RabbitMQ Event-Driven Microservices (Java, Non-Spring)

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A hands-on project that demonstrates an event-driven microservices approach using RabbitMQ and pure Java (no Spring).

Instead of REST calls, services communicate asynchronously through RabbitMQ exchanges + routing keys, highlighting the fundamentals of AMQP messaging, loose coupling, and message filtering.

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What’s inside

Microservices (simulated)

• MSReserva — reservation menu (publishes reservation events + receives notifications)
• MSPagamento — consumes reservations, simulates payment decision, digitally signs the result
• MSBilhete — verifies payment signature and issues tickets
• MSMarketing — publishes promotions by destination
• AssinantePromocoes — dynamic subscriber (bind/unbind routing keys at runtime)

Note: all services are in a single Maven module for simplicity (multiple main classes). The runtime behavior simulates microservices.

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Architecture overview

Reservation → Payment → Ticket flow (Exchange: EXG)

• MSReserva publishes a reservation event to EXG with routing key vermelho
• MSPagamento consumes vermelho, randomly approves/rejects payment, signs the message, and publishes to:
  • verde (approved) or
  • azul (rejected)
• MSBilhete consumes verde/azul
  • when approved, verifies the signature and publishes a ticket notification to amarelo
• MSReserva consumes verde, azul, and amarelo and stores notifications in an in-memory queue

Promotions flow (Exchange: PromocoesExchange)

• MSMarketing publishes promotions using routing keys: rio, salvador, manaus
• AssinantePromocoes creates an exclusive auto-delete queue and binds keys based on the user menu

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Exchanges, queues and routing keys

EXG (direct)

Purpose	Queue	Routing key
Reservation created → MSPagamento	mspagamento_reserva_criada	vermelho
Payment approved → MSReserva	pagamento-aprovado	verde
Payment rejected → MSReserva	pagamento-recusado	azul
Ticket issued → MSReserva	bilhete-emitido	amarelo
Payment approved → MSBilhete	msbilhete_pagamento_aprovado	verde
Payment rejected → MSBilhete	msbilhete_pagamento_recusado	azul

PromocoesExchange (direct)

Purpose	Queue	Routing key
Promotions subscriber	auto-generated (exclusive)	rio, salvador, manaus

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Message format (digital signature)

Payment events are published as:

<text>|<base64_signature>

Example:

Pagamento da reserva RESERVA-0001 aprovado|MEU...BASE64...==

• Signing algorithm: SHA256withDSA
• MSPagamento signs (private key)
• MSReserva and MSBilhete verify (public key)

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Prerequisites

• Java 8+ (project is configured for Java 8 in pom.xml)
• Maven 3+
• RabbitMQ running locally on localhost:5672

Optional (recommended):

• RabbitMQ Management UI (15672)

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Running RabbitMQ

Option A — Docker (recommended)

docker run --rm -it \
  -p 5672:5672 -p 15672:15672 \
  rabbitmq:3-management

Management UI: http://localhost:15672 (default: guest/guest)

Option B — Local install

Start RabbitMQ and keep the default ports.

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Keys setup (required for signature)

The key loader uses a fixed Windows path in cript/KeyReaderExample.java: C:\Users\Afonso\Desktop\keys

You have two options:

1. Create keys in that folder (Windows), or
2. Edit the constant DIRECTORY_PATH to point to your machine.

To generate keys, run:

• cript.KeyGeneratorExample

It will create:

• private.key
• public.key

Tip: don’t commit your private.key to Git.

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How to run (recommended order)

You can run each service from your IDE (multiple run configurations) or from the terminal.

Build once

mvn -q -DskipTests package

Start services (each in a separate terminal)

1. MSPagamento

mvn -q exec:java -Dexec.mainClass=com.exemplo.rabbitmq.MSPagamento

2. MSBilhete

mvn -q exec:java -Dexec.mainClass=com.exemplo.rabbitmq.MSBilhete

3. MSReserva

mvn -q exec:java -Dexec.mainClass=com.exemplo.rabbitmq.MSReserva

4. (Optional) AssinantePromocoes (subscribe to rio/salvador/manaus)

mvn -q exec:java -Dexec.mainClass=com.exemplo.rabbitmq.AssinantePromocoes

5. (Optional) MSMarketing (publishes promotions with delays)

mvn -q exec:java -Dexec.mainClass=com.exemplo.rabbitmq.MSMarketing

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Why “Non-Spring”?

This project intentionally avoids Spring to demonstrate:

• manual exchange/queue declarations
• routing key filtering
• raw RabbitMQ Java client usage
• the core mechanics behind Spring AMQP abstractions

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Possible improvements (roadmap ideas)

• Use JSON messages (schema/versioning)
• Add manual ack, retries and DLQ
• Add correlation IDs / tracing metadata
• Externalize configuration (host, exchange names, key paths)
• Split into multi-module (one module per microservice)
• Provide a Spring AMQP version for comparison

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License

Educational/demo project — feel free to use as a reference.