log configuration

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logging:
  pattern:
    console: "%d{yyyy-MM-dd} %d{HH:mm:ss.SSS} %clr(%5p) %clr(%-40.40logger{39}) :[%8X{tenant}] %m%n${LOG_EXCEPTION_CONVERSION_WORD:%rEx}"

logutil class

public final class LogUtil {

  private LogUtil() {
  }

  public static <T> Consumer<Signal<T>> logOnNext(Consumer<T> logStatement) {
    return signal -> {
      if (!signal.isOnNext())
        return;
      Optional<String> optionalTenant = signal.getContext().getOrEmpty("TENANT_CONTEXT");
      optionalTenant.ifPresentOrElse(tenant -> {
        try (MDC.MDCCloseable closeable = MDC.putCloseable("tenant", tenant)) {
          logStatement.accept(signal.get());
        }
      }, () -> logStatement.accept(signal.get()));

    };
  }

  public static <T> Consumer<Signal<T>> logOnError(Consumer<Throwable> logStatement) {
    return signal -> {
      if (!signal.isOnError())
        return;
      Optional<String> optionalTenant = signal.getContext().getOrEmpty("TENANT_CONTEXT");
      optionalTenant.ifPresentOrElse(tenant -> {
        try (MDC.MDCCloseable closeable = MDC.putCloseable("tenant", tenant)) {
          logStatement.accept(signal.getThrowable());
        }
      }, () -> logStatement.accept(signal.getThrowable()));
    };
  }

  public static <T> Consumer<Signal<T>> logOnComplete(Consumer<T> logStatement) {
    return signal -> {
      if (!signal.isOnComplete())
        return;
      Optional<String> optionalTenant = signal.getContext().getOrEmpty("TENANT_CONTEXT");
      optionalTenant.ifPresentOrElse(tenant -> {
        try (MDC.MDCCloseable closeable = MDC.putCloseable("tenant", tenant)) {
          logStatement.accept(signal.get());
        }
      }, () -> logStatement.accept(signal.get()));

    };
  }

}

populating the context

public class TenancyContextFilter implements WebFilter {

  @Override
  public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
    String tenantAlias = extractTenantAliasFromRequest(exchange.getRequest());
    if (tenantAlias != null) {
      return chain.filter(exchange)
                .subscriberContext(context -> {
                  return context.put("TENANT_CONTEXT", tenantAlias);
                });
    } else {
      LOGGER.error(...);
      return Mono.error(new TenantExtractionException());
    }
  }

}

usage

someMono
  .doOnEach(LogUtil.logOnNext(obj -> logger.info(...)))
  
someMono
  .doOnEach(LogUtil.logOnComplete(obj -> logger.info(...)))
  
someMono
  .doOnEach(LogUtil.logOnError(err -> logger.error(...)))

Webflux MDC Logging.md

A technique to do MDC logging in reactive JAVA web application using Spring.

An example demonstrating printing of tenant id as mdc in logs.