Spring Boot RabbitMQ Topic Exchange Example

In this tutorial, we’ll go through the step by step guide to implement messaging using RabbitMQ in a Spring Boot Application and will see how to publish and consume messages to Topic Exchange and queues using RabbitMQ.

When the producer publishes messages to RabbitMQ server, they are not published directly to a queue, instead first they goes to exchange. An exchange is in charge of routing messages to different queues using bindings and routing keys. A binding connects a queue and an exchange.

There are 5 types of exchanges

1.Direct Exchange

2.Topic Exchange

3.Fanout Exchange

4.Headers Exchange

5.Default Exchange

This is the second post in this series.

First part covers about Direct Exchange.

Third part covers about Fanout Exchange

Fourth part covers about Headers Exchange

In this blog post I will show you how to create and use Topic Exchange in Spring Boot applications.

Topic Exchange

Topic exchanges route messages to queues based on wildcard matches between the routing key and the routing pattern, which is specified by the queue binding. Messages are routed to one or many queues based on a matching between a message routing key and matching pattern.

The topic exchange type is often used to implement various publish/subscribe pattern variations. Topic exchanges are commonly used for the multicast routing of messages.

Topic exchanges have a very broad set of use cases. Whenever a problem involves multiple consumers/applications that selectively choose which type of messages they want to receive, the use of topic exchanges should be considered.

The routing key must be a list of words, delimited by a period (.).

routing key can contain 2 special keys * or #

# – indicates a match of zero or more words

* – matches a word in a specific position of the routing key

Examples are report.monthly and report.*.weekly which in this case identifies reports that are set up for a bank.

The routing patterns may contain an asterisk (“*”) to match a word in a specific position of the routing key (e.g., a routing pattern of “report.*.*.weekly” only match routing keys where the first word is “report” and the fourth word is “weekly”).

A pound symbol (“#”) indicates a match of zero or more words (e.g., a routing pattern of “reports.monthly.#” matches any routing keys beginning with “reports.monthly”).

If producer sends a message with routing key “report.monthly” , it will match the routing key of

  • report.monthly.#
  • report.#

So message is routed to Queue A and Queue C

If producer sends a message with routing key “report.personalaccount.weekly” , it will match the routing key of

  • report.*.weekly
  • report.#

So message is routed to Queue B and Queue C

Setting Up Project

Go to Spring Initializr and add the following starter dependencies to a project.

  • Spring Web
  • Spring for RabbitMQ

Change the Name to “springboot-rabbitmq-producer” and then click on “Generate” button. A .zip will download. Unzip it. Inside you’ll find a simple, Maven-based project including a pom.xml build file (NOTE: You can use Gradle. The examples in this tutorial will be Maven-based.)

Import the project to your favorite IDE.

Configuring RabbitMQ connection

To integrate RabbitMQ in your Spring-powered web applications, first you need to do is configure RabbitMQ connection settings.

Spring for RabbitMQ provides a convenient class called RabbitTemplate to send and receive messages

By default RabbitTemplate class uses following configuration to connect to RabbitMQ instance.

host: localhost

port: 5672 (non -SSL) 5671 (SSL)

username: guest

password: guest

Using application.properties

You can also configure connection to RabbitMQ instance using application.properties.

In real world application you need configure using application properties only.

spring.rabbitmq.host=localhost spring.rabbitmq.port=5672 (non-SSL) or 5671 (SSL) spring.rabbitmq.username=guest spring.rabbitmq.password=guest
Code language: plaintext (plaintext)

Let’s see how to setup the Topic exchange ,queues and bindings programmatically in Spring Boot application.

We create a configuration class to create topic exchange ,queues and bindings

package dev.fullstackcode.sb.rabbitmq.producer.config; import org.springframework.amqp.core.Binding; import org.springframework.amqp.core.BindingBuilder; import org.springframework.amqp.core.Queue; import org.springframework.amqp.core.TopicExchange; import org.springframework.amqp.rabbit.connection.ConnectionFactory; import org.springframework.amqp.rabbit.core.RabbitTemplate; import org.springframework.amqp.support.converter.Jackson2JsonMessageConverter; import org.springframework.amqp.support.converter.MessageConverter; import org.springframework.boot.ApplicationRunner; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class RabbitMQConfiguration { @Bean Queue queueA() { return new Queue("queue.A", false); } @Bean Queue queueB() { return new Queue("queue.B", false); } @Bean Queue queueC() { return new Queue("queue.C", false); } @Bean TopicExchange exchange() { return new TopicExchange("exchange.topic"); } @Bean Binding bindingA(Queue queueA, TopicExchange exchange) { return BindingBuilder.bind(queueA).to(exchange).with("report.monthly.#"); } @Bean Binding bindingB(Queue queueB, TopicExchange exchange) { return BindingBuilder.bind(queueB).to(exchange).with("report.*.weekly"); } @Bean Binding bindingC(Queue queueC, TopicExchange exchange) { return BindingBuilder.bind(queueC).to(exchange).with("report.#"); } @Bean ApplicationRunner runner(ConnectionFactory cf) { return args -> cf.createConnection().close(); } @Bean MessageConverter messageConverter() { return new Jackson2JsonMessageConverter(); } @Bean RabbitTemplate rabbitTemplate(ConnectionFactory connectionFactory) { RabbitTemplate rabbitTemplate = new RabbitTemplate(connectionFactory); rabbitTemplate.setMessageConverter(messageConverter()); return rabbitTemplate; } }
Code language: Java (java)

Queue – beans are used to create queue

TopicExchange – beans are used to create Topic exchange

Binding – beans are used to create bindings between exchange and Queue.

MessageConverter – is used to convert object to Json format

RabbitTemplate – is used to configure the RabbitTemplate.

Creating Exchange and Queues on Startup

Spring Boot application connects to RabbitMQ server instance and creates Exchange and Queues when first message is published . If you want your application to create Exchange and Queues on application startup , you should use following method.

@Bean ApplicationRunner runner(ConnectionFactory cf) { return args -> cf.createConnection().close(); }
Code language: Java (java)

Publishing Messages

Once RabbitTemplate is configured , it is very easy to publish messages. We can use overloaded send/convertAndSend method to publish messages.

Let’s develop a controller class which publishes messages.

package dev.fullstackcode.sb.rabbitmq.producer.controller; import dev.fullstackcode.sb.rabbitmq.producer.model.Event; import org.springframework.amqp.core.TopicExchange; import org.springframework.amqp.rabbit.core.RabbitTemplate; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.http.HttpStatus; import org.springframework.web.bind.annotation.PostMapping; import org.springframework.web.bind.annotation.RequestBody; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RestController; import org.springframework.web.server.ResponseStatusException; @RestController @RequestMapping(value ="rabbitmq/event") public class RabbitMQProducerController { @Autowired private RabbitTemplate rabbitTemplate; @Autowired private TopicExchange topicExchange; @PostMapping public String send(@RequestBody Event event){ if( event.getName().equalsIgnoreCase("Event A")) { rabbitTemplate.convertAndSend(topicExchange.getName(), "report.monthly", event); } else if (event.getName().equalsIgnoreCase("Event B")) { rabbitTemplate.convertAndSend(topicExchange.getName(), "report.retail.weekly", event); } else if (event.getName().equalsIgnoreCase("Event X")) { rabbitTemplate.convertAndSend(topicExchange.getName(), "report.business.weekly", event); }else { throw new ResponseStatusException(HttpStatus.BAD_REQUEST,"unknown event"); } return "message sent successfully"; } }
Code language: Java (java)

Starting the RabbitMQ

Let’s use following docker compose file for starting RabbitMQ server in local development for our testing.

version: '3' services: rabbitmq: container_name: rabbitmq hostname: my-rabbitmq image: rabbitmq:3.10.6-management-alpine ports: - '5672:5672' - '15672:15672'
Code language: Java (java)
docker-compose up
Code language: plaintext (plaintext)

Starting Spring Boot RabbitMQ producer Application

Let’s start the springboot-raabitmq-producer application and publish some messages.

As we are connecting to RabbitMQ server on startup, it should create Direct Exchange and Queues and bindings in RabbitMQ instance.

We can check this by going to management console of RabbitMQ. It is available at

http://localhost:15672

username/password -> guest/guest

Below images confirm that exchange, queue and bindings created successfully on startup.

Publishing Messages

Let’s publish messages by sending request to controller class using rest client

Let’s look at the management console.

queue.A -> 1 message (Event A)

queue.B ->1 message (Event B)

queue.C -> 2 messages (Event A,Event B) as it matches routing key of both Event A and Event B.

Setup Consumer Project

To setup consumer project, you can follow the same procedure explained in producer setup section

Consuming Messages

Now let’s develop a consumer application which consumes messages from RabbitMQ server.

First define MessageConverter to Convert Json String back to Object as we are sending Object in json format from producer.

package com.fullstackcode.sb.rabbitmq.consumer.config; import org.springframework.amqp.support.converter.Jackson2JsonMessageConverter; import org.springframework.amqp.support.converter.MessageConverter; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class RabbitMQConfiguration { @Bean MessageConverter messageConverter() { return new Jackson2JsonMessageConverter(); } }
Code language: Java (java)

@RabbitListener annotation is used to receive messages from RabbitMQ queues.

Spring Boot will take care of converting message to corresponding Object

package com.fullstackcode.sb.rabbitmq.consumer.listener; import com.fullstackcode.sb.rabbitmq.consumer.model.Event; import lombok.extern.slf4j.Slf4j; import org.springframework.amqp.rabbit.annotation.RabbitListener; import org.springframework.amqp.rabbit.core.RabbitTemplate; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Component; @Component @Slf4j public class RabbitMQConsumer { @RabbitListener(queues = "queue.A") private void receiveQueueA(Event event) { log.info("Event received from queue A -> {}",event); } @RabbitListener(queues = "queue.B") private void receiveQueueB(Event event) { log.info("Event received from queue B -> {}",event); } @RabbitListener(queues = "queue.C") private void receiveQueueC(Event event) { log.info("Event received from queue C -> {}",event); } }
Code language: Java (java)

If you want to configure server properties uisng application.properties

spring.rabbitmq.host=localhost spring.rabbitmq.port=5672 (non-SSL) or 5671 (SSL) spring.rabbitmq.username=guest spring.rabbitmq.password=guest server.port=8081
Code language: plaintext (plaintext)

Once we start the consumer application, we can see following output on the console.

INFO : Event received from queue A -> Event(id=1, name=Event A) INFO : Event received from queue B -> Event(id=2, name=Event B) INFO : Event received from queue C -> Event(id=2, name=Event B) INFO : Event received from queue C -> Event(id=1, name=Event A)
Code language: Java (java)

Connecting to Remote Host

The above consumer example connects to RabbitMQ instance running in local

If you want to connect to instance running on server, you need specify the server address in application.properties

You can configureaddress like below

For SSL connection

spring.rabbitmq.addresses=amqps://<username>:<password>@<host>/<virtual-host>
Code language: Java (java)

For non-SSL connection

spring.rabbitmq.addresses=amqp://<username>:<password>@<host>/<virtual-host>
Code language: Java (java)

If you prefer individual properties, you can also configure like below

spring.rabbitmq.host=<host> spring.rabbitmq.virtual-host=<virtaul-host> spring.rabbitmq.port=5671 (SSL) or 5672 ( non - SSL) spring.rabbitmq.username=<username> spring.rabbitmq.password=<password>
Code language: Java (java)

Note

RabbitMQ in general listens on port 5672. If RabbitMQ instance is running on SSL, it will listen on port 5671

You can download source code from GitHub

producer – https://github.com/sureshgadupu/sb-rabbitmq-topicexchange

consumer – https://github.com/sureshgadupu/sb-rabbitmq-topicexchange-consumer

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