Azure SDK for Java Reference Documentation

Current version is 7.11.0, click here for the index

Azure Service Bus client library for Java

Microsoft Azure Service Bus is a fully managed enterprise integration message broker. Service Bus can decouple applications and services. Service Bus offers a reliable and secure platform for asynchronous transfer of data and state. Data is transferred between different applications and services using messages. If you would like to know more about Azure Service Bus, you may wish to review: What is Service Bus

The Azure Service Bus client library allows for sending and receiving of Azure Service Bus messages and may be used to: - Transfer business data, such as sales or purchase orders, journals, or inventory movements. - Decouple applications to improve reliability and scalability of applications and services. Clients and services don't have to be online at the same time. - Enable 1:n relationships between publishers and subscribers. - Implement workflows that require message ordering or message deferral.

Source code | API reference documentation | Product documentation | Samples | Package (Maven)

Getting started

Prerequisites

To quickly create the needed Service Bus resources in Azure and to receive a connection string for them, you can deploy our sample template by clicking:

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 {bomversionto_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.

<dependencies>
  <dependency>
    <groupId>com.azure</groupId>
    <artifactId>azure-messaging-servicebus</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-servicebus</artifactId>
    <version>7.11.0</version>
</dependency>

Authenticate the client

For the Service Bus client library to interact with Service Bus, it will need to understand how to connect and authorize with it.

Create Service Bus clients using a connection string

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

Both the asynchronous and synchronous Service Bus sender and receiver clients are instantiated using ServiceBusClientBuilder. The snippets below create a synchronous Service Bus sender and an asynchronous receiver, respectively.

ServiceBusSenderClient sender = new ServiceBusClientBuilder()
    .connectionString("<< CONNECTION STRING FOR THE SERVICE BUS NAMESPACE >>")
    .sender()
    .queueName("<< QUEUE NAME >>")
    .buildClient();

ServiceBusReceiverAsyncClient receiver = new ServiceBusClientBuilder()
    .connectionString("<< CONNECTION STRING FOR THE SERVICE BUS NAMESPACE >>")
    .receiver()
    .topicName("<< TOPIC NAME >>")
    .subscriptionName("<< SUBSCRIPTION NAME >>")
    .buildAsyncClient();

Create a Service Bus client using Microsoft Identity platform (formerly Azure Active Directory)

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

<dependency>
    <groupId>com.azure</groupId>
    <artifactId>azure-identity</artifactId>
    <version>1.5.4</version>
</dependency>
  • Known Issue: The pom.xml file should list azure-messaging-servicebus before azure-identity client libraries. This issue is resolved with azure-identity:1.2.1. Check here for more details.

The implemented ways to request a credential are 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 Service Bus.

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 Service Bus, please refer to the associated documentation.

Use the returned token credential to authenticate the client:

TokenCredential credential = new DefaultAzureCredentialBuilder()
    .build();
ServiceBusReceiverAsyncClient receiver = new ServiceBusClientBuilder()
    .credential("<<fully-qualified-namespace>>", credential)
    .receiver()
    .queueName("<<queue-name>>")
    .buildAsyncClient();

Key concepts

You can interact with the primary resource types within a Service Bus Namespace, of which multiple can exist and on which actual message transmission takes place. The namespace often serves as an application container:

  • A queue allows for the sending and receiving of messages, ordered first-in-first-out. It is often used for point-to-point communication.
  • A topic is better suited to publisher and subscriber scenarios. A topic publishes messages to subscriptions, of which, multiple can exist simultaneously.
  • A subscription receives messages from a topic. Each subscription is independent and receives a copy of the message sent to the topic.

Service Bus Clients

The builder ServiceBusClientBuilder is used to create all the Service Bus clients.

Examples

You'll need to create an asynchronous ServiceBusSenderAsyncClient or a synchronous ServiceBusSenderClient to send messages. Each sender can send messages to either a queue or a topic.

The snippet below creates a synchronous ServiceBusSenderClient to publish a message to a queue.

ServiceBusSenderClient sender = new ServiceBusClientBuilder()
    .connectionString("<< CONNECTION STRING FOR THE SERVICE BUS NAMESPACE >>")
    .sender()
    .queueName("<< QUEUE NAME >>")
    .buildClient();
List<ServiceBusMessage> messages = Arrays.asList(
    new ServiceBusMessage("Hello world").setMessageId("1"),
    new ServiceBusMessage("Bonjour").setMessageId("2"));

sender.sendMessages(messages);

// When you are done using the sender, dispose of it.
sender.close();

Receive messages

To receive messages, you will need to create a ServiceBusProcessorClient with callbacks for incoming messages and any error that occurs in the process. You can then start and stop the client as required.

By default, the autoComplete feature is enabled on the processor client which means that after executing your callback for the message, the client will complete the message i.e. remove it from the queue/subscription. If your callback throws an error, then the client will abandon the message i.e. make it available to be received again. You can disable this feature when creating the processor client.

// Sample code that processes a single message
Consumer<ServiceBusReceivedMessageContext> processMessage = messageContext -> {
    try {
        System.out.println(messageContext.getMessage().getMessageId());
        // other message processing code
        messageContext.complete();
    } catch (Exception ex) {
        messageContext.abandon();
    }
};

// Sample code that gets called if there's an error
Consumer<ServiceBusErrorContext> processError = errorContext -> {
    System.err.println("Error occurred while receiving message: " + errorContext.getException());
};

// create the processor client via the builder and its sub-builder
ServiceBusProcessorClient processorClient = new ServiceBusClientBuilder()
                                .connectionString("<< CONNECTION STRING FOR THE SERVICE BUS NAMESPACE >>")
                                .processor()
                                .queueName("<< QUEUE NAME >>")
                                .processMessage(processMessage)
                                .processError(processError)
                                .disableAutoComplete()
                                .buildProcessorClient();

// Starts the processor in the background and returns immediately
processorClient.start();

There are four ways of settling messages using the methods on the message context passed to your callback. - Complete - causes the message to be deleted from the queue or topic. - Abandon - releases the receiver's lock on the message allowing for the message to be received by other receivers. - Defer - defers the message from being received by normal means. In order to receive deferred messages, the sequence number of the message needs to be retained. - Dead-letter - moves the message to the dead-letter queue. This will prevent the message from being received again. In order to receive messages from the dead-letter queue, a receiver scoped to the dead-letter queue is needed.

Send and receive from session enabled queues or topics

Using sessions requires you to create a session enabled queue or subscription. You can read more about how to configure this in "Message sessions".

Azure Service Bus sessions enable joint and ordered handling of unbounded sequences of related messages. Sessions can be used in first in, first out (FIFO) and request-response patterns. Any sender can create a session when submitting messages into a topic or queue by setting the ServiceBusMessage.setSessionId(String) property to some application-defined identifier that is unique to the session.

Unlike non-session-enabled queues or subscriptions, only a single receiver can read from a session at any time. When a receiver fetches a session, Service Bus locks the session for that receiver, and it has exclusive access to messages in that session.

Send a message to a session

Create a ServiceBusSenderClient for a session enabled queue or topic subscription. Setting ServiceBusMessage.setSessionId(String) on a ServiceBusMessage will publish the message to that session. If the session does not exist, it is created.

// Setting sessionId publishes that message to a specific session, in this case, "greeting".
ServiceBusMessage message = new ServiceBusMessage("Hello world")
    .setSessionId("greetings");

sender.sendMessage(message);

Receive messages from a session

Receiving messages from sessions is similar to receiving messages from a non session enabled queue or subscription. The difference is in the builder and the class you use.

In non-session case, you would use the sub builder processor(). In case of sessions, you would use the sub builder sessionProcessor(). Both sub builders will create an instance of ServiceBusProcessorClient configured to work on a session or a non-session Service Bus entity. In the case of the session processor, you can pass the maximum number of sessions you want the processor to process concurrently as well.

Create a dead-letter queue Receiver

Azure Service Bus queues and topic subscriptions provide a secondary sub-queue, called a dead-letter queue (DLQ). The dead-letter queue doesn't need to be explicitly created and can't be deleted or otherwise managed independent of the main entity. For session enabled or non-session queue or topic subscriptions, the dead-letter receiver can be created the same way as shown below. Learn more about dead-letter queue here.

ServiceBusReceiverClient receiver = new ServiceBusClientBuilder()
    .connectionString("<< CONNECTION STRING FOR THE SERVICE BUS NAMESPACE >>")
    .receiver() // Use this for session or non-session enabled queue or topic/subscriptions
    .topicName("<< TOPIC NAME >>")
    .subscriptionName("<< SUBSCRIPTION NAME >>")
    .subQueue(SubQueue.DEAD_LETTER_QUEUE)
    .buildClient();

Sharing of connection between clients

The creation of physical connection to Service Bus requires resources. An application should share the connection between clients which can be achieved by sharing the top level builder as shown below.

// Create shared builder.
ServiceBusClientBuilder sharedConnectionBuilder = new ServiceBusClientBuilder()
    .connectionString("<< CONNECTION STRING FOR THE SERVICE BUS NAMESPACE >>");
// Create receiver and sender which will share the connection.
ServiceBusReceiverClient receiver = sharedConnectionBuilder
    .receiver()
    .queueName("<< QUEUE NAME >>")
    .buildClient();
ServiceBusSenderClient sender = sharedConnectionBuilder
    .sender()
    .queueName("<< QUEUE NAME >>")
    .buildClient();

When to use 'ServiceBusProcessorClient'.

When to use 'ServiceBusProcessorClient', 'ServiceBusReceiverClient' or ServiceBusReceiverAsyncClient? The processor is built using 'ServiceBusReceiverAsyncClient', it provides a convenient way of receiving messages with default auto complete and auto-renew of message locks in 'PEEK_LOCK' mode. The processor is appropriate where the applications have not made complete move to async receiver client and want to process message in synchronous mode. The processor receives messages forever because it recovers from the network errors internally. 'ServiceBusProcessorClient:processMessage()' function call is made for each message. Alternatively, You can also use 'ServiceBusReceiverClient', it is a lower level client and provides a wider range of APIs. If async processing is suitable for your application, you can use 'ServiceBusReceiverAsyncClient'.

Troubleshooting

Enable client logging

Azure SDK for Java offers a consistent logging story to help aid in troubleshooting application errors and expedite their resolution. The logs produced will capture the flow of an application before reaching the terminal state to help locate the root issue. View the logging wiki for guidance about enabling logging.

Enable AMQP transport logging

If enabling client logging is not enough to diagnose your issues. You can enable logging to a file in the underlying AMQP library, Qpid Proton-J. Qpid Proton-J uses java.util.logging. You can enable logging by create a configuration file with the contents below. Or set proton.trace.level=ALL and whichever configuration options you want for the java.util.logging.Handler implementation. Implementation classes and their options can be found in Java 8 SDK javadoc.

To trace the AMQP transport frames, set the environment variable: PN_TRACE_FRM=1.

Sample "logging.properties" file

The configuration file below logs trace output from proton-j to the file "proton-trace.log".

handlers=java.util.logging.FileHandler
.level=OFF
proton.trace.level=ALL
java.util.logging.FileHandler.level=ALL
java.util.logging.FileHandler.pattern=proton-trace.log
java.util.logging.FileHandler.formatter=java.util.logging.SimpleFormatter
java.util.logging.SimpleFormatter.format=[%1$tF %1$tr] %3$s %4$s: %5$s %n

Common exceptions

AMQP exception

This is a general exception for AMQP related failures, which includes the AMQP errors as ErrorCondition and the context that caused this exception as AmqpErrorContext. isTransient is a boolean indicating if the exception is a transient error or not. If a transient AMQP exception occurs, the client library retries the operation as many times as the AmqpRetryOptions allows. Afterwords, the operation fails and an exception is propagated back to the user.

AmqpErrorCondition contains error conditions common to the AMQP protocol and used by Azure services. When an AMQP exception is thrown, examining the error condition field can inform developers as to why the AMQP exception occurred and if possible, how to mitigate this exception. A list of all the AMQP exceptions can be found in OASIS AMQP Version 1.0 Transport Errors.

The recommended way to solve the specific exception the AMQP exception represents is to follow the Service Bus Messaging Exceptions guidance.

Understanding the APIs behavior

The document here provides insights into the expected behavior of synchronous receiveMessages API when using it to obtain more than one message (a.k.a. implicit prefetching).

Next steps

Beyond those discussed, the Azure Service Bus client library offers support for many additional scenarios to help take advantage of the full feature set of the Azure Service Bus service. In order to help explore some of these scenarios, the following set of sample is available here.

Contributing

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

Packages
Package
Description
com.azure.messaging.servicebus
Package containing classes for creating ServiceBusSenderAsyncClient, ServiceBusProcessorClient, and ServiceBusReceiverAsyncClient to perform operations on Azure Service Bus.
com.azure.messaging.servicebus.administration
Package containing classes managing resources in Azure Service Bus.
com.azure.messaging.servicebus.administration.models
Package containing classes models for ServiceBusAdministrationClient and ServiceBusAdministrationAsyncClient used for managing Queues, Topics, and Subscriptions.
com.azure.messaging.servicebus.models
Model classes for interacting with Azure Service Bus.