Spring Boot Best Practices: Use DTOs Instead of Entities in API Responses

Learn why exposing JPA entities is bad and how to use DTOs in Spring Boot for secure, optimized APIs.

When building REST APIs in Spring Boot, many developers directly return JPA entities in API responses.

This may seem easy, but it’s a bad practice because it can:
❌ Expose sensitive fields (Security risk)
❌ Cause lazy loading issues (Performance impact)
❌ Tightly couple database structure with the API

💡 Solution? Use DTOs (Data Transfer Objects) instead of entities in responses.

In this guide, you’ll learn:
✅ Why exposing JPA entities is dangerous
✅ How DTOs improve API security and performance
✅ How to combine multiple entities into a single DTO
✅ A complete Spring Boot example with best practices

🚨 Problem: Exposing Entities Can Leak Sensitive Data

Let’s say we have a User entity representing database records:

@Entity
@Table(name = "users")
public class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String username;
    private String email;
    private String password; // 🚨 Sensitive data…