Spring Gateway(2.x, 3.x, 4.x) Filter Enhancement in Java agent 9.4(release in 2025Q1)

[wu-sheng]

Summarized by @yqw570994511

This is a new thing started from #12839 and PR lands via apache/skywalking-java#736. It enhances the Spring Gateway plugins for GW 2.x, 3.x and 4.x with enhanced context.

Previously, we rely on Fetch APIs in Webflux Tracing Assistant APIs to obtain relative IDs and print out, but it provides inconsistent format in the logs. The official Trace ID/Context placeholder only prints N/A.

With the apache/skywalking-java#736 and released in 9.4, all filters that implement the GlobalFilter and GatewayFilter interfaces can output the logs automatically, meaning without manual codes requirement. And the trace/context IDs are injected into log placeholder.

• Demo codes use TraceContext.traceId(); and TraceContext.spanId();` for better readings, the log screenshot indicates the consistent outputs.

@Component
public class Filter1 implements GlobalFilter, Ordered {

    private static final Logger log = LoggerFactory.getLogger(Filter1.class);
    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        log.info("filter1 running");

        // fetch trace ID
        String traceId = TraceContext.traceId();
        log.info("filter1 traceId: {}", traceId);

        // fetch segment ID
        String segmentId = TraceContext.segmentId();
        log.info("filter1 segmentId: {}", segmentId);

        // fetch span ID
        int spanId = TraceContext.spanId();
        log.info("filter1 spanId: {}", spanId);

        return chain.filter(exchange);
    }
    @Override
    public int getOrder() {
        return -100;
    }
}

@Component
public class GatewayFilter1 implements GatewayFilter {

    private static final Logger log = LoggerFactory.getLogger(GatewayFilter1.class);
    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        log.info("gatewayFilter1 running");
        return chain.filter(exchange);
    }
}

The logs and manual APIs output are consistent

---

But there is still an exceptional case that users still need manual APIs, when they use chain.filter(exchange).then(...) as following

• Demo filter codes

@Component
public class Filter2 implements GlobalFilter, Ordered {

    private static final Logger log = LoggerFactory.getLogger(Filter2.class);
    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        log.info("filter2 running");

        // fetch trace ID
        String traceId = TraceContext.traceId();
        log.info("filter2 traceId: {}", traceId);

        // fetch segment ID
        String segmentId = TraceContext.segmentId();
        log.info("filter2 segmentId: {}", segmentId);

        // fetch span ID
        int spanId = TraceContext.spanId();
        log.info("filter2 spanId: {}", spanId);
        return chain.filter(exchange).then(Mono.fromRunnable(() -> {
            String traceId2 = WebFluxSkyWalkingTraceContext.traceId(exchange);
            log.info("filter2 then traceId: {}", traceId2);

            String segmentId2 = WebFluxSkyWalkingTraceContext.segmentId(exchange);
            log.info("filter2 then segmentId: {}", segmentId2);

            int spanId2 = WebFluxSkyWalkingTraceContext.spanId(exchange);
            log.info("filter2 then spanId: {}", spanId2);
        }));
    }

    @Override
    public int getOrder() {
        return 10;
    }
}

• Output logs without proper trace context, but manual APIs work well.