如何通过Spring WebFlux Integration为出站网关添加请求属性

出站网关XML配置如下： #

<outbound-gateway id="reactiveFullConfig"
              url="http://localhost:8080/hello"
              http-method="GET"
              request-channel="requests"
              reply-timeout="1234"
              extract-request-payload="false"
              expected-response-type="java.lang.String"
              mapped-request-headers="requestHeader1, requestHeader2"
              mapped-response-headers="responseHeader"
              reply-channel="replies"
              charset="UTF-8"
              order="77"
              auto-startup="false"
              transfer-cookies="true"
              reply-payload-to-flux="true"
              body-extractor="bodyExtractor"
              publisher-element-type-expression="headers.elementType"
              extract-response-body="false">
<uri-variable name="foo" expression="headers.bar"/>
</outbound-gateway>

需求：在请求发送到request通道前，为每个请求设置动态可变的request属性，效果等价于WebClient中通过.attribute()方法设置请求属性：

webClient.get().uri("http://localhost:8080/hello")
                .attribute("MYCUSTOMATTRIBUTE_1", "customvalue")
                .retrieve()
                .toEntity(String.class)
                .block()        
                .getBody();

当前发送请求的代码：

DirectChannel requestChannel = context.getBean("requestChannel", DirectChannel.class);
requestChannel.send(MessageBuilder.withPayload("Test message").build());

Spring WebFlux Integration是否提供类似WebClient .attribute()的实现方式？

另外，尝试通过消息头传递值，但ClientRequest中无法获取自定义头requestHeader1（已在mapped-request-headers中配置该头）：

requestChannel.send(MessageBuilder.withPayload("Test message").setHeader("requestHeader1","customvalue").build());

1. 利用request-configurer定制ClientRequest属性 #

Spring WebFlux Integration的WebClientOutboundGateway（对应XML中的<outbound-gateway>）支持通过ClientRequest.Builder定制请求，包括设置请求属性。核心是通过网关的request-configurer注入请求定制逻辑，从消息头中提取动态值并设置到ClientRequest。

方式一：XML配置直接内嵌SpEL定制逻辑

修改出站网关配置，添加request-configurer，通过SpEL从消息头读取属性值并设置到ClientRequest：

<outbound-gateway id="reactiveFullConfig"
              url="http://localhost:8080/hello"
              http-method="GET"
              request-channel="requests"
              reply-timeout="1234"
              extract-request-payload="false"
              expected-response-type="java.lang.String"
              mapped-request-headers="requestHeader1, requestHeader2"
              mapped-response-headers="responseHeader"
              reply-channel="replies"
              charset="UTF-8"
              order="77"
              auto-startup="false"
              transfer-cookies="true"
              reply-payload-to-flux="true"
              body-extractor="bodyExtractor"
              publisher-element-type-expression="headers.elementType"
              extract-response-body="false">
    <uri-variable name="foo" expression="headers.bar"/>
    <request-configurer>
        <bean class="org.springframework.integration.webflux.support.WebClientRequestConfigurer">
            <property name="requestCustomizer">
                <value>
                    builder -> builder.attribute('MYCUSTOMATTRIBUTE_1', headers['MYCUSTOMATTRIBUTE_1'])
                </value>
            </property>
        </bean>
    </request-configurer>
</outbound-gateway>

发送消息时在头中传入动态属性值：

DirectChannel requestChannel = context.getBean("requestChannel", DirectChannel.class);
requestChannel.send(MessageBuilder.withPayload("Test message")
        .setHeader("MYCUSTOMATTRIBUTE_1", "customvalue")
        .build());

方式二：自定义ClientRequestCustomizer实现复杂逻辑

如果需要更复杂的属性处理逻辑，比如从上下文中获取值，可以定义自定义的Function<ClientRequest.Builder, ClientRequest.Builder> Bean：

@Component("customAttributeRequestCustomizer")
public class CustomAttributeRequestCustomizer implements Function<ClientRequest.Builder, ClientRequest.Builder> {
    @Override
    public ClientRequest.Builder apply(ClientRequest.Builder builder) {
        // 获取当前处理的消息
        Message<?> currentMessage = IntegrationMessageHeaderAccessor.getCurrentMessage();
        if (currentMessage != null) {
            // 从消息头提取动态属性值
            String customValue = (String) currentMessage.getHeaders().get("MYCUSTOMATTRIBUTE_1");
            builder.attribute("MYCUSTOMATTRIBUTE_1", customValue);
        }
        return builder;
    }
}

然后在XML网关配置中引用该Bean：

<outbound-gateway id="reactiveFullConfig"
              ...
              request-configurer="customAttributeRequestCustomizer">
    ...
</outbound-gateway>

2. 解决自定义头无法获取的问题 #

你之前尝试通过消息头传递requestHeader1但在ClientRequest中拿不到，原因在于：

• mapped-request-headers的作用是将消息头映射为HTTP请求头，而非ClientRequest的属性。如果要获取HTTP头，可以通过ClientRequest.headers()访问；如果要设置ClientRequest的属性，必须使用上述request-configurer方式。
• 注意消息头名称的大小写：消息头是区分大小写的，确保设置和读取的头名称完全一致。

总结 #

Spring WebFlux Integration完全支持类似WebClient .attribute()的动态属性设置能力，通过request-configurer结合消息头传递动态值，即可为每个请求设置不同的ClientRequest属性。

内容的提问来源于stack exchange，提问作者ProblemSolver