Send messages to an Azure Service Bus topic and receive messages from subscriptions to the topic (Java)

In this quickstart, you write Java code using the azure-messaging-servicebus package to send messages to an Azure Service Bus topic and then receive messages from subscriptions to that topic.

Important

This quickstart uses the new azure-messaging-servicebus package. For a quickstart that uses the old azure-servicebus package, see Send and receive messages using azure-servicebus.

Prerequisites

Send messages to a topic

In this section, you'll create a Java console project, and add code to send messages to the topic you created.

Create a Java console project

Create a Java project using Eclipse or a tool of your choice.

Configure your application to use Service Bus

Add a reference to Azure Service Bus library. The Java client library for Service Bus is available in the Maven Central Repository. You can reference this library using the following dependency declaration inside your Maven project file:

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

Add code to send messages to the topic

  1. Add the following import statements at the topic of the Java file.

    import com.azure.messaging.servicebus.*;
    import com.azure.messaging.servicebus.models.*;
    import java.util.concurrent.TimeUnit;
    import java.util.function.Consumer;
    import java.util.Arrays;
    import java.util.List;
    
  2. In the class, define variables to hold connection string and topic name as shown below:

    static String connectionString = "<NAMESPACE CONNECTION STRING>";
    static String topicName = "<TOPIC NAME>";    
    static String subName = "<SUBSCRIPTION NAME>";
    

    Replace <NAMESPACE CONNECTION STRING> with the connection string to your Service Bus namespace. And, replace <TOPIC NAME> with the name of the topic.

  3. Add a method named sendMessage in the class to send one message to the topic.

        static void sendMessage()
    {
        // create a Service Bus Sender client for the queue 
        ServiceBusSenderClient senderClient = new ServiceBusClientBuilder()
                .connectionString(connectionString)
                .sender()
                .topicName(topicName)
                .buildClient();
    
        // send one message to the topic
        senderClient.sendMessage(new ServiceBusMessage("Hello, World!"));
        System.out.println("Sent a single message to the topic: " + topicName);        
    }
    
  4. Add a method named createMessages in the class to create a list of messages. Typically, you get these messages from different parts of your application. Here, we create a list of sample messages.

    static List<ServiceBusMessage> createMessages()
    {
        // create a list of messages and return it to the caller
        ServiceBusMessage[] messages = {
        		new ServiceBusMessage("First message"),
        		new ServiceBusMessage("Second message"),
        		new ServiceBusMessage("Third message")
        };
        return Arrays.asList(messages);
    }
    
  5. Add a method named sendMessageBatch method to send messages to the topic you created. This method creates a ServiceBusSenderClient for the topic, invokes the createMessages method to get the list of messages, prepares one or more batches, and sends the batches to the topic.

    static void sendMessageBatch()
    {
        // create a Service Bus Sender client for the topic 
        ServiceBusSenderClient senderClient = new ServiceBusClientBuilder()
                .connectionString(connectionString)
                .sender()
                .topicName(topicName)
                .buildClient();

        // Creates an ServiceBusMessageBatch where the ServiceBus.
        ServiceBusMessageBatch messageBatch = senderClient.createMessageBatch();        
        
    	// create a list of messages
        List<ServiceBusMessage> listOfMessages = createMessages();
        
        // We try to add as many messages as a batch can fit based on the maximum size and send to Service Bus when
        // the batch can hold no more messages. Create a new batch for next set of messages and repeat until all
        // messages are sent.        
        for (ServiceBusMessage message : listOfMessages) {
            if (messageBatch.tryAddMessage(message)) {
                continue;
            }

            // The batch is full, so we create a new batch and send the batch.
            senderClient.sendMessages(messageBatch);
            System.out.println("Sent a batch of messages to the topic: " + topicName);
            
            // create a new batch
            messageBatch = senderClient.createMessageBatch();

            // Add that message that we couldn't before.
            if (!messageBatch.tryAddMessage(message)) {
                System.err.printf("Message is too large for an empty batch. Skipping. Max size: %s.", messageBatch.getMaxSizeInBytes());
            }
        }

        if (messageBatch.getCount() > 0) {
            senderClient.sendMessages(messageBatch);
            System.out.println("Sent a batch of messages to the topic: " + topicName);
        }

        //close the client
        senderClient.close();
    }

Receive messages from a subscription

In this section, you'll add code to retrieve messages from a subscription to the topic.

  1. Add a method named receiveMessages to receive messages from the subscription. This method creates a ServiceBusProcessorClient for the subscription by specifying a handler for processing messages and another one for handling errors. Then, it starts the processor, waits for few seconds, prints the messages that are received, and then stops and closes the processor.

    // handles received messages
    static void receiveMessages() throws InterruptedException
    {
        // Consumer that processes a single message received from Service Bus
        Consumer<ServiceBusReceivedMessageContext> messageProcessor = context -> {
            ServiceBusReceivedMessage message = context.getMessage();
            System.out.println("Received message: " + message.getBody().toString() + " from the subscription: " + subName);
        };
    
        // Consumer that handles any errors that occur when receiving messages
        Consumer<Throwable> errorHandler = throwable -> {
            System.out.println("Error when receiving messages: " + throwable.getMessage());
            if (throwable instanceof ServiceBusReceiverException) {
                ServiceBusReceiverException serviceBusReceiverException = (ServiceBusReceiverException) throwable;
                System.out.println("Error source: " + serviceBusReceiverException.getErrorSource());
            }
        };
    
        // Create an instance of the processor through the ServiceBusClientBuilder
        ServiceBusProcessorClient processorClient = new ServiceBusClientBuilder()
            .connectionString(connectionString)
            .processor()
            .topicName(topicName)
            .subscriptionName(subName)
            .processMessage(messageProcessor)
            .processError(errorHandler)
            .buildProcessorClient();
    
        System.out.println("Starting the processor");
        processorClient.start();
    
        TimeUnit.SECONDS.sleep(10);
        System.out.println("Stopping and closing the processor");
        processorClient.close();    	
    }
    
  2. Update the main method to invoke sendMessage, sendMessageBatch, and receiveMessages methods and to throw InterruptedException.

    public static void main(String[] args) throws InterruptedException {    	
    	sendMessage();
    	sendMessageBatch();
    	receiveMessages();
    }   
    

Run the app

Run the program to see the output similar to the following output:

Sent a batch of messages to the topic: mytopic
Starting the processor
Received message: First message from the subscription: mysub
Received message: Second message from the subscription: mysub
Received message: Third message from the subscription: mysub
Stopping and closing the processor

On the Overview page for the Service Bus namespace in the Azure portal, you can see incoming and outgoing message count. You may need to wait for a minute or so and then refresh the page to see the latest values.

Incoming and outgoing message count

Switch to the Topics tab in the middle-bottom pane, and select the topic to see the Service Bus Topic page for your topic. On this page, you should see four incoming and four outgoing messages in the Messages chart.

Incoming and outgoing messages

If you comment out the receiveMessages call in the main method and run the app again, on the Service Bus Topic page, you see 8 incoming messages (4 new) but four outgoing messages.

Updated topic page

On this page, if you select a subscription, you get to the Service Bus Subscription page. You can see the active message count, dead-letter message count, and more on this page. In this example, there are four active messages that haven't been received by a receiver yet.

Active message count

Next steps

See the following documentation and samples: