Building Scalable REST APIs with Spring Boot

When building REST APIs that need to handle high traffic and scale horizontally, following proven architectural patterns and best practices is crucial. In this post, I'll share my experience building production-grade APIs with Spring Boot.

Core Principles

1. Layered Architecture

A well-structured API follows clear separation of concerns:

@RestController
@RequestMapping("/api/v1/products")
public class ProductController {
    
    private final ProductService productService;
    
    @GetMapping
    public ResponseEntity<Page<ProductDTO>> getAllProducts(
        @RequestParam(defaultValue = "0") int page,
        @RequestParam(defaultValue = "20") int size
    ) {
        return ResponseEntity.ok(productService.getAllProducts(page, size));
    }
}

2. DTO Pattern

Always use Data Transfer Objects to decouple your API contract from domain models:

public class ProductDTO {
    private Long id;
    private String name;
    private BigDecimal price;
    
    // Getters and setters
}

Performance Optimization

Database Query Optimization

Use JPA specifications and proper indexing:

@Repository
public interface ProductRepository extends JpaRepository<Product, Long>, JpaSpecificationExecutor<Product> {
    
    @Query("SELECT p FROM Product p WHERE p.category.id = :categoryId")
    Page<Product> findByCategoryId(@Param("categoryId") Long categoryId, Pageable pageable);
}

Caching Strategy

Implement caching with Spring Cache:

@Service
@CacheConfig(cacheNames = "products")
public class ProductServiceImpl implements ProductService {
    
    @Override
    @Cacheable(key = "#id")
    public ProductDTO getProductById(Long id) {
        // Implementation
    }
}

Security Best Practices

JWT Authentication

Implement stateless authentication with JWT:

@Configuration
@EnableWebSecurity
public class SecurityConfig {
    
    @Bean
    public SecurityFilterChain securityFilterChain(HttpSecurity http) throws Exception {
        return http
            .csrf(csrf -> csrf.disable())
            .sessionManagement(session -> session.sessionCreationPolicy(SessionCreationPolicy.STATELESS))
            .authorizeHttpRequests(auth -> auth
                .requestMatchers("/api/v1/auth/**").permitAll()
                .anyRequest().authenticated()
            )
            .addFilterBefore(jwtAuthenticationFilter, UsernamePasswordAuthenticationFilter.class)
            .build();
    }
}

Error Handling

Implement global exception handling:

@RestControllerAdvice
public class GlobalExceptionHandler {
    
    @ExceptionHandler(ResourceNotFoundException.class)
    public ResponseEntity<ErrorResponse> handleResourceNotFound(ResourceNotFoundException ex) {
        ErrorResponse error = new ErrorResponse(
            HttpStatus.NOT_FOUND.value(),
            ex.getMessage()
        );
        return new ResponseEntity<>(error, HttpStatus.NOT_FOUND);
    }
}

Conclusion

Building scalable REST APIs requires attention to architecture, performance, security, and maintainability. Spring Boot provides excellent tools for implementing these patterns effectively.

In future posts, I'll dive deeper into microservices architecture, event-driven systems, and advanced Spring Boot features.