spring-boot-web-api

Spring Boot Web API Layer

REST API implementation patterns for Spring Boot 4 with Spring MVC and WebFlux.

Technology Selection

Choose	When
Spring MVC	JPA/JDBC backend, simpler debugging, team knows imperative style
Spring WebFlux	High concurrency (10k+ connections), streaming, reactive DB (R2DBC)

With Virtual Threads (Java 21+), MVC handles high concurrency without WebFlux complexity.

Core Workflow

1. Create controller → 2. Define endpoints → 3. Add validation → 4. Handle exceptions → 5. Configure versioning

See WORKFLOW.md for detailed step-by-step instructions with code examples.

Quick Patterns

See EXAMPLES.md for complete working examples including:

• REST Controller with CRUD operations and pagination (Java + Kotlin)
• Request/Response DTOs with Bean Validation 3.1
• Global Exception Handler using ProblemDetail (RFC 9457)
• Native API Versioning with header configuration
• Jackson 3 Configuration for custom serialization
• Controller Testing with @WebMvcTest

Spring Boot 4 Specifics

• Jackson 3 uses tools.jackson package (not com.fasterxml.jackson)
• ProblemDetail enabled by default: spring.mvc.problemdetails.enabled=true
• API Versioning via version attribute in mapping annotations
• @MockitoBean replaces @MockBean in tests
• @HttpExchange declarative HTTP clients (replaces RestTemplate patterns)
• RestTestClient new fluent API for testing REST endpoints

@HttpExchange Declarative Client (Spring 7)

New declarative HTTP client interface (alternative to RestTemplate/WebClient):

@HttpExchange(url = "/users", accept = "application/json")
public interface UserClient {

    @GetExchange("/{id}")
    User getUser(@PathVariable Long id);

    @PostExchange
    User createUser(@RequestBody CreateUserRequest request);

    @DeleteExchange("/{id}")
    void deleteUser(@PathVariable Long id);
}

// Configuration
@Configuration
class ClientConfig {
    @Bean
    UserClient userClient(RestClient.Builder builder) {
        RestClient restClient = builder.baseUrl("https://api.example.com").build();
        return HttpServiceProxyFactory
            .builderFor(RestClientAdapter.create(restClient))
            .build()
            .createClient(UserClient.class);
    }
}