WebClient plugin throws NPE

[wh88725]

JDK: 17
SpringBoot: 3.4.5
Webclient: 6.2.6
skywalking java agent: 9.5.0

I had copy the apm-spring-webflux-6.x-plugin-9.5.0.jar to plugins dir. And exclude spring-webflux-5.x-webclient-plugin-9.5.0.jar from plugins dir.
When I use webclient send requests, the agent throw NPE and log in agent log file.

How I use WebClient:
webClient.post().uri().headers().body().retrieve().bodyToFlux(String.class)

Stack:
ERROR 2025-11-20 17:09:06.511 otn-io-thread-1 InstMethodsInter : class[class org.springframework.web.reactive.function.client.DefaultClientRequestBuilder$BodyInserterRequest] before method[writeTo] intercept failure
java.lang.NullPointerException: Cannot invoke "org.apache.skywalking.apm.agent.core.context.ContextCarrier.items()" because "contextCarrier" is null
at org.apache.skywalking.apm.plugin.spring.webflux.v6.webclient.BodyInserterRequestInterceptor.beforeMethod(BodyInserterRequestInterceptor.java:37)
at org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.InstMethodsInter.intercept(InstMethodsInter.java:83)
at org.springframework.web.reactive.function.client.DefaultClientRequestBuilder$BodyInserterRequest.writeTo(DefaultClientRequestBuilder.java)
at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.lambda$exchange$1(ExchangeFunctions.java:103)
at org.springframework.http.client.reactive.JdkClientHttpConnector.connect(JdkClientHttpConnector.java:117)
at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.$sw$original$exchange$1duusa0(ExchangeFunctions.java:103)
at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.$sw$original$exchange$1duusa0$accessor$$sw$fl9sv53(ExchangeFunctions.java)
at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction$$sw$auxiliary$uv3mfs1.call(Unknown Source)
at org.apache.skywalking.apm.agent.core.plugin.interceptor.enhance.v2.InstMethodsInterV2.intercept(InstMethodsInterV2.java:76)
at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.exchange(ExchangeFunctions.java)
at org.springframework.web.reactive.function.client.DefaultWebClient$ObservationFilterFunction.filter(DefaultWebClient.java:747)
at org.springframework.web.reactive.function.client.ExchangeFilterFunction.lambda$andThen$0(ExchangeFilterFunction.java:62)
at reactor.core.publisher.MonoDefer.subscribe(MonoDefer.java:45)

[wu-sheng]

https://github.com/apache/skywalking-java/blob/67ab8b222fbb9a71b450665eb9f733380d813b8a/apm-sniffer/optional-plugins/optional-spring-plugins/optional-spring-cloud/gateway-4.x-plugin/pom.xml#L45

I think we only tested this in Gateway 4.x. I am not sure how it works in your end.

From reading the logs, Cannot invoke "org.apache.skywalking.apm.agent.core.context.ContextCarrier.items()" because "contextCarrier" is null means there is no exit span created before trying to do context injection.
Maybe(only maybe), this plugin only considers to run in gateway case, which there is span created before.

@CzyerChen If you are still watching here, please take a look.

[wh88725]

Thanks for your answer!
I recheck the stack and find that the webclient calling is excuted in a JDK thread pool, but I do not import the jdk-threadpool-plugin. So I think "no span created before" maybe the key point.

Next I will try two approaches to see what happens:

1. Use the Native API to start the trace context manually
2. Import and config the jdk-threadpool-plugin

Do you have any better suggestions?

[wu-sheng]

I don't have much to share. Yours should be a good start.

[eye-gu]

The same problem occurs when using JdkClientHttpConnector

[wu-sheng]

Your patch(apache/skywalking-java#834) has been accepted.