Spring Boot 4 vs 3: Todo lo que Cambió y Cómo Migrar tu Proyecto

1<!-- Spring Boot 3: un solo starter lo traía TODO -->
2<dependency>
3    <groupId>org.springframework.boot</groupId>
4    <artifactId>spring-boot-starter-web</artifactId>
5</dependency>
6
7<!-- Spring Boot 4: starters modulares más granulares -->
8<dependency>
9    <groupId>org.springframework.boot</groupId>
10    <artifactId>spring-boot-starter-web</artifactId>
11</dependency>
12<!-- Los Classic Starter POMs siguen funcionando para compatibilidad -->
13<!-- Pero ahora puedes importar módulos individuales si prefieres -->

1@RestController
2@RequestMapping("/api/accounts")
3public class AccountController {
4
5    // Versión 1.0 — respuesta básica
6    @GetMapping(url = "/{id}", version = "1.0")
7    public AccountV1 getAccountV1(@PathVariable Long id) {
8        Account account = accountService.findById(id);
9        return new AccountV1(account.getId(), account.getName());
10    }
11
12    // Versión 2.0 — respuesta enriquecida con balance y metadata
13    @GetMapping(url = "/{id}", version = "2.0")
14    public AccountV2 getAccountV2(@PathVariable Long id) {
15        Account account = accountService.findById(id);
16        return new AccountV2(
17            account.getId(),
18            account.getName(),
19            account.getBalance(),
20            account.getMetadata()
21        );
22    }
23}

1@Configuration
2public class ApiVersionConfig implements WebMvcConfigurer {
3
4    @Override
5    public void configureApiVersioning(ApiVersionConfigurer configurer) {
6        configurer
7            .usePathPrefix("/api/v{version}")  // Estrategia por path
8            .defaultVersion("1.0")
9            .reportDeprecated(true);           // Avisa si usas versión deprecada
10    }
11}

1# application.yml — habilitar virtual threads
2spring:
3  threads:
4    virtual:
5      enabled: true

1@RestController
2@RequestMapping("/api/orders")
3public class OrderController {
4
5    private final OrderRepository orderRepository;
6    private final PaymentService paymentService;
7    private final NotificationService notificationService;
8
9    // Este endpoint BLOQUEA — pero con virtual threads, no importa.
10    // Cada request usa un virtual thread que apenas consume memoria.
11    @GetMapping("/{id}")
12    public OrderDetails getOrder(@PathVariable Long id) {
13        // Llamada bloqueante a DB — OK con virtual threads
14        Order order = orderRepository.findById(id).orElseThrow();
15
16        // Llamada bloqueante a servicio externo — OK con virtual threads
17        PaymentInfo payment = paymentService.getPayment(order.getPaymentId());
18
19        return new OrderDetails(order, payment);
20    }
21}

1@Service
2public class UserProfileService {
3
4    private final UserService userService;
5    private final OrderService orderService;
6    private final RecommendationService recommendationService;
7
8    public UserProfile buildProfile(Long userId) throws Exception {
9        try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
10            // Las 3 llamadas se ejecutan en paralelo, cada una en un virtual thread
11            var userTask = scope.fork(() -> userService.getUser(userId));
12            var ordersTask = scope.fork(() -> orderService.getOrdersForUser(userId));
13            var recsTask = scope.fork(() -> recommendationService.getForUser(userId));
14
15            scope.join();           // Espera a que todas terminen
16            scope.throwIfFailed();  // Si alguna falló, propaga la excepción
17
18            return new UserProfile(
19                userTask.get(),
20                ordersTask.get(),
21                recsTask.get()
22            );
23        }
24        // Si una falla, las demás se cancelan automáticamente
25    }
26}

1import org.jspecify.annotations.NonNull;
2import org.jspecify.annotations.Nullable;
3
4@Service
5public class UserService {
6
7    // El compilador te avisa si pasas null aquí
8    public @NonNull User findByEmail(@NonNull String email) {
9        return userRepository.findByEmail(email)
10            .orElseThrow(() -> new UserNotFoundException(email));
11    }
12
13    // Explícitamente puede retornar null
14    public @Nullable User findOptionalByEmail(@NonNull String email) {
15        return userRepository.findByEmail(email).orElse(null);
16    }
17}

1@Service
2@EnableResilientMethods
3public class PaymentGateway {
4
5    // Reintenta 3 veces con backoff exponencial
6    @Retryable(maxAttempts = 3, backoff = @Backoff(delay = 1000, multiplier = 2))
7    public PaymentResult processPayment(PaymentRequest request) {
8        return externalPaymentApi.charge(request);
9    }
10
11    // Limita la concurrencia a 10 llamadas simultáneas
12    @ConcurrencyLimit(permits = 10)
13    public Report generateHeavyReport(ReportParams params) {
14        return reportEngine.generate(params);
15    }
16}

1# application.yml — observabilidad completa con mínima config
2management:
3  tracing:
4    enabled: true
5    sampling:
6      probability: 1.0
7  otlp:
8    tracing:
9      endpoint: http://otel-collector:4318/v1/traces
10    metrics:
11      endpoint: http://otel-collector:4318/v1/metrics
12  endpoints:
13    web:
14      exposure:
15        include: health,info,metrics,prometheus

1<!-- pom.xml — cambio principal -->
2<parent>
3    <groupId>org.springframework.boot</groupId>
4    <artifactId>spring-boot-starter-parent</artifactId>
5    <!-- Antes: -->
6    <!-- <version>3.5.4</version> -->
7    <!-- Ahora: -->
8    <version>4.0.5</version>
9    <relativePath/>
10</parent>

1# Verifica compatibilidad con el migration guide
2# https://github.com/spring-projects/spring-boot/wiki/Spring-Boot-4.0-Migration-Guide
3
4# Compila y ejecuta tests
5./mvnw clean test
6
7# Si usas Moderne.io, la migración se puede automatizar:
8mod git clone moderne-io/spring-boot-4-migration
9mod run . --recipe SpringBoot4BestPractices