@SpanAttribute annotation with custom value resolver for an attribute

[ashwin-07]

Hello 👋

I was wondering if there was any value resolver kind of thing which is present for @SpanAttribute annotation for auto instrumentation. So that we could pass in something like @SpanAttribute(resolver=com.test.customAttrResolver.class) and the return value of the custom resolver would be recorded as value for the span attribute

Example:

Adding a sample code for illustration.

TestObject.java

public class TestObject {
    String field1;   //only this field should be recorded as value for the span attribute
    String field2;
    String field3;
}

Instrumented Method

@WithSpan("test method")
 private void processChange(@SpanAttribute TestObject testObject) {
    /*business logic*/
 }

I am looking for an option to record only the testObject.field1 property and leave out the rest two properties of the Span Attribute testObject as part of the span.

I guess overriding the toString method will help achieve this but I cannot override toString in my actual codebase because it is also used in other places as well. Is there any way to achieve this with SpanAttribute?

[mateuszrzeszutek]

Hey @ashwin-07 ,

Have you tried using Span.current() and just setting the value manually?

@WithSpan("test method")
private void processChange(TestObject testObject) {
    Span.current().setAttribute("my-custom-attr", testObject.field1);
    /*business logic*/
}

I believe it's a bit easier than implementing a custom resolver class (and takes less code).

[ashwin-07]

Yeah I am currently doing it that way, and it makes sense. But, We were previously using Sleuth and there was a custom extractor option for the equivalent SpanTag annotation. So was just curious to know if there is a way to do the same with the SpanAttribute

[mateuszrzeszutek]

So was just curious to know if there is a way to do the same with the SpanAttribute

No, there is not. In cases like this one, we usually recommend using Span.current().

[ashwin-07]

oh okay, thanks!

[trask]

(just fyi, there is one downside to using Span.current().setAttribute() which is that those attributes aren't available for attribute rule-based sampling, though this is generally a more advanced use-case)

[ashwin-07]

@trask I am using a custom sampler to filter out traces based on the span name, don't have a use case for sampling based on attributes. Thanks for pointing it out anyways