Part 6 · 1 chapters · ~8 min

Spring Boot End to End

Starters and auto-configuration, application.yml and profiles, REST controllers with records and validation, ProblemDetail errors, Spring Data JPA and Hibernate, transactions, Spring Security with JWT resource servers, Flyway migrations, Actuator health and metrics, and virtual threads.

A Spring Boot service

code

@RestController @RequestMapping("/v1/transfers")
class TransferController {
    private final TransferService service;
    TransferController(TransferService service) { this.service = service; }

    record CreateTransfer(@Positive long amountKobo, @NotBlank String to) {}

    @PostMapping @ResponseStatus(HttpStatus.CREATED)
    TransferView create(@Valid @RequestBody CreateTransfer in, @RequestHeader("Idempotency-Key") String key, @AuthenticationPrincipal Jwt jwt) {
        return service.create(jwt.getSubject(), in.amountKobo(), in.to(), key);
    }
}

@RestControllerAdvice
class Errors {
    @ExceptionHandler(InsufficientFundsException.class)
    ProblemDetail insufficient(InsufficientFundsException e) { return ProblemDetail.forStatusAndDetail(HttpStatus.UNPROCESSABLE_ENTITY, e.getMessage()); }
}

# application.yml
spring:
  threads.virtual.enabled: true
  datasource: { url: jdbc:postgresql://db/ledger, hikari: { maximum-pool-size: 20 } }
  jpa: { open-in-view: false }                    # never keep sessions open across the whole request
  security.oauth2.resourceserver.jwt.issuer-uri: https://auth.bank.example
management.endpoints.web.exposure.include: health,info,prometheus

A SPRING BOOT REQUEST

DispatcherServlet to controller to service to repository, with Spring wiring everything

swipe the figure sideways, or tap expand for full screen

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the server

Spring Boot embeds Tomcat (or Jetty, Undertow, Netty for WebFlux) in an executable jar; with virtual threads enabled, each request runs on a virtual thread.

embedded server in a fat jarjava -jar ledger.jar