How to Access HttpServletRequest in Spring WebFlux Using Reactor Context

Explanation

In Spring Boot Web we can obtain the

HttpServletRequest

via

RequestContextHolder

. In Spring WebFlux this feature is missing, making it difficult to retrieve the request in AOP or other scenarios.

<code>ServletRequestAttributes requestAttributes = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();</code>
<code>// Get request</code>
<code>HttpServletRequest request = requestAttributes.getRequest();</code>

We first look for a solution in

spring-security

. The

ReactorContextWebFilter

shows how security stores the context.

<code>public class ReactorContextWebFilter implements WebFilter {
    private final ServerSecurityContextRepository repository;
    public ReactorContextWebFilter(ServerSecurityContextRepository repository) {
        Assert.notNull(repository, "repository cannot be null");
        this.repository = repository;
    }
    @Override
    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
        return chain.filter(exchange)
            .subscriberContext(c -> c.hasKey(SecurityContext.class) ? c : withSecurityContext(c, exchange));
    }
    private Context withSecurityContext(Context mainContext, ServerWebExchange exchange) {
        return mainContext.putAll(this.repository.load(exchange)
            .as(ReactiveSecurityContextHolder::withSecurityContext));
    }
}</code>

The filter uses

reactor.util.context.Context

, a ThreadLocal‑like feature introduced in Reactor 3.1.

Implementation in mica

The mica project provides a simple

ReactiveRequestContextFilter

that stores the

ServerHttpRequest

in the Reactor Context.

<code>@Configuration
@ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.REACTIVE)
public class ReactiveRequestContextFilter implements WebFilter {
    @Override
    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
        ServerHttpRequest request = exchange.getRequest();
        return chain.filter(exchange)
            .subscriberContext(ctx -> ctx.put(ReactiveRequestContextHolder.CONTEXT_KEY, request));
    }
}</code>

The helper

ReactiveRequestContextHolder

retrieves the request from the Context.

<code>public class ReactiveRequestContextHolder {
    static final Class<ServerHttpRequest> CONTEXT_KEY = ServerHttpRequest.class;
    public static Mono<ServerHttpRequest> getRequest() {
        return Mono.subscriberContext()
            .map(ctx -> ctx.get(CONTEXT_KEY));
    }
}</code>

How to Use It

Exception handling with the stored request

<code>@ExceptionHandler(Throwable.class)
@ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
public Mono<?> handleError(Throwable e) {
    log.error("未知异常", e);
    return ReactiveRequestContextHolder.getRequest()
        .doOnSuccess(r -> publishEvent(r, e))
        .flatMap(r -> Mono.just(R.fail(SystemCode.FAILURE)));
}
private void publishEvent(ServerHttpRequest request, Throwable error) {
    // business logic
}</code>

WebClient header propagation

<code>@GetMapping("/test")
@ResponseBody
public Mono<String> test() {
    WebClient webClient = testClient();
    return webClient.get().uri("").retrieve().bodyToMono(String.class);
}
@Bean
public WebClient testClient() {
    return WebClient.builder()
        .filter(testFilterFunction())
        .baseUrl("https://www.baidu.com")
        .build();
}
private ExchangeFilterFunction testFilterFunction() {
    return (request, next) -> ReactiveRequestContextHolder.getRequest()
        .flatMap(r -> {
            ClientRequest clientRequest = ClientRequest.from(request)
                .headers(headers -> headers.set(HttpHeaders.USER_AGENT,
                    r.getHeaders().getFirst(HttpHeaders.USER_AGENT)))
                .build();
            return next.exchange(clientRequest);
        });
}</code>

These examples demonstrate how to retrieve the original request for logging, error handling, and forwarding headers when using Spring WebFlux.

References

[1]

: https://github.com/spring-projects/spring-security/blob/master/web/src/main/java/org/springframework/security/web/server/context/ReactorContextWebFilter.java#L43

[2]

: https://projectreactor.io/docs/core/release/reference/#context

[3]

: https://www.oschina.net/question/2315449_2305069