API Best Practices: The Ultimate Guide

Introduction

APIs (Application Programming Interfaces) act as bridges between different systems, enabling them to communicate. A well-designed API ensures scalability, maintainability, and security. This guide covers best practices for designing, developing, and maintaining APIs, particularly in Spring Boot.

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1. API Design Best Practices

1.1 Use RESTful Principles

• Use nouns in resource URLs (avoid verbs).
• Follow CRUD operations mapping:
  • GET /users → Fetch users
  • POST /users → Create a user
  • PUT /users/{id} → Update a user
  • DELETE /users/{id} → Delete a user

Bad API Design:

POST /createUser  
GET /fetchUserDetails?id=123  

Good API Design:

POST /users  
GET /users/123  

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1.2 Use Versioning

APIs evolve over time. Use versioning to ensure backward compatibility.

Approaches:

1. URI versioning: GET /v1/users
2. Query parameter: GET /users?version=1
3. Header-based versioning: Accept: application/vnd.myapi.v1+json

Best practice: Use URI versioning for simplicity.

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1.3 Use Proper HTTP Methods

HTTP Method	Purpose
GET	Retrieve a resource
POST	Create a resource
PUT	Update a resource (entire)
PATCH	Update a resource (partial)
DELETE	Remove a resource

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1.4 Use Consistent and Predictable Status Codes

Status Code	Meaning
200 OK	Successful request
201 Created	Resource created
204 No Content	No response body (DELETE)
400 Bad Request	Invalid input
401 Unauthorized	Authentication required
403 Forbidden	Insufficient permissions
404 Not Found	Resource not found
409 Conflict	Conflict (duplicate data)
500 Internal Server Error	Server-side issue

Example in Spring Boot:

@GetMapping("/{id}")
public ResponseEntity<User> getUser(@PathVariable Long id) {
    return ResponseEntity.ok(userService.getUserById(id));
}

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2. Response Handling & Error Management

2.1 Use Consistent JSON Responses

Return structured JSON responses instead of plain text messages.

Example:

{
  "timestamp": "2025-03-20T12:00:00Z",
  "status": 404,
  "error": "Not Found",
  "message": "User not found",
  "path": "/users/123"
}

Spring Boot Exception Handling:

@RestControllerAdvice
public class GlobalExceptionHandler {
    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<ErrorResponse> handleResourceNotFound(ResourceNotFoundException ex) {
        ErrorResponse error = new ErrorResponse(LocalDateTime.now(), 404, "Not Found", ex.getMessage());
        return ResponseEntity.status(HttpStatus.NOT_FOUND).body(error);
    }
}

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3. Pagination, Filtering, and Sorting

3.1 Pagination

Large datasets should be paginated to improve performance.

Example API Call:

GET /users?page=2&size=10

Spring Boot Implementation:

@GetMapping
public ResponseEntity<Page<User>> getUsers(Pageable pageable) {
    return ResponseEntity.ok(userService.getUsers(pageable));
}

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3.2 Sorting

Allow sorting results dynamically.

Example API Call:

GET /users?sort=name,asc

Spring Boot Implementation:

@GetMapping
public ResponseEntity<List<User>> getUsers(@RequestParam String sortBy) {
    List<User> users = userService.getUsersSorted(sortBy);
    return ResponseEntity.ok(users);
}

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3.3 Filtering

Allow filtering based on fields.

Example API Call:

GET /users?role=admin&active=true

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4. Security Best Practices

4.1 Use Authentication & Authorization

Implement OAuth2, JWT, or API keys to secure APIs.

Spring Security with JWT:

public class JwtRequestFilter extends OncePerRequestFilter {
    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain chain) {
        // Extract JWT, validate, and set authentication context
    }
}

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4.2 Avoid Exposing Sensitive Data

Mask passwords, tokens, or internal error messages in API responses.

Example:

{
  "id": 123,
  "username": "john_doe",
  "email": "hidden"
}

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4.3 Use HTTPS

Always enforce HTTPS to protect data in transit.

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4.4 Rate Limiting

Prevent abuse by setting API rate limits (e.g., 100 requests per minute).

Spring Boot Implementation (Bucket4j):

@Bean
public FilterRegistrationBean<RateLimitFilter> rateLimitFilter() {
    return new FilterRegistrationBean<>(new RateLimitFilter());
}

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5. API Caching for Performance

5.1 Use HTTP Caching Headers

• Cache-Control: Cache-Control: max-age=3600
• ETag: ETag: "abc123"

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5.2 Use Redis for Caching

@Cacheable(value = "users", key = "#id")
public User getUserById(Long id) {
    return userRepository.findById(id).orElseThrow();
}

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6. Logging & Monitoring

6.1 Centralized Logging

Use ELK Stack (Elasticsearch, Logstash, Kibana) or Grafana for log aggregation.

private static final Logger LOGGER = LoggerFactory.getLogger(UserController.class);

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

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6.2 API Metrics & Monitoring

Use Spring Boot Actuator for monitoring API health.

Enable Actuator Endpoints:

management:
  endpoints:
    web:
      exposure:
        include: health,metrics

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7. API Documentation

Use Swagger for API documentation.

Add Swagger Dependency:

<dependency>
    <groupId>org.springdoc</groupId>
    <artifactId>springdoc-openapi-starter-webmvc-ui</artifactId>
    <version>2.0.0</version>
</dependency>

Access API Docs:

http://localhost:8080/swagger-ui.html

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Conclusion

By following these best practices, your APIs will be:

✅ Scalable

✅ Secure

✅ Maintainable

✅ Performant

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