spring_boot

Create @RestController classes with proper HTTP method mappings, DTOs for requests and responses, and a service layer with constructor injection. Add @Valid for input validation and @RestControllerAdvice for global exception handling.

Configure a SecurityFilterChain bean with OAuth2 resource server support for JWT validation. Define authorization rules per endpoint and avoid deprecated WebSecurityConfigurerAdapter patterns from Spring Security 5.

Yes, Spring Boot 3.2+ supports Java 21 virtual threads via spring.threads.virtual.enabled=true. This improves throughput for high-concurrency blocking workloads without rewriting code to reactive style.

Use constructor injection instead of @Autowired on fields. Constructor injection makes dependencies explicit, enables final fields, simplifies unit testing, and prevents circular dependency issues at runtime.

Use test slices like @DataJpaTest for repositories and @WebMvcTest for controllers to run fast, isolated tests. For full integration tests with real databases, combine @SpringBootTest with Testcontainers.

Avoid calling blocking APIs (like JPA or RestTemplate) inside reactive WebFlux pipelines, as it defeats the non-blocking model and can exhaust threads. Choose one stack per service or isolate blocking work on dedicated schedulers.