有人能帮我设置一下吗 KafkaHeaders.MESSAGE_KEY 下面的代码，以便我可以发布到不同的分区有效负载。

@Bean
public IntegrationFlow fileInboundChannelFlow() {
    FileInboundChannelAdapterSpec messageSourceSpec = Files
            .inboundAdapter(Paths.get(this.properties.getDirectory()).toFile());

    messageSourceSpec = messageSourceSpec.filter(getFilter());
    //messageSourceSpec.regexFilter(this.properties.getFilenameRegex());
    messageSourceSpec.preventDuplicates(this.properties.isPreventDuplicates());

    IntegrationFlowBuilder flowBuilder = IntegrationFlows.from(messageSourceSpec)
            .split(new FileSplitter(true, true))
            .enrichHeaders(h -> h.header(KafkaHeaders.MESSAGE_KEY, "payload.flightNumber"));

    return flowBuilder.<Object, Class<?>>route(Object::getClass,
            m -> m.channelMapping(FileSplitter.FileMarker.class, "markers.input").channelMapping(String.class,
                    "lines.input"))
            .get();
}

我想根据payload.prod\u cd设置密钥。因为是单例bean，所以我想为每个负载初始化不同的kafka头键。