dev-aritra

  public void handle(Message<String> message)
      throws RetryableException, DroppableException, DlqableException {
    try {
      doStuff(message);
    } catch (IllegalArgumentException ex) {
      throw new DlqableException(ex);
    }
  }

dev-aritra

  public RetryTemplate eventConsumerRetryTemplate(int maxAttempts) {
    return RetryTemplate.builder()
        .retryOn(RetryableException.class)
        .maxAttempts(maxAttempts)
        .exponentialBackoff(100, 2, 300)
        .traversingCauses()
        .build();
  }

dev-aritra

public void consume(Message<String> message) {
    try {
      final EventHandler handler = subscriptionMap.get(event); // Selecting a appropriate handler based on the message
      processWithRetry(handler, message);
    } catch (RequeableException e) {
      failureHandler.reQueue(message, e);
    } catch (DroppableException e) {
      failureHandler.dropMessage(message, e);
    } catch (Exception e) {
      failureHandler.putOnDlq(message, e);

dev-aritra

    @Transactional
    public Optional<Order> placeOrder(Long productId, Long userId) {
        Optional<Product> product = productRepository.findByIdWithWriteLock(productId);
        product.orElseThrow(() -> new RuntimeException("Invalid product id"));

        if (product.get().getAvailableUnits() > 0) {
            productRepository.decrementAvailableUnitsCountBy1(productId);
            Order newOrder = new Order(userId, productId);
            orderRepository.save(newOrder);
            return Optional.of(newOrder);

dev-aritra

    @Query(value = "select * from products where id = ?1 for update", nativeQuery = true)
    Optional<Product> findByIdWithWriteLock(Long productId);

dev-aritra

    @Query("update products set available_units = available_units - 1 where id = ?1")
    @Modifying
    void decrementAvailableUnitsCountBy1(Long productId);

dev-aritra

    @Transactional
    public Optional<Order> placeOrder(Long productId, Long userId) {
        Optional<Product> product = productRepository.findById(productId);
        product.orElseThrow(() -> new RuntimeException("Invalid product id"));

        if (product.get().getAvailableUnits() > 0) {
            productRepository.decrementAvailableUnitsCountBy1(productId);
            Order newOrder = new Order(userId, productId);
            orderRepository.save(newOrder);
            return Optional.of(newOrder);

dev-aritra

    @Test
    void shouldCreateOrder() throws InterruptedException {
        Product iPhone12 = new Product("iPhone12", 1);
        productRepository.saveAndFlush(iPhone12); // Insert product with count 1 into DB

        ExecutorService threadPool = Executors.newFixedThreadPool(10); // Create a threadpool with 10 threads
        List<Callable<Optional<Order>>> orderRequests = getOrderRequests(iPhone12.getId(), 20); // Create 20 tasks for placing 20 orders
        List<Future<Optional<Order>>> results = threadPool.invokeAll(orderRequests); // Place those 20 orders simulteanously 

        long successCount = results.stream() // Calculate how many orders got placed successfully

dev-aritra

{
  "level" : "ERROR",
  "message" : "NullPointerException"
}

dev-aritra

@Data
@AllArgsConstructor
public class StorePresenter {
  private String id;
  private final String name;
  private final String zipCode;
  private final Double latitude;
  private final Double longitude;