Apache ActiveMQActiveMQ

Producer → Broker → Consumer
             │
     ┌───────┴───────┐
     Queue           Topic
  (1:1 전달)    (발행-구독)
     │               │
  Consumer       Subscriber(들)
  (하나만 수신)  (모두 수신)

메시지 영속성:
  - KahaDB (기본): 내장 저장소
  - JDBC: 외부 DB 저장
  - LevelDB: 고성능 KV 저장소

// Spring Boot + ActiveMQ
// build.gradle: implementation 'org.springframework.boot:spring-boot-starter-activemq'

@Configuration
public class ActiveMQConfig {
    @Bean
    public ConnectionFactory connectionFactory() {
        return new ActiveMQConnectionFactory("tcp://localhost:61616");
    }
    @Bean
    public JmsTemplate jmsTemplate(ConnectionFactory cf) {
        return new JmsTemplate(cf);
    }
}

// 메시지 전송
@Service
public class OrderProducer {
    @Autowired JmsTemplate jmsTemplate;

    public void send(Order order) {
        jmsTemplate.convertAndSend("order.queue", order);
    }
}

// 메시지 수신
@Component
public class OrderConsumer {
    @JmsListener(destination = "order.queue")
    public void receive(Order order) {
        System.out.println("처리: " + order.getId());
    }
}

<!-- activemq.xml 설정 -->
<policyEntry queue="order.queue">
  <deadLetterStrategy>
    <individualDeadLetterStrategy
      queuePrefix="DLQ."
      useQueueForQueueMessages="true"
      expiration="604800000" /> <!-- 7일 보존 -->
  </deadLetterStrategy>
  <redeliveryPolicy maximumRedeliveries="3" redeliveryDelay="5000" />
</policyEntry>