Spring

The N+1 problem is a common performance issue in JPA. Here’s how to solve it in Spring Data JPA. Understanding N+1 Problem // N+1 queries: 1 for users + N for each user's posts List<User> users = userRepository.findAll(); for (User user : users) { List<Post> posts = postRepository.findByUserId(user.getId()); // N queries } Solutions 1. Eager Fetching @Entity public class User { @OneToMany(fetch = FetchType.EAGER) private List<Post> posts; } 2. Join Fetch (JPQL) @Query("SELECT u FROM User u JOIN FETCH u.posts") List<User> findAllWithPosts(); 3. Entity Graphs @EntityGraph(attributePaths = {"posts"}) @Query("SELECT u FROM User u") List<User> findAllWithPosts(); 4. Batch Fetching @Entity public class User { @BatchSize(size = 10) @OneToMany(fetch = FetchType.LAZY) private List<Post> posts; } Best Practices Use lazy loading by default Fetch associations when needed Use entity graphs Monitor query performance Use DTO projections Conclusion Solve N+1 problems with: ...

Spring WebFlux enables reactive programming in Spring. Here’s when and how to use it. When to Use WebFlux Use WebFlux When: High concurrency requirements Non-blocking I/O needed Streaming data Microservices with reactive backends Use MVC When: Traditional request-response Blocking operations Existing Spring MVC codebase Simpler mental model needed Basic Setup Dependencies <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-webflux</artifactId> </dependency> Reactive Controller @RestController public class UserController { @GetMapping("/users") public Flux<User> getUsers() { return userService.findAll(); } @GetMapping("/users/{id}") public Mono<User> getUser(@PathVariable Long id) { return userService.findById(id); } @PostMapping("/users") public Mono<User> createUser(@RequestBody Mono<User> user) { return userService.save(user); } } Reactive Types Mono // Single value or empty Mono<String> mono = Mono.just("Hello"); Mono<String> empty = Mono.empty(); Mono<String> error = Mono.error(new RuntimeException()); Flux // Multiple values Flux<String> flux = Flux.just("A", "B", "C"); Flux<Integer> range = Flux.range(1, 10); Reactive Repository public interface UserRepository extends ReactiveCrudRepository<User, Long> { Flux<User> findByStatus(String status); Mono<User> findByEmail(String email); } Error Handling @GetMapping("/users/{id}") public Mono<User> getUser(@PathVariable Long id) { return userService.findById(id) .switchIfEmpty(Mono.error(new UserNotFoundException())) .onErrorResume(error -> { // Handle error return Mono.empty(); }); } Testing @SpringBootTest @AutoConfigureWebTestClient class UserControllerTest { @Autowired private WebTestClient webTestClient; @Test void shouldGetUsers() { webTestClient.get() .uri("/users") .exchange() .expectStatus().isOk() .expectBodyList(User.class); } } Best Practices Use reactive types throughout Avoid blocking operations Handle errors properly Use backpressure Monitor performance Conclusion Spring WebFlux provides: ...