🛠️ 15 Spring Boot REST API Pitfalls You Must Avoid

Many developers think their Spring Boot REST APIs are already well-implemented, but subtle mistakes can cause performance issues, security vulnerabilities, and maintenance headaches. In this post, I’ll share 15 common pitfalls and practical tips to build APIs that are fast, secure, and maintainable.

1. 📝 Proper Exception Handling

Returning raw exceptions or inconsistent error responses confuses API clients. Use @ControllerAdvice to centralize exception handling.

@ControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(Exception.class)
    public ResponseEntity<ApiError> handleException(Exception ex) {
        ApiError apiError = new ApiError(HttpStatus.INTERNAL_SERVER_ERROR, ex.getMessage());
        return new ResponseEntity<>(apiError, HttpStatus.INTERNAL_SERVER_ERROR);
    }
}

✅ Ensures clients get clear, consistent error messages and avoids exposing stack traces

2. 🔢 Validate Input Data

Skipping input validation leads to errors or security issues. Use @Valid and Bean Validation annotations.

@PostMapping("/users")
public ResponseEntity<User> createUser(@Valid @RequestBody User user) {
    User savedUser = userService.save(user);
    return new ResponseEntity<>(savedUser, HttpStatus.CREATED);
}

✅ Prevents invalid data from reaching your service layer or database

3. 📄 Pagination and Filtering

Exposing large datasets without pagination slows down your API. Always implement paging and filtering.

@GetMapping("/products")
public ResponseEntity<List<Product>> getProducts(
    @RequestParam(defaultValue = "0") int page,
    @RequestParam(defaultValue = "10") int size) {
    Page<Product> products = productService.getAll(page, size);
    return new ResponseEntity<>(products.getContent(), HttpStatus.OK);
}

✅ Improves performance and ensures clients can handle responses easily

4. ⚡ Avoid Blocking Calls

Blocking operations reduce scalability. For high-throughput endpoints, consider reactive programming with Spring WebFlux.

@GetMapping("/async-data")
public Mono<String> getAsyncData() {
    return Mono.just("Async Data");
}

✅ Enables APIs to handle more concurrent requests efficiently

5. 🔒 Secure Endpoints Properly

Never expose sensitive APIs without authentication. Use Spring Security with JWT or OAuth2.

@EnableWebSecurity
public class SecurityConfig extends WebSecurityConfigurerAdapter {
    @Override
    protected void configure(HttpSecurity http) throws Exception {
        http.csrf().disable()
            .authorizeRequests()
            .antMatchers("/public/**").permitAll()
            .anyRequest().authenticated()
            .and()
            .addFilter(new JwtAuthenticationFilter(authenticationManager()));
    }
}

✅ Protects endpoints from unauthorized access

6. 🏗️ Keep Controllers Thin

Controllers should handle HTTP mapping only. Business logic belongs in service layers.

@RestController
@RequestMapping("/users")
public class UserController {
    private final UserService userService;

    @Autowired
    public UserController(UserService userService) {
        this.userService = userService;
    }

    @GetMapping("/{id}")
    public ResponseEntity<User> getUser(@PathVariable Long id) {
        User user = userService.findById(id);
        return new ResponseEntity<>(user, HttpStatus.OK);
    }
}

✅ Easier to test and maintain

7. 📦 Version Your API

APIs evolve. Without versioning, changes may break clients.

@GetMapping("/v1/users")
public ResponseEntity<List<User>> getUsersV1() { ... }

@GetMapping("/v2/users")
public ResponseEntity<List<User>> getUsersV2() { ... }

✅ Maintains backward compatibility

8. 📝 Logging and Monitoring

@Slf4j
@RestController
@RequestMapping("/users")
public class UserController {
    @GetMapping("/{id}")
    public ResponseEntity<User> getUser(@PathVariable Long id) {
        log.info("Fetching user with id {}", id);
        User user = userService.findById(id);
        return new ResponseEntity<>(user, HttpStatus.OK);
    }
}

✅ Helps diagnose problems quickly and improves observability

9. 📚 Document Your API

Use Springdoc OpenAPI / Swagger for interactive documentation.

springdoc:
  api-docs:
    path: /v3/api-docs
  swagger-ui:
    path: /swagger-ui.html

✅ Makes API easy to integrate and test for developers

10. 🗂️ Returning Entities Directly

Returning JPA entities exposes internal fields and may trigger lazy-loading issues. Use DTOs instead.

@GetMapping("/users/{id}")
public UserDto getUser(@PathVariable Long id) {
    User user = userRepository.findById(id).orElseThrow();
    return new UserDto(user.getId(), user.getName(), user.getEmail());
}

✅ Keeps API decoupled and secure

11. 🔄 Overusing @Transactional in Controllers

✅ Keep transactions in service layer, not controllers

12. 💨 Ignoring Lazy Loading Issues

✅ Avoid exposing lazy relationships directly; use DTOs, @JsonIgnore, or fetch joins

13. 🔧 Hardcoding URLs or Endpoints

✅ Externalize configurations via application.properties or @Value

14. 🧩 Not Using DTOs for Updates

✅ Prevent accidental data corruption

15. 🔒 Ignoring Security Headers & CORS

✅ Configure Spring Security and CORS to protect APIs and clients

Conclusion

Avoiding these 15 common mistakes ensures your Spring Boot REST APIs are performant, secure, and maintainable. **Validate inputs, use DTOs, handle exceptions, secure endpoints, and document your API.**

Labels: Spring Boot, REST API, Best Practices, Java, Web Development, DTOs, Security, Performance