getServiceClass example

        $definitions = [];
        $handlersByBusAndMessage = [];
        $handlerToOriginalServiceIdMapping = [];

        foreach ($container->findTaggedServiceIds('messenger.message_handler', true) as $serviceId => $tags) {
            foreach ($tags as $tag) {
                if (isset($tag['bus']) && !\in_array($tag['bus'], $busIds, true)) {
                    throw new RuntimeException(sprintf('Invalid handler service "%s": bus "%s" specified on the tag "messenger.message_handler" does not exist (known ones are: "%s").', $serviceId, $tag['bus'], implode('", "', $busIds)));
                }

                $className = $this->getServiceClass($container, $serviceId);
                $r = $container->getReflectionClass($className);

                if (null === $r) {
                    throw new RuntimeException(sprintf('Invalid service "%s": class "%s" does not exist.', $serviceId, $className));
                }

                if (isset($tag['handles'])) {
                    $handles = isset($tag['method']) ? [$tag['handles'] => $tag['method']] : [$tag['handles']];
                } else {
                    $handles = $this->guessHandledClasses($r, $serviceId, $tag['method'] ?? '__invoke');
                }