Yapılandırılmış Loglama — Gece 2'de Doğru Satırı Bulmak

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logging:
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  structured:
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    format:
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      console: ecs          # one JSON object per line (Spring Boot 3.4+)
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  level:
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    root: INFO
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    com.bank.transfer: INFO
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management:
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  tracing:
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    sampling:
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      probability: 1.0      # traceId and spanId are added to every log line

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// Adds the authenticated customer to every log line of this request, and
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// removes it afterwards so a pooled thread does not carry it into the next one.
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// The id comes from the principal Spring Security set, never from a client header.
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@Component
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class CustomerLogContext implements HandlerInterceptor {
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    @Override
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    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) {
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        Principal principal = request.getUserPrincipal();
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        if (principal != null) MDC.put("customerId", principal.getName());
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        return true;
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    }
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    @Override
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    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) {
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        MDC.remove("customerId");
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    }
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}

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// Whatever logs an Iban gets the masked form; the full value needs an explicit call.
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public record Iban(String value) {
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    public Iban {
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        Objects.requireNonNull(value);
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    }
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    public String full() {
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        return value;
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    }
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    @Override
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    public String toString() {
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        return value.substring(0, 4) + "****" + value.substring(value.length() - 4);
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    }
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}

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@Service
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class TransferService {
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    private static final Logger log = LoggerFactory.getLogger(TransferService.class);
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    private final Ledger ledger;
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    TransferService(Ledger ledger) {
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        this.ledger = ledger;
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    }
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    TransferResult send(TransferRequest request) {
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        try {
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            return ledger.post(request);
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        } catch (LedgerTimeoutException ex) {
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            // The exception goes last: the stack trace is kept. The IBAN prints masked.
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            log.error("transfer failed transferId={} to={}", request.id(), request.to(), ex);
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            throw new TransferFailedException(request.id(), ex);
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        }
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    }
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}