Class TextFormat

  • Direct Known Subclasses:
    B3Format, CloudTraceFormat, TextFormat.NoopTextFormat, TraceContextFormat

    @ExperimentalApi
    public abstract class TextFormat
    extends java.lang.Object
    Injects and extracts trace identifiers as text into carriers that travel in-band across process boundaries. Identifiers are often encoded as messaging or RPC request headers.

    When using http, the carrier of propagated data on both the client (injector) and server (extractor) side is usually an http request. Propagation is usually implemented via library- specific request interceptors, where the client-side injects span identifiers and the server-side extracts them.

    Example of usage on the client:

    
     private static final Tracer tracer = Tracing.getTracer();
     private static final TextFormat textFormat = Tracing.getPropagationComponent().getTextFormat();
     private static final TextFormat.Setter setter = new TextFormat.Setter<HttpURLConnection>() {
       public void put(HttpURLConnection carrier, String key, String value) {
         carrier.setRequestProperty(field, value);
       }
     }
    
     void makeHttpRequest() {
       Span span = tracer.spanBuilder("Sent.MyRequest").startSpan();
       try (Scope s = tracer.withSpan(span)) {
         HttpURLConnection connection =
             (HttpURLConnection) new URL("http://myserver").openConnection();
         textFormat.inject(span.getContext(), connection, httpURLConnectionSetter);
         // Send the request, wait for response and maybe set the status if not ok.
       }
       span.end();  // Can set a status.
     }
     

    Example of usage on the server:

    
     private static final Tracer tracer = Tracing.getTracer();
     private static final TextFormat textFormat = Tracing.getPropagationComponent().getTextFormat();
     private static final TextFormat.Getter<HttpRequest> getter = ...;
    
     void onRequestReceived(HttpRequest request) {
       SpanContext spanContext = textFormat.extract(request, getter);
       Span span = tracer.spanBuilderWithRemoteParent("Recv.MyRequest", spanContext).startSpan();
       try (Scope s = tracer.withSpan(span)) {
         // Handle request and send response back.
       }
       span.end()
     }
     
    Since:
    0.11
    • Constructor Detail

      • TextFormat

        public TextFormat()
    • Method Detail

      • fields

        public abstract java.util.List<java.lang.String> fields()
        The propagation fields defined. If your carrier is reused, you should delete the fields here before calling inject(SpanContext, Object, Setter).

        For example, if the carrier is a single-use or immutable request object, you don't need to clear fields as they couldn't have been set before. If it is a mutable, retryable object, successive calls should clear these fields first.

        Since:
        0.11
      • inject

        public abstract <C> void inject​(SpanContext spanContext,
                                        C carrier,
                                        TextFormat.Setter<C> setter)
        Injects the span context downstream. For example, as http headers.
        Parameters:
        spanContext - possibly not sampled.
        carrier - holds propagation fields. For example, an outgoing message or http request.
        setter - invoked for each propagation key to add or remove.
        Since:
        0.11
      • extract

        public abstract <C> SpanContext extract​(C carrier,
                                                TextFormat.Getter<C> getter)
                                         throws SpanContextParseException
        Extracts the span context from upstream. For example, as http headers.
        Parameters:
        carrier - holds propagation fields. For example, an outgoing message or http request.
        getter - invoked for each propagation key to get.
        Throws:
        SpanContextParseException - if the input is invalid
        Since:
        0.11
      • getNoopTextFormat

        static TextFormat getNoopTextFormat()
        Returns the no-op implementation of the TextFormat.
        Returns:
        the no-op implementation of the TextFormat.