How can I control a trace so that only the root span is called?

[zerocooldog]

Looking into the OTEL instrumentation module, I found that there are advice classes related to servlets.

https://github.com/open-telemetry/opentelemetry-java-instrumentation/tree/main/instrumentation/servlet

And by registering a CustomSpanProcessor, I get that the context object in the onStart method of the SpanProcessor logs information such as HttpRouteState or opentelemetry-servlet-app-server-bridge.

-CustomSpanProcc

public class Hamonica2SpanProcessor implements SpanProcessor {
    private final Logger log = Logger.getLogger(getClass().getName());
    private static final ContextKey<HttpRouteState> KEY =
            ContextKey.named("opentelemetry-http-server-route-key");
    @Override
    public void onStart(Context context, ReadWriteSpan readWriteSpan) {

        HttpRouteState httpRouteState = context.get(KEY);
        log.log(Level.SEVERE,"###### start context : {0}", new Object[]{context});
        log.log(Level.SEVERE,"###### start httpRouteState  : {0}", new Object[]{httpRouteState});
    }

...
...
}

• context Object toString

 {opentelemetry-http-server-route-key=io.opentelemetry.javaagent.shaded.instrumentation.api.internal.HttpRouteState@2e184ef5, opentelemetry-servlet-app-server-bridge=io.opentelemetry.javaagent.bootstrap.servlet.AppServerBridge@20dfb546}

Here are my questions:

1. I'm trying to access the HttpRouteState value from the context within a SpanProcessor, but it's always null. Am I using the context.get(KEY) method correctly? When I log the entire context object, it seems to contain the desired information.

2. I'm trying to optimize my tracing configuration. Can I initiate and terminate the root span just once, regardless of the number of child spans within a trace? I aim to reduce overhead and improve performance.

[laurit]

1. Context keys use identity comparison, you must use the exact same key instance that was used to set the value. Also route is often set after span is created so it will not be available in the onStart method.
2. I don't understand the question.