If you are a developer and have not faced this issue yet, it is still worth reading, as at some point in your career, you will likely need to create a Spring Boot REST endpoint that performs a database query with results that do not fit into memory.

In this article, let’s delve into an example of a REST endpoint that cannot be implemented in the traditional way due to memory consumption.

Scenario

In this exercise, let’s use a simple scenario involving Customer, Order, OrderItem, and Product:

Our goal is to create an endpoint that will generate a report. This endpoint will query and return:

• One million Orders.
• More than 5 million OrderItems.

Traditional Implementation

Let’s define a DTO with some fields:

@Data
public class ReportDto {
  private final Long orderId;
  private final LocalDate date;
  private final String customerName;
  . . .
  private final List<Item> items;

  @Data
  public static class Item {…