Why Use DTOs in Spring Boot?
1. Decoupling: DTOs help to decouple the presentation layer from the service layer. With DTOs, the presentation layer does not need to know about the internal structure of the domain objects used by the service layer. This allows for a cleaner separation of concerns & makes the application more maintainable.
2. Data Hiding: DTOs allow you to expose only the data needed by the client while hiding the internal details of the domain objects. This can help reduce the amount of data that needs to be transferred over the network and can also improve security by preventing sensitive data from being exposed.
3. Flexibility: DTOs provide a way to customize the data that is sent to the client without having to modify the domain objects. This can be useful when the client requires a different representation of the data than what is used by the service layer.
4. Performance: DTOs can improve performance by reducing the number of method calls required to retrieve data from a remote interface. By retrieving all the necessary data in a single call, DTOs can help reduce network overhead and improve the application's overall performance.
5. Versioning: DTOs can help to manage changes to the API contract over time. By creating a new version of the DTO, you can add or remove fields without breaking existing clients that are using the old version of the DTO.
Creating DTOs in a Spring Boot Application
To create a DTO in a Spring Boot application, you simply need to define a new class that contains the fields you want to transfer.
Let’s see an example of what a DTO might look like:
public class UserDTO {
private Long id;
private String username;
private String email;
// getters and setters
}
In this example, we have defined a `UserDTO` class that contains three fields: `id`, `username`, and `email`. We have also included getters and setters for each field, which allow us to access and modify the values of the fields.
To use this DTO in our Spring Boot application, we need to create an instance of the `UserDTO` class & populate it with data.
This is an example of how we might do this in a service layer method:
public UserDTO getUserById(Long id) {
User user = userRepository.findById(id).orElse(null);
if (user == null) {
return null;
}
UserDTO userDTO = new UserDTO();
userDTO.setId(user.getId());
userDTO.setUsername(user.getUsername());
userDTO.setEmail(user.getEmail());
return userDTO;
}
In this example, we have defined a `getUserById` method that takes a user ID as a parameter & returns a `UserDTO` object. We first retrieve the `User` object from the database using the `userRepository`. If the user is not found, we return `null`.
If the user is found, we create a new instance of the `UserDTO` class & populate it with data from the `User` object. We then return the `UserDTO` object to the caller.
Finally, we can use the `UserDTO` object in our presentation layer to display the user data to the client. Let’s see an example of how we might do this in a Spring MVC controller:
@GetMapping("/users/{id}")
public UserDTO getUser(@PathVariable Long id) {
return userService.getUserById(id);
}
In this example, we have defined a `getUser` method that maps to the `/users/{id}` URL path. We use the `@PathVariable` annotation to retrieve the `id` parameter from the URL & pass it to the `userService.getUserById` method to retrieve the `UserDTO` object.
The `UserDTO` object is then automatically serialized to JSON & returned to the client as the response body.
Frequently Asked Questions
Can DTOs contain business logic?
No, DTOs should not contain any business logic. They are simple objects used for transferring data between application layers.
How do DTOs differ from domain objects?
Domain objects contain business logic and represent the core entities of an application, while DTOs are used to transfer data and do not contain any business logic.
Can DTOs be used for data validation?
While DTOs can be used to validate data, it is generally recommended to keep validation logic separate from DTOs & perform validation in the service layer or using a separate validation framework.
Conclusion
In this article, we have learned about Data Transfer Objects (DTOs) and their role in Spring Boot applications. We explained DTOs, why they are used, and how to create them. DTOs provide a way to transfer data between different layers of an application in a clean and efficient manner while also offering benefits such as decoupling, data hiding, flexibility, performance, and versioning.
You can also check out our other blogs on Code360.
7+ registered 
