RabbitMQ and Micronaut - Event driven applications
Use RabbitMQ to communicate your Micronaut apps.
Authors: Iván López
Micronaut Version: 2.5.0
1. Getting Started
In this guide we are going to create a Micronaut app written in Java.
In this guide, we are going to create two microservices that will use RabbitMQ to communicate each other in an asynchronous and decoupled way.
RabbitMQ is an open-source message-broker software that originally implemented the Advanced Message Queuing Protocol (AMQP) and has since been extended with a plug-in architecture to support Streaming Text Oriented Messaging Protocol (STOMP), Message Queuing Telemetry Transport (MQTT), and other protocols.
2. What you will need
To complete this guide, you will need the following:
-
Some time on your hands
-
A decent text editor or IDE
-
JDK 1.8 or greater installed with
JAVA_HOME
configured appropriately
3. Solution
We recommend that you follow the instructions in the next sections and create the app step by step. However, you can go right to the completed example.
-
Download and unzip the source
4. Writing the app
Let’s describe the microservices you are going to build through the tutorial.
-
books
- It returns a list of books. It uses a domain consisting of a book name and isbn. It also publishes a message in RabbitMQ every time a book is accessed. -
analytics
- It connects to RabbitMQ to update the analytics for every book (a counter). It also exposes an endpoint to get the analytics.
If you are using Java or Kotlin and IntelliJ IDEA, make sure you have enabled annotation processing.
4.1. Books microservice
Create the books
microservice:
mn create-app example.micronaut.books
The previous command creates a folder named books
and a Micronaut app inside it with default package:
example.micronaut
.
Create a BookController
class to handle incoming HTTP requests into the books
microservice:
package example.micronaut;
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
import java.util.List;
import java.util.Optional;
@Controller("/books") (1)
public class BookController {
private final BookService bookService; (2)
public BookController(BookService bookService) {
this.bookService = bookService;
}
@Get (3)
public List<Book> listAll() {
return bookService.listAll();
}
@Get("/{isbn}") (4)
Optional<Book> findBook(String isbn) {
return bookService.findByIsbn(isbn);
}
}
1 | The class is defined as a controller with the @Controller
annotation mapped to the path /books |
2 | Inject BookService using constructor injection. |
3 | The @Get annotation is used to map the listAll method to an HTTP GET request on /books . |
4 | The @Get annotation is used to map the findBook method to an HTTP GET request on /books/{isbn} . |
The previous controller responds a List<Book>
. Create the Book
POJO:
package example.micronaut;
import io.micronaut.core.annotation.Introspected;
import java.util.Objects;
@Introspected
public class Book {
private String isbn;
private String name;
public Book() {
}
public Book(String isbn, String name) {
this.isbn = isbn;
this.name = name;
}
public String getIsbn() {
return isbn;
}
public void setIsbn(String isbn) {
this.isbn = isbn;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Book{" +
"isbn='" + isbn + '\'' +
", name='" + name + '\'' +
'}';
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Book book = (Book) o;
return Objects.equals(isbn, book.isbn) &&
Objects.equals(name, book.name);
}
@Override
public int hashCode() {
return Objects.hash(isbn, name);
}
}
To keep this guide simple there is no database persistence, and the list of books is kept in memory in BookService
:
package example.micronaut;
import javax.annotation.PostConstruct;
import javax.inject.Singleton;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
@Singleton
public class BookService {
private static final List<Book> bookStore = new ArrayList<>();
@PostConstruct
void init() {
bookStore.add(new Book("1491950358", "Building Microservices"));
bookStore.add(new Book("1680502395", "Release It!"));
bookStore.add(new Book("0321601912", "Continuous Delivery"));
}
public List<Book> listAll() {
return bookStore;
}
public Optional<Book> findByIsbn(String isbn) {
return bookStore.stream()
.filter(b -> b.getIsbn().equals(isbn))
.findFirst();
}
}
4.2. Analytics microservice
Create the analytics
microservice:
mn create-app example.micronaut.analytics
To keep this guide simple there is no database persistence, and the books analytics is kept in memory in AnalyticsService
:
package example.micronaut;
import javax.inject.Singleton;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.stream.Collectors;
@Singleton
public class AnalyticsService {
private final Map<Book, Long> bookAnalytics = new ConcurrentHashMap<>(); (1)
public void updateBookAnalytics(Book book) { (2)
bookAnalytics.compute(book, (b, v) -> {
if (v == null) {
return 1L;
} else {
return v + 1;
}
});
}
public List<BookAnalytics> listAnalytics() { (3)
return bookAnalytics
.entrySet()
.stream()
.map(e -> new BookAnalytics(e.getKey().getIsbn(), e.getValue()))
.collect(Collectors.toList());
}
}
1 | Keep the books analytics in memory. |
2 | Initialize and update the analytics for the book passed as parameter. |
3 | Return all the analytics. |
The previous service responds a List<BookAnalytics>
. Create the BookAnalytics
POJO:
package example.micronaut;
import io.micronaut.core.annotation.Introspected;
@Introspected
public class BookAnalytics {
private String bookIsbn;
private Long count;
public BookAnalytics() {
}
public BookAnalytics(String bookIsbn, Long count) {
this.bookIsbn = bookIsbn;
this.count = count;
}
public String getBookIsbn() {
return bookIsbn;
}
public void setBookIsbn(String bookIsbn) {
this.bookIsbn = bookIsbn;
}
public Long getCount() {
return count;
}
public void setCount(Long count) {
this.count = count;
}
}
Write a test:
package example.micronaut;
import static org.junit.jupiter.api.Assertions.assertEquals;
import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
import org.junit.jupiter.api.Test;
import javax.inject.Inject;
import java.util.List;
@MicronautTest (1)
public class AnalyticsServiceTest {
@Inject (2)
AnalyticsService analyticsService;
@Test
void testUpdateBookAnalyticsAndGetAnalytics() {
Book b1 = new Book("1491950358", "Building Microservices");
Book b2 = new Book("1680502395", "Release It!");
analyticsService.updateBookAnalytics(b1);
analyticsService.updateBookAnalytics(b1);
analyticsService.updateBookAnalytics(b1);
analyticsService.updateBookAnalytics(b2);
List<BookAnalytics> analytics = analyticsService.listAnalytics();
assertEquals(2, analytics.size());
assertEquals(3, findBookAnalytics(b1, analytics).getCount().intValue());
assertEquals(1, findBookAnalytics(b2, analytics).getCount().intValue());
}
private BookAnalytics findBookAnalytics(Book b, List<BookAnalytics> analytics) {
return analytics
.stream()
.filter(bookAnalytics -> bookAnalytics.getBookIsbn().equals(b.getIsbn()))
.findFirst()
.orElseThrow(() -> new RuntimeException("Book not found"));
}
}
1 | Starting with Micronaut 1.1.0 micronaut-test-junit5 is added automatically to build.gradle (or pom.xml ) when
creating an application with the CLI. For more information take a look at the documentation. |
2 | Just inject the collaborator and @MicronautTest will take care of everything. |
Create a Controller to expose the analytics:
package example.micronaut;
import io.micronaut.http.annotation.Controller;
import io.micronaut.http.annotation.Get;
import java.util.List;
@Controller("/analytics")
public class AnalyticsController {
private final AnalyticsService analyticsService;
public AnalyticsController(AnalyticsService analyticsService) {
this.analyticsService = analyticsService;
}
@Get("/") (1)
public List<BookAnalytics> listAnalytics() {
return analyticsService.listAnalytics();
}
}
1 | Just expose the analytics. |
The application doesn’t expose the method |
To run the tests:
analytics $ ./mvnw test
Finally edit application.yml
to run the application on a different port that books
microservice.
micronaut:
server:
port: 8081 (1)
1 | Start the Micronaut microservice on port 8081. |
5. Running the app
Run books
microservice:
books $ ./mvnw mn:run
16:35:55.614 [main] INFO io.micronaut.runtime.Micronaut - Startup completed in 576ms. Server Running: http://localhost:8080
Run analytics
microservice:
analytics $ ./mvnw mn:run
16:35:55.614 [main] INFO io.micronaut.runtime.Micronaut - Startup completed in 623ms. Server Running: http://localhost:8081
You can run a curl
command to test the application:
$ curl http://localhost:8080/books
[{"isbn":"1491950358","name":"Building Microservices"},{"isbn":"1680502395","name":"Release It!"},{"isbn":"0321601912","name":"Continuous Delivery"}]
$ curl http://localhost:8080/books/1491950358
{"isbn":"1491950358","name":"Building Microservices"}
$ curl http://localhost:8081/analytics
[]
Please note that getting the analytics returns an empty list because the applications are not communicating to each other (yet).
6. RabbitMQ and Micronaut
6.1. Install RabbitMQ via Docker
The fastest way to start using RabbitMQ is via Docker:
docker run --rm -it \
-p 5672:5672 \
-p 15672:15672 \
rabbitmq:3.8.12-management
Alternatively you can install and run a local RabbitMQ instance.
6.2. Books microservice
Add rabbitmq
dependency.
<dependency>
<groupId>io.micronaut.rabbitmq</groupId>
<artifactId>micronaut-rabbitmq</artifactId>
<scope>compile</scope>
</dependency>
By default Micronaut will connect to a RabbitMQ instance running on localhost
so it is not necessary to add anything
to application.yml
. In case you want to change the configuration, add the following:
rabbitmq:
uri: amqp://localhost:5672
6.2.1. Create RabbitMQ exchange, queue and binding
Before being able to send and receive messages using RabbitMQ it is necessary to define the exchange, queue and binding.
One option is create them directly in the RabbitMQ Admin UI available on http://localhost:15672
.Use guest
for both
username and password.
Another option is create them programatically with Micronaut.Create the class ChannelPoolListener
:
package example.micronaut;
import com.rabbitmq.client.BuiltinExchangeType;
import com.rabbitmq.client.Channel;
import io.micronaut.rabbitmq.connect.ChannelInitializer;
import javax.inject.Singleton;
import java.io.IOException;
@Singleton
public class ChannelPoolListener extends ChannelInitializer {
@Override
public void initialize(Channel channel) throws IOException {
channel.exchangeDeclare("micronaut", BuiltinExchangeType.DIRECT, true); (1)
channel.queueDeclare("analytics", true, false, false, null); (2)
channel.queueBind("analytics", "micronaut", "analytics"); (3)
}
}
1 | Define an exchange named micronaut .From the producer point of view everything is sent to the exchange with the
appropriate routing key |
2 | Define a queue named analytics .The consumer will listen for messages in that queue. |
3 | Define a binding between the exchange and the queue using the routing key analytics . |
6.2.2. Create RabbitMQ client (producer)
Let’s create an interface to send messages to RabbitMQ. Micronaut will implement the interface at compilation time:
package example.micronaut;
import io.micronaut.rabbitmq.annotation.Binding;
import io.micronaut.rabbitmq.annotation.RabbitClient;
@RabbitClient("micronaut") (1)
public interface AnalyticsClient {
@Binding("analytics") (2)
void updateAnalytics(Book book); (3)
}
1 | Set the exchange used to send the messages. |
2 | Set the routing key. |
3 | Send the Book POJO. Micronaut will automatically convert it to JSON before sending it. |
6.2.3. Send Analytics information automatically
Sending a message to RabbitMQ is as simple as injecting AnalyticsClient
and calling updateAnalytics
method. The goal
is to do it automatically every time a book is returned, i.e., every time there is a call to http://localhost:8080/books/{isbn}
.
To achieve this we are going to create an Http Server Filter.
Create the file AnalyticsFilter
:
package example.micronaut;
import io.micronaut.http.HttpRequest;
import io.micronaut.http.MutableHttpResponse;
import io.micronaut.http.annotation.Filter;
import io.micronaut.http.filter.HttpServerFilter;
import io.micronaut.http.filter.ServerFilterChain;
import io.reactivex.Flowable;
import org.reactivestreams.Publisher;
import java.util.Optional;
@Filter("/books/?*") (1)
public class AnalyticsFilter implements HttpServerFilter { (2)
private final AnalyticsClient analyticsClient; (3)
public AnalyticsFilter(AnalyticsClient analyticsClient) { (3)
this.analyticsClient = analyticsClient;
}
@Override
public Publisher<MutableHttpResponse<?>> doFilter(HttpRequest<?> request, ServerFilterChain chain) { (4)
return Flowable
.fromPublisher(chain.proceed(request)) (5)
.flatMap(response ->
Flowable.fromCallable(() -> {
Optional<Book> book = response.getBody(Book.class); (6)
book.ifPresent(analyticsClient::updateAnalytics); (7)
return response;
})
);
}
}
1 | Annotate the class with @Filter and define the ANT Matcher pattern to intercept all the calls to the desire URI. |
2 | The class needs to implement HttpServerFilter . |
3 | Constructor injection for RabbitMQ AnalyticsClient . |
4 | Override doFilter method. |
5 | Execute the request. This will call the controller action. |
6 | Get the response from the controller and return the body as a Book . |
7 | If the book is found, use RabbitMQ client to send a message. |
6.3. Analytics microservice
Add rabbitmq
dependency.
<dependency>
<groupId>io.micronaut.rabbitmq</groupId>
<artifactId>micronaut-rabbitmq</artifactId>
<scope>compile</scope>
</dependency>
6.3.1. Create RabbitMQ exchange, queue and binding
As we already did in Books Microservice, let’s create the class ChannelPoolListener
to define the exchange, queue
and binding:
package example.micronaut;
import com.rabbitmq.client.BuiltinExchangeType;
import com.rabbitmq.client.Channel;
import io.micronaut.rabbitmq.connect.ChannelInitializer;
import javax.inject.Singleton;
import java.io.IOException;
@Singleton
public class ChannelPoolListener extends ChannelInitializer {
@Override
public void initialize(Channel channel) throws IOException {
channel.exchangeDeclare("micronaut", BuiltinExchangeType.DIRECT, true);
channel.queueDeclare("analytics", true, false, false, null);
channel.queueBind("analytics", "micronaut", "analytics");
}
}
Instead of copy-paste the class in every project it would be better to create a new Gradle (or Maven) module and share it among all the microservices. |
6.3.2. Create RabbitMQ consumer
Create a new class to act as a consumer of the messages sent to RabbitMQ by the Books Microservice. Micronaut will
implement the consumer at compile time. Create AnalyticsListener
:
package example.micronaut;
import io.micronaut.rabbitmq.annotation.Queue;
import io.micronaut.rabbitmq.annotation.RabbitListener;
import io.micronaut.context.annotation.Requires;
import io.micronaut.context.env.Environment;
@Requires(notEnv = Environment.TEST) (1)
@RabbitListener (2)
public class AnalyticsListener {
private final AnalyticsService analyticsService; (3)
public AnalyticsListener(AnalyticsService analyticsService) { (3)
this.analyticsService = analyticsService;
}
@Queue("analytics") (4)
public void updateAnalytics(Book book) {
analyticsService.updateBookAnalytics(book); (5)
}
}
1 | Do not load this bean for the test environment. This enable us to run the tests without having a RabbitMQ instance running. |
2 | Annotate the class with @RabbitListener to indicate that this bean will consume messages from RabbitMQ. |
3 | Constructor injection for AnalyticsService . |
4 | Annotate the method with @Queue . This listener will listen to messages in analytics queue. |
5 | Call the previously created method to update the analytics for the book. |
6.4. Running the app
Run books
microservice:
books $ ./mvnw mn:run
16:35:55.614 [main] INFO io.micronaut.runtime.Micronaut - Startup completed in 576ms. Server Running: http://localhost:8080
Execute a curl
request to get one book:
$ curl http://localhost:8080/books/1491950358
{"isbn":"1491950358","name":"Building Microservices"}
Open RabbitMQ Admin UI on http://localhost:15672
and use guest
for both username and password. Select queues
and
analytics
queue. You can see that there is a message in the queue.
Expand the "Get messages" option and get one message. You can see all the information: exchange
, routing key, and the
`payload
serialized to json:
Run analytics
microservice:
analytics $ ./mvnw mn:run
16:35:55.614 [main] INFO io.micronaut.runtime.Micronaut - Startup completed in 623ms. Server Running: http://localhost:8081
The application will consume and process the message automatically after the startup. Go to RabbitMQ Admin UI and check that the message has been consumed:
Now, run a curl
to get the analytics:
$ curl http://localhost:8081/analytics
[{"bookIsbn":"1491950358","count":1}]
7. Generate a Micronaut app’s Native Image with GraalVM
We are going to use GraalVM, the polyglot embeddable virtual machine, to generate a Native image of our Micronaut application.
Native images compiled with GraalVM ahead-of-time improve the startup time and reduce the memory footprint of JVM-based applications.
Use of GraalVM’s native-image tool is only supported in Java or Kotlin projects. Groovy relies heavily on
reflection which is only partially supported by GraalVM.
|
7.1. Native Image generation
The easiest way to install GraalVM is to use SDKMan.io.
# For Java 8
$ sdk install java 21.1.0.r8-grl
# For Java 11
$ sdk install java 21.1.0.r11-grl
You need to install the native-image
component which is not installed by default.
$ gu install native-image
To generate a native image using Maven run:
$ ./mvnw package -Dpackaging=native-image
The native image will be created in target/application
and can be run with ./target/application
.
Start the native images for the two microservices and run the same curl
request as before to check that everything works with GraalVM.
8. Next steps
Read more about RabbitMQ support inside Micronaut.