如何在Spring Integration中从外部解析和获取headers属性值

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-integration</artifactId>
</dependency>

IntegrationFlow flow = IntegrationFlows.from("inputChannel")
    .handle("messageHandler", "handleMessage")
    .get();

@Component
public class MessageHandler implements MessageHandler {
    @Override
    public void handleMessage(Message<?> message) throws MessagingException {
        MessageHeaders headers = message.getHeaders();
        // 解析和获取headers属性值
        String value = (String) headers.get("headerName");
        // 处理消息
        // ...
    }
}

IntegrationFlow flow = IntegrationFlows.from("inputChannel")
    .handle("messageHandler", "handleMessage")
    .get();

@Autowired
private IntegrationFlowContext flowContext;

@Bean
public IntegrationFlowRegistration flowRegistration() {
    IntegrationFlow flow = IntegrationFlows.from("inputChannel")
        .handle("messageHandler", "handleMessage")
        .get();
    return this.flowContext.registration(flow).register();
}