Quarkus Patterns

# Quarkus Development Patterns

Quarkus 3.x architecture and API patterns for cloud-native, event-driven services with Apache Camel.

## When to Activate

- Building REST APIs with JAX-RS or RESTEasy Reactive
- Structuring resource → service → repository layers
- Implementing event-driven patterns with Apache Camel and RabbitMQ
- Configuring Hibernate Panache, caching, or reactive streams
- Adding validation, exception mapping, or pagination
- Setting up profiles for dev/staging/production environments (YAML config)
- Custom logging with LogContext and Logback/Logstash encoder
- Working with CompletableFuture for async operations
- Implementing conditional flow processing
- Working with GraalVM native compilation

## Service Layer with Multiple Dependencies

```java
@Slf4j
@ApplicationScoped
@RequiredArgsConstructor
public class OrderProcessingService {

    private final OrderValidator orderValidator;
    private final EventService eventService;
    private final OrderRepository orderRepository;
    private final FulfillmentPublisher fulfillmentPublisher;
    private final AuditPublisher auditPublisher;

    @Transactional
    public OrderReceipt process(CreateOrderCommand command) {
        ValidationResult validation = orderValidator.validate(command);
        if (!validation.valid()) {
            eventService.createErrorEvent(command, "ORDER_REJECTED", validation.message());
            throw new WebApplicationException(validation.message(), Response.Status.BAD_REQUEST);
        }

        Order order = Order.from(command);
        orderRepository.persist(order);

        OrderReceipt receipt = OrderReceipt.from(order);
        fulfillmentPublisher.publishAsync(receipt);
        auditPublisher.publish("ORDER_ACCEPTED", receipt);
        eventService.createSuccessEvent(receipt, "ORDER_ACCEPTED");

        log.info("Processed order {}", order.id);
        return receipt;
    }
}
```

**Key Patterns:**
- `@RequiredArgsConstructor` for constructor injection via Lombok
- `@Slf4j` for Logback logging
- `@Transactional` on service methods that write through Panache or repositories
- Validate input before persistence or message publication
- Event tracking for success/error scenarios
- Async Camel message publishing

## Custom Logging Context Pattern (Logback)

```java
@ApplicationScoped
public class ProcessingService {

    public void processDocument(Document doc) {
        LogContext logContext = CustomLog.getCurrentContext();
        try (SafeAutoCloseable ignored = CustomLog.startScope(logContext)) {
            // Add context to all log statements
            logContext.put("documentId", doc.getId().toString());
            logContext.put("documentType", doc.getType());
            logContext.put("userId", SecurityContext.getUserId());

            log.info("Starting document processing");

            // All logs within this scope inherit the context
            processInternal(doc);

            log.info("Document processing completed");
        } catch (Exception e) {
            log.error("Document processing failed", e);
            throw e;
        }
    }
}
```

**Logback Configuration (logback.xml):**

```xml
<configuration>
    <appender name="CONSOLE" class="ch.qos.logback.core.ConsoleAppender">
        <encoder class="net.logstash.logback.encoder.LogstashEncoder">
            <includeContext>true</includeContext>
            <includeMdc>true</includeMdc>
        </encoder>
    </appender>

    <logger name="com.example" level="INFO"/>
    <root level="WARN">
        <appender-ref ref="CONSOLE"/>
    </root>
</configuration>
```

## Event Service Pattern

```java
@Slf4j
@ApplicationScoped
@RequiredArgsConstructor
public class EventService {
    priv