential("<<fully-qualified-namespace>>", "<<event-hub-name>>",
        credential)
    .buildProducerClient();

Key concepts

  • An Event Hub producer is a source of telemetry data, diagnostics information, usage logs, or other log data, as part of an embedded device solution, a mobile device application, a game title running on a console or other device, some client or server based business solution, or a website.

  • An Event Hub consumer picks up such information from the Event Hub and processes it. Processing may involve aggregation, complex computation, and filtering. Processing may also involve distribution or storage of the information in a raw or transformed fashion. Event Hub consumers are often robust and high-scale platform infrastructure parts with built-in analytics capabilities, like Azure Stream Analytics, Apache Spark, or Apache Storm.

  • A partition is an ordered sequence of events that is held in an Event Hub. Azure Event Hubs provides message streaming through a partitioned consumer pattern in which each consumer only reads a specific subset, or partition, of the message stream. As newer events arrive, they are added to the end of this sequence. The number of partitions is specified at the time an Event Hub is created and cannot be changed.

  • A consumer group is a view of an entire Event Hub. Consumer groups enable multiple consuming applications to each have a separate view of the event stream, and to read the stream independently at their own pace and from their own position. There can be at most 5 concurrent readers on a partition per consumer group; however it is recommended that there is only one active consumer for a given partition and consumer group pairing. Each active reader receives the events from its partition; if there are multiple readers on the same partition, then they will receive duplicate events.

For more concepts and deeper discussion, see: Event Hubs Features. Also, the concepts for AMQP are well documented in OASIS Advanced Messaging Queuing Protocol (AMQP) Version 1.0.

Examples

Publish events to an Event Hub

To publish events, you'll need to create an asynchronous EventHubProducerAsyncClient or a synchronous EventHubProducerClient. Each producer can send events to either, a specific partition, or allow the Event Hubs service to decide which partition events should be published to. It is recommended to use automatic routing when the publishing of events needs to be highly available or when event data should be distributed evenly among the partitions.

Create an Event Hub producer and publish events

Developers can create a producer using EventHubClientBuilder and calling buildProducer*Client(). Specifying CreateBatchOptions.setPartitionId(String) will send events to a specific partition. If partitionId is not specified, events are automatically routed to a partition. Specifying CreateBatchOptions.setPartitionKey(String) will tell Event Hubs service to hash the events and send them to the same partition.

The snippet below creates a synchronous producer and sends events to any partition, allowing Event Hubs service to route the event to an available partition.

TokenCredential credential = new DefaultAzureCredentialBuilder().build();

EventHubProducerClient producer = new EventHubClientBuilder()
    .credential("<<fully-qualified-namespace>>", "<<event-hub-name>>",
        credential)
    .buildProducerClient();

List<EventData> allEvents = Arrays.asList(new EventData("Foo"), new EventData("Bar"));
EventDataBatch eventDataBatch = producer.createBatch();

for (EventData eventData : allEvents) {
    if (!eventDataBatch.tryAdd(eventData)) {
        producer.send(eventDataBatch);
        eventDataBatch = producer.createBatch();

        // Try to add that event that couldn't fit before.
        if (!eventDataBatch.tryAdd(eventData)) {
            throw new IllegalArgumentException("Event is too large for an empty batch. Max size: "
                + eventDataBatch.getMaxSizeInBytes());
        }
    }
}

// send the last batch of remaining events
if (eventDataBatch.getCount() > 0) {
    producer.send(eventDataBatch);
}

// Clients are expected to be long-lived objects.
// Dispose of the producer to close any underlying resources when we are finished with it.
producer.close();

Note that EventDataBatch.tryAdd(EventData) is not thread-safe. Please make sure to synchronize the method access when using multiple threads to add events.

Publish events using partition identifier

Many Event Hub operations take place within the scope of a specific partition. Any client can call getPartitionIds() or getEventHubProperties() to get the partition ids and metadata about in their Event Hub instance.

TokenCredential credential = new DefaultAzureCredentialBuilder().build();

EventHubProducerClient producer = new EventHubClientBuilder()
    .credential("<<fully-qualified-namespace>>", "<<event-hub-name>>",
        credential)
    .buildProducerClient();

// Creating a batch with partitionId set will route all events in that batch to partition `0`.
CreateBatchOptions options = new CreateBatchOptions().setPartitionId("0");
EventDataBatch batch = producer.createBatch(options);

// Add events to batch and when you want to send the batch, send it using the producer.
producer.send(batch);

Publish events using partition key

When a set of events are not associated with any specific partition, it may be desirable to request that the Event Hubs service keep different events or batches of events together on the same partition. This can be accomplished by setting a partition key when publishing the events. In the scenario below, all the events are related to cities, so they are sent with the partition key set to "cities".

TokenCredential credential = new DefaultAzureCredentialBuilder().build();

EventHubProducerClient producer = new EventHubClientBuilder()
    .credential("<<fully-qualified-namespace>>", "<<event-hub-name>>",
        credential)
    .buildProducerClient();

List<EventData> events = Arrays.asList(new EventData("Melbourne"), new EventData("London"),
    new EventData("New York"));

SendOptions sendOptions = new SendOptions().setPartitionKey("cities");
producer.send(events, sendOptions);

Consume events from an Event Hub partition

To consume events, create an EventHubConsumerAsyncClient or EventHubConsumerClient for a specific consumer group. In addition, a consumer needs to specify where in the event stream to begin receiving events.

Consume events with EventHubConsumerAsyncClient

In the snippet below, we create an asynchronous consumer that receives events from partitionId and only listens to the newest events that get pushed to the partition. Developers can begin receiving events from multiple partitions using the same EventHubConsumerAsyncClient by calling receiveFromPartition(String, EventPosition) with another partition id.

EventHubConsumerAsyncClient consumer = new EventHubClientBuilder()
    .credential("<<fully-qualified-namespace>>", "<<event-hub-name>>",
        new DefaultAzureCredentialBuilder().build())
    .consumerGroup(EventHubClientBuilder.DEFAULT_CONSUMER_GROUP_NAME)
    .buildAsyncConsumerClient();

// Obtain partitionId from EventHubConsumerAsyncClient.getPartitionIds()
String partitionId = "0";
EventPosition startingPosition = EventPosition.latest();

// Keep a reference to `subscription`. When the program is finished receiving events, call
// subscription.dispose(). This will stop fetching events from the Event Hub.
//
// NOTE: This is a non-blocking call and will move to the next line of code after setting up the async
// operation.  If the program ends after this, or the class is immediately disposed, no events will be
// received.
Disposable subscription = consumer.receiveFromPartition(partitionId, startingPosition)
    .subscribe(partitionEvent -> {
        PartitionContext partitionContext = partitionEvent.getPartitionContext();
        EventData event = partitionEvent.getData();

        System.out.printf("Received event from partition '%s'%n", partitionContext.getPartitionId());
        System.out.printf("Contents of event as string: '%s'%n", event.getBodyAsString());
    }, error -> {
        // This is a terminal signal.  No more events will be received from the same Flux object.
        System.err.print("An error occurred:" + error);
    }, () -> {
        // This is a terminal signal.  No more events will be received from the same Flux object.
        System.out.print("Stream has ended.");
    });

Consume events with EventHubConsumerClient

Developers can create a synchronous consumer that returns events in batches using an EventHubConsumerClient. In the snippet below, a consumer is created that starts reading events from the beginning of the partition's event stream.

TokenCredential credential = new DefaultAzureCredentialBuilder().build();

// "<<fully-qualified-namespace>>" will look similar to "{your-namespace}.servicebus.windows.net"
// "<<event-hub-name>>" will be the name of the Event Hub instance you created inside the Event Hubs namespace.
EventHubConsumerClient consumer = new EventHubClientBuilder()
    .credential("<<fully-qualified-namespace>>", "<<event-hub-name>>",
        credential)
    .consumerGroup(EventHubClientBuilder.DEFAULT_CONSUMER_GROUP_NAME)
    .buildConsumerClient();

Instant twelveHoursAgo = Instant.now().minus(Duration.ofHours(12));
EventPosition startingPosition = EventPosition.fromEnqueuedTime(twelveHoursAgo);
String partitionId = "0";

// Reads events from partition '0' and returns the first 100 received or until the 30 seconds has elapsed.
IterableStream<PartitionEvent> events = consumer.receiveFromPartition(partitionId, 100,
    startingPosition, Duration.ofSeconds(30));

Long lastSequenceNumber = -1L;
for (PartitionEvent partitionEvent : events) {
    // For each event, perform some sort of processing.
    System.out.print("Event received: " + partitionEvent.getData().getSequenceNumber());
    lastSequenceNumber = partitionEvent.getData().getSequenceNumber();
}

// Figure out what the next EventPosition to receive from is based on last event we processed in the stream.
// If lastSequenceNumber is -1L, then we didn't see any events the first time we fetched events from the
// partition.
if (lastSequenceNumber != -1L) {
    EventPosition nextPosition = EventPosition.fromSequenceNumber(lastSequenceNumber, false);

    // Gets the next set of events from partition '0' to consume and process.
    IterableStream<PartitionEvent> nextEvents = consumer.receiveFromPartition(partitionId, 100,
        nextPosition, Duration.ofSeconds(30));
}

Consume events using an EventProcessorClient

To consume events for all partitions of an Event Hub, you can create an EventProcessorClient for a specific consumer group.

The EventProcessorClient will delegate processing of events to a callback function that you provide, allowing you to focus on the logic needed to provide value while the processor holds responsibility for managing the underlying consumer operations.

In our example, we will focus on building the EventProcessorClient, use the SampleCheckpointStore available in samples, and a callback function that processes events received from the Event Hub and writes to console. For production applications, it's recommended to use a durable store like Checkpoint Store with Azure Storage Blobs.

TokenCredential credential = new DefaultAzureCredentialBuilder().build();

// "<<fully-qualified-namespace>>" will look similar to "{your-namespace}.servicebus.windows.net"
// "<<event-hub-name>>" will be the name of the Event Hub instance you created inside the Event Hubs namespace.
EventProcessorClient eventProcessorClient = new EventProcessorClientBuilder()
    .consumerGroup("<< CONSUMER GROUP NAME >>")
    .credential("<<fully-qualified-namespace>>", "<<event-hub-name>>",
        credential)
    .checkpointStore(new SampleCheckpointStore())
    .processEvent(eventContext -> {
        System.out.printf("Partition id = %s and sequence number of event = %s%n",
            eventContext.getPartitionContext().getPartitionId(),
            eventContext.getEventData().getSequenceNumber());
    })
    .processError(errorContext -> {
        System.out.printf("Error occurred in partition processor for partition %s, %s%n",
            errorContext.getPartitionContext().getPartitionId(),
            errorContext.getThrowable());
    })
    .buildEventProcessorClient();

Troubleshooting

See TROUBLESHOOTING.md.

Next steps

Beyond those discussed, the Azure Event Hubs client library offers support for many other scenarios to take advantage of the full feature set of the Azure Event Hubs service. To explore some of these scenarios, check out the samples README.

Contributing

If you would like to become an active contributor to this project please refer to our Contribution Guidelines for more information.

Impressions