Separate DTO and Entity in Spring Boot: Best Practices and Benefits

Imagine you just joined a new Spring Boot project that’s been running smoothly for months, but you’ve noticed something strange. Entities are directly used in the controllers, returning database models as API responses. Initially, it might seem simpler—as you save writing extra classes—but is this the best approach? Recently, your senior developer suggested separating DTOs and Entities instead. So, what exactly are these DTOs and why should you consider switching to this architecture?

Understanding DTO and Entity

Before we go further, let’s define some fundamental concepts clearly. First up—DTO (Data Transfer Object). Simply put, a DTO is an object specifically used for transferring data between processes, such as between a client and server, without business logic. Think of a DTO as a courier delivering an order: its job isn’t thinking about the contents, simply delivering it safely from sender to receiver.

Next, we have Entities. Entities, in Spring Boot projects using Java Persistence API (JPA), represent database tables. They typically correlate directly to tables and carry annotations like @Entity. An entity carries both data structure and persistence logic, making it heavier compared to DTO.

Keeping these two separate may seem redundant initially, but there’s a significant advantage. In fact, separating DTO and Entity classes enhances the application’s clarity and provides flexibility if the database structure later changes.

Best Practices in Spring Boot: Why They Matter

Spring Boot, a popular framework for developing Spring-based applications, encourages good design patterns and architecture. By adhering to established best practices, you ensure your code is maintainable, scalable, and robust. One major best practice in Spring Boot development is isolating entities from the outside world (e.g., REST controllers) by incorporating separate DTOs.

Why is this practice often recommended and widely adopted in established Spring Boot applications? Let’s explore some of its key advantages.

The Benefits of Separating DTO and Entity

Improved Code Maintainability
Consider this scenario—you have a User entity linked directly to your API response in the controller. Later on, you want to change the database columns or add some internal fields not meant for the API user. If your entities are exposed directly to the client application, every database change could potentially cascade into a breaking API change. By separating DTOs, database modifications won’t impact your API contract directly.

Easier Data Validation
Another benefit of employing DTOs lies in simplified data validation. You can easily apply specific validation annotations like @NotNull, @Size, @Email directly on DTO fields without muddling your entity configuration. Keeping validation logic separate from persistence logic ensures cleaner code that’s easier to maintain over time.

Enhanced Flexibility in API Design
One client might require only certain fields, while another client requests entirely different sets of data. Separate DTOs provide fine-grained control. You can quickly adapt and provide exactly what each client needs without overloading APIs. Plus, versioning and enhancing APIs becomes simpler and more intuitive.

Comparing Current Approach with Senior Developer’s Suggestion

In your current scenario, your project directly utilizes entities to map API responses. Let’s break this down on a practical level to get clearer insight:

Your current approach may look somewhat like this:

@RestController
@RequestMapping("/users")
public class UserController {

  @Autowired
  private UserRepository userRepository;

  @GetMapping("/{id}")
  public User getUser(@PathVariable Long id) {
    return userRepository.findById(id)
        .orElseThrow(() -> new ResourceNotFoundException());
  }
}

While this directly returns a JPA entity, let’s explore your senior developer’s new suggested technique using a separate DTO class:

@RestController
@RequestMapping("/users")
public class UserController {

  @Autowired
  private UserRepository userRepository;

  @GetMapping("/{id}")
  public UserDTO getUser(@PathVariable Long id) {
    User user = userRepository.findById(id)
        .orElseThrow(() -> new ResourceNotFoundException());

    return new UserDTO(user.getId(), user.getName(), user.getEmail());
  }
}

Pros & Cons of Current vs. Separate DTO Approach:

Exploring the Use of the StudentResource Entity Class

Let’s say your project includes a class called StudentResource that currently combines the entity’s role and the API-facing resource. This represents the scenario you might encounter when entities are directly coupled to REST responses. While initially simple, it often creates tight coupling that can be problematic down the road.

By clearly defining a DTO—such as StudentResourceDTO—you’ll avoid mixing database annotations, entity logic, or additional internal fields with your API contracts. Moreover, this keeps things explicit and organized, aligning with maintainability and good software development practices.

Analyzing Redundancy Concerns

It’s common to question if having two seemingly similar classes (a DTO and an Entity) creates redundancy. While initially similar in structure, these two serve entirely different purposes. Keeping DTOs and Entities separate means your APIs aren’t tightly bound to your database implementation. Thus, minor database changes won’t break client applications unexpectedly.

Moreover, you can design DTOs to suit client-specific needs without cluttering your database entities. As a result, redundancy here is more of front-loaded convenience, leading to long-term stability, clarity, and ease of future development.

Looking at Design Patterns and Industry Standards

DTO and Entity separation isn’t just an opinion—it’s a widely accepted software design pattern adopted industry-wide. Patterns like DTOs, repositories, services, and MVC (model-view-controller) architecture stem from proven best practices promoted by experts and documented widely, such as in Martin Fowler’s popular book on Data Transfer Objects (DTO).

Spring Boot itself promotes the notion of layering your architecture. By clearly separating concerns through different classes and clearly-defined DTOs, your application improves greatly in readability, maintainability, and extendability.

Wrapping It Up: Should You Implement Separate DTO Classes?

Clearly, separating DTOs and Entities in your Spring Boot projects makes good sense. Although it initially introduces additional layers, the benefits far outweigh this simple effort. Increased maintainability, better flexibility, cleaner validation rules, and alignment with industry standards all point toward naturally adopting this best practice.

If you haven’t done it yet, it’s worth revisiting your project’s architecture. Start small; pick any new feature or module and try implementing separate DTOs. The long-term benefits you’ll gain in software quality are worth the minor upfront implementation time.

So, are you ready to enhance your Spring Boot applications using DTO and Entity separation? Why not start now—experiment with a small implementation and witness these advantages firsthand!