azure-docs-sdk-java/docs-ref-services/messaging-servicebus-readme-pre.md

title	keywords	author	ms.author	ms.date	ms.topic	ms.prod	ms.technology	ms.devlang	ms.service
	Azure, java, SDK, API, azure-messaging-servicebus, servicebus	maggiepint	magpint	09/12/2020	article	azure	azure	java	servicebus

Azure Service Bus client library for Java - Version 7.0.0-beta.6

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

Getting started

Prerequisites

• Java Development Kit (JDK) with version 8 or above
• Maven
• Microsoft Azure subscription
  • You can create a free account at: https://azure.microsoft.com
• Azure Service Bus instance
  • Step-by-step guide for creating a Service Bus instance using Azure Portal

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

<dependency>
    <groupId>com.azure</groupId>
    <artifactId>azure-messaging-servicebus</artifactId>
    <version>7.0.0-beta.6</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>1.0.9</version>
</dependency>

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.

• ServiceBusSenderClient A synchronous sender responsible for sending ServiceBusMessage to specific queue or topic on Azure Service Bus.
• ServiceBusSenderAsyncClient A asynchronous sender responsible for sending ServiceBusMessage to specific queue or topic on Azure Service Bus.
• ServiceBusReceiverClient A synchronous receiver responsible for receiving ServiceBusMessage from a specific queue or topic on Azure Service Bus.
• ServiceBusReceiverAsyncClient A asynchronous receiver responsible for receiving ServiceBusMessage from a specific queue or topic on Azure Service Bus.

Examples

• Send messages
• Receive messages
• Settle messages
• Send and receive from session enabled queues or topics
• Create a dead-letter queue Receiver

Send messages

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

You'll need to create an asynchronous ServiceBusReceiverAsyncClient or a synchronous ServiceBusReceiverClient to receive messages. Each receiver can consume messages from either a queue or a topic subscription.

By default, the receive mode is ReceiveMode.PEEK_LOCK. This tells the broker that the receiving client wants to manage settlement of received messages explicitly. The message is made available for the receiver to process, while held under an exclusive lock in the service so that other, competing receivers cannot see it. ServiceBusReceivedMessage.getLockedUntil() indicates when the lock expires and can be extended by the client using receiver.renewMessageLock().

Receive a batch of messages

The snippet below creates a ServiceBusReceiverClient to receive messages from a topic subscription.

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

// Receives a batch of messages when 10 messages are received or until 30 seconds have elapsed, whichever
// happens first.
IterableStream<ServiceBusReceivedMessageContext> messages = receiver.receiveMessages(10, Duration.ofSeconds(30));
messages.forEach(context -> {
    ServiceBusReceivedMessage message = context.getMessage();
    System.out.printf("Id: %s. Contents: %s%n", message.getMessageId(),
        new String(message.getBody(), StandardCharsets.UTF_8));
});

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

Receive a stream of messages

The asynchronous ServiceBusReceiverAsyncClient continuously fetches messages until the subscription is disposed.

ServiceBusReceiverAsyncClient receiver = new ServiceBusClientBuilder()
    .connectionString("<< CONNECTION STRING FOR THE SERVICE BUS NAMESPACE >>")
    .receiver()
    .queueName("<< QUEUE NAME >>")
    .buildAsyncClient();

// receive() operation continuously fetches messages until the subscription is disposed.
// The stream is infinite, and completes when the subscription or receiver is closed.
Disposable subscription = receiver.receiveMessages().subscribe(context -> {
    ServiceBusReceivedMessage message = context.getMessage();
    System.out.printf("Id: %s%n", message.getMessageId());
    System.out.printf("Contents: %s%n", new String(message.getBody(), StandardCharsets.UTF_8));
}, error -> {
        System.err.println("Error occurred while receiving messages: " + error);
    }, () -> {
        System.out.println("Finished receiving messages.");
    });

// Continue application processing. When you are finished receiving messages, dispose of the subscription.
subscription.dispose();

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

Settle messages

When a message is received, it can be settled using any of the complete(), abandon(), defer(), or deadLetter() overloads. The sample below completes a received message from synchronous ServiceBusReceiverClient.

// This fetches a batch of 10 messages or until the default operation timeout has elapsed.
receiver.receiveMessages(10).forEach(context -> {
    ServiceBusReceivedMessage message = context.getMessage();

    // Process message and then complete it.
    receiver.complete(message);
});

There are four ways of settling messages:

• 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

Receivers can fetch messages from a specific session or the first available, unlocked session.

// Creates a session-enabled receiver that gets messages from the session "greetings".
ServiceBusReceiverAsyncClient receiver = new ServiceBusClientBuilder()
    .connectionString("<< CONNECTION STRING FOR THE SERVICE BUS NAMESPACE >>")
    .sessionReceiver()
    .queueName("<< QUEUE NAME >>")
    .sessionId("greetings")
    .buildAsyncClient();

// Creates a session-enabled receiver that gets messages from the first available session.
ServiceBusReceiverAsyncClient receiver = new ServiceBusClientBuilder()
    .connectionString("<< CONNECTION STRING FOR THE SERVICE BUS NAMESPACE >>")
    .sessionReceiver()
    .queueName("<< QUEUE NAME >>")
    .buildAsyncClient();

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. Learn more about dead-letter queue here.

ServiceBusReceiverClient receiver = new ServiceBusClientBuilder()
    .connectionString("<< CONNECTION STRING FOR THE SERVICE BUS NAMESPACE >>")
    .receiver()
    .topicName("<< TOPIC NAME >>")
    .subscriptionName("<< SUBSCRIPTION NAME >>")
    .subQueue(SubQueue.DEAD_LETTER_QUEUE)
    .buildClient();

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 AmqpRetryOptons 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.

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.