Top 10 REST API Mistakes and How to Avoid Them

REST APIs help different applications communicate with each other. Web, mobile, and cloud applications use them to exchange data smoothly. However, many developers make mistakes while building APIs, leading to slow performance, security issues, and difficult maintenance. Fixing these problems early makes APIs faster, safer, and easier to use.

In this article, we will go through the top 10 common mistakes in REST API development and how to avoid them. These mistakes include using incorrect HTTP status codes, not securing the API properly, returning too much data, and ignoring proper error handlingThese issues can cause API failures, security risks, and bad user experiences if not fixed.

You can create well-structured, efficient, and secure REST APIs by understanding these mistakes and following best practices. Let’s go step by step and learn how to improve your API design and make it work smoothly. 🚀

1️⃣ Ignoring Proper HTTP Status Codes

Mistake: Returning 200 for Everything

Some developers return 200 OK for every response, even when an error occurs. This makes it hard to debug issues on the client side.

{
    "status": "error",
    "message": "User not found"
}

Solution: Use Correct HTTP Status Codes

Each response should use the appropriate status code:

HTTP Status Code Meaning When to Use
200 OK Success When a request is processed successfully
201 Created Resource Created When a new resource is created
400 Bad Request Invalid Input When the client sends incorrect data
401 Unauthorized Authentication Required When the request lacks valid credentials
403 Forbidden No Permission When the user lacks access rights
404 Not Found Resource Not Found When a requested resource doesn’t exist
500 Internal Server Error Server Crash When an unexpected error occurs

Example (Correct Implementation)

@GetMapping("/users/{id}")
public ResponseEntity<User> getUser(@PathVariable Long id) {
    return userService.findById(id)
        .map(user -> ResponseEntity.ok(user))
        .orElseGet(() -> ResponseEntity.status(HttpStatus.NOT_FOUND).build());
}

2️⃣ Poorly Designed API Endpoints

Mistake: Using Non-RESTful URIs

APIs should be predictable and follow RESTful conventions.

Bad URI design:

/getUser?id=10
/createNewUser
/updateUser/10

Solution: Follow RESTful Naming Conventions

  • Use nouns, not verbs
    /users (Get all users)
    /users/{id} (Get user by ID)
    /users/{id}/orders (Get user’s orders)
    /users/{id}/delete(Wrong - Use DELETE method)

Example

@DeleteMapping("/users/{id}")
public ResponseEntity<Void> deleteUser(@PathVariable Long id) {
    userService.deleteUser(id);
    return ResponseEntity.noContent().build();
}

3️⃣ Exposing Sensitive Data in API Responses

Mistake: Returning Passwords & Tokens in Responses

Never expose sensitive information like passwords, API keys, or internal server errors.

{
    "id": 1,
    "email": "user@example.com",
    "password": "mypassword123"
}

Solution: Use DTOs to Control Data Exposure

Use DTO (Data Transfer Objects) to restrict the fields being sent.

Example

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

4️⃣ Not Implementing Proper Authentication & Authorization

Mistake: Open API Endpoints

A public API without authentication allows anyone to access sensitive data.

@GetMapping("/admin/users")
public List<User> getAllUsers() {
    return userService.getAllUsers();  // ❌ No security check
}

Solution: Secure API with JWT & OAuth2

Example: Secure APIs with JWT Authentication

@Configuration
@EnableWebSecurity
public class SecurityConfig {
    @Bean
    public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
        http.authorizeHttpRequests(auth -> auth.anyRequest().authenticated())
            .oauth2ResourceServer(OAuth2ResourceServerConfigurer::jwt);
        return http.build();
    }
}

5️⃣ Not Using Pagination for Large Data Sets

Mistake: Returning All Data in One Response

@GetMapping("/users")
public List<User> getAllUsers() {
    return userRepository.findAll();  // ❌ Can crash the server if millions of records exist
}

Solution: Implement Pagination

@GetMapping("/users")
public Page<User> getUsers(Pageable pageable) {
    return userRepository.findAll(pageable);
}

Benefits

  • Improves performance
  • Prevents timeouts
  • Optimized for large datasets

6️⃣ Ignoring Proper Exception Handling

Mistake: Exposing Internal Errors

A bad API simply throws raw exceptions, exposing internal details.

@GetMapping("/users/{id}")
public User getUser(@PathVariable Long id) {
    return userRepository.findById(id).get();  // ❌ Throws 500 Internal Server Error
}

Solution: Use Global Exception Handling

@RestControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<String> handleNotFound(ResourceNotFoundException ex) {
        return ResponseEntity.status(HttpStatus.NOT_FOUND).body(ex.getMessage());
    }
}

Benefits

  • Consistent error responses
  • Hides sensitive error messages

7️⃣ Using RestTemplate Instead of RestClient

Mistake: Using Deprecated RestTemplate

RestTemplate restTemplate = new RestTemplate();
User user = restTemplate.getForObject("https://api.example.com/user/1", User.class);

Solution: Use RestClient

RestClient restClient = RestClient.builder().baseUrl("https://api.example.com").build();
User user = restClient.get().uri("/user/1").retrieve().body(User.class);

Why is this better?

  • Better error handling
  • Asynchronous capabilities

8️⃣ Not Validating Input Data

Mistake: Accepting Unvalidated Input

@PostMapping("/users")
public ResponseEntity<String> createUser(@RequestBody User user) {
    return ResponseEntity.ok("User Created");
}

Risk: SQL Injection, Invalid Data, Security Issues

Solution: Use Validation Annotations

public record UserDTO(@NotBlank String name, @Email String email) {}
@PostMapping("/users")
public ResponseEntity<String> createUser(@Valid @RequestBody UserDTO userDTO) {
    return ResponseEntity.ok("User created successfully");
}

Benefits

  • Prevents invalid data entry
  • Improves API security

9️⃣ Not Logging API Requests & Errors

Mistake: No Logging

Without logs, troubleshooting API failures is difficult.

Solution: Use Slf4j for Logging

@Slf4j
@RestController
@RequestMapping("/users")
public class UserController {

    @GetMapping("/{id}")
    public ResponseEntity<UserDTO> getUser(@PathVariable Long id) {
        log.info("Fetching user with id: {}", id);
        return ResponseEntity.ok(userService.getUserById(id));
    }
}

Benefits

  • Helps in debugging API failures
  • Tracks usage patterns

🔟 Ignoring API Documentation (Swagger UI)

Mistake: No API Documentation

Without documentation, developers struggle to use the API.

Solution: Use Swagger UI

<dependency>
    <groupId>org.springdoc</groupId>
    <artifactId>springdoc-openapi-starter-webmvc-ui</artifactId>
    <version>2.8.3</version>
</dependency>

Benefits

  • Self-explanatory APIs
  • Easier client integration

🎯 Conclusion

Building a robust REST API requires following best practices. Here’s a quick recap:

Use proper HTTP status codes
Secure your API with authentication
Implement pagination for performance
Validate all user inputs
Use DTOs instead of exposing entities
Handle exceptions globally
Use logging for debugging

By avoiding these mistakes, you can build scalable, secure, and high-performance APIs! 🚀

🔑 Keywords:

REST API mistakes, API best practices, Spring Boot API, Secure API, RESTful API optimization, Exception Handling, API Logging

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