🛠️ 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. Always use @ControllerAdvice to centralize exception handling and return consistent messages.

@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 receive clear, consistent error messages and avoids exposing internal stack traces.

2. 🔢 Validate Input Data

Skipping input validation leads to unexpected 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 and overloads clients. 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 the response 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 your API to handle more concurrent requests efficiently.

5. 🔒 Secure Endpoints Properly

Never expose sensitive APIs without authentication. Use Spring Security with JWT or OAuth2 for proper access control.

@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 your endpoints from unauthorized access and keeps sensitive data safe.

6. 🏗️ Keep Controllers Thin

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

@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);
    }
}

✅ Makes your API easier to test and maintain over time.

7. 📦 Version Your API

APIs evolve. Without versioning, changes may break existing clients. Use URI or header-based versioning.

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

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

✅ Helps manage backward compatibility as your API evolves.

8. 📝 Logging and Monitoring

Logs are critical for debugging and monitoring. Avoid logging sensitive info, and consider structured logs for observability.

@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 operational visibility.

9. 📚 Document Your API

APIs without documentation are hard for clients to consume. Use Springdoc OpenAPI / Swagger to generate interactive documentation.

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

✅ Makes your API easy to integrate and test for developers.

10. 🗂️ Returning Entities Directly

Returning JPA entities exposes internal fields, can trigger lazy-loading issues, and couples API to database. 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

Placing @Transactional on controllers can trigger lazy-loading exceptions and long-running transactions. Keep transactions in the service layer.

✅ Controllers should delegate, services handle transactions.

12. 💨 Ignoring Lazy Loading Issues

Returning entities with lazy-loaded associations can trigger N+1 queries or serialization errors. Use @JsonIgnore, DTOs, or fetch joins.

✅ Avoid exposing lazy relationships directly.

13. 🔧 Hardcoding URLs or External Endpoints

Hardcoded endpoints make testing and deployments harder. Use configuration (application.properties) or @Value.

✅ Always externalize configurations.

14. 🧩 Not Using DTOs for Updates

Accepting entities for updates can overwrite unintended fields. Use update DTOs for controlled updates.

✅ Prevents accidental data corruption.

15. 🔒 Ignoring Security Headers and CORS

Missing proper HTTP headers or misconfigured CORS can open security holes. Always configure Spring Security and CORS.

✅ Protect your API and clients from attacks.

Conclusion

Avoiding these 15 common mistakes ensures your Spring Boot REST APIs are performant, secure, and maintainable. Remember: **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