“How-to” Guides

import org.springframework.context.annotation.Configuration;
import org.springframework.web.client.RestTemplate;

@Configuration(proxyBeanMethods = false)
class MyConfiguration {
    @Bean RestTemplate myRestTemplate() {
        return new RestTemplate();
    }
}

@Service
class MyService {
    private final RestTemplate restTemplate;

    MyService(RestTemplate restTemplate) {
        this.restTemplate = restTemplate;
    }

    String makeACall() {
        return this.restTemplate.getForObject("http://example.com", String.class);
    }

}

@Service
class MyService {

    String makeACall() {
        // This will not work because RestTemplate is not a bean
        return new RestTemplate().getForObject("http://example.com", String.class);
    }

}

import org.springframework.cloud.sleuth.Span;
import org.springframework.cloud.sleuth.Tracer;

import javax.servlet.Filter;
import org.springframework.web.server.WebFilter;

@Configuration(proxyBeanMethods = false)
class MyConfig {

        // Example of a servlet Filter for non-reactive applications
        @Bean
        Filter traceIdInResponseFilter(Tracer tracer) {
            return (request, response, chain) -> {
                Span currentSpan = tracer.currentSpan();
                if (currentSpan != null) {
                    HttpServletResponse resp = (HttpServletResponse) response;
                    // putting trace id value in [mytraceid] response header
                    resp.addHeader("mytraceid", currentSpan.context().traceId());
                }
                chain.doFilter(request, response);
            };
        }

        // Example of a reactive WebFilter for reactive applications
        @Bean
        WebFilter traceIdInResponseFilter(Tracer tracer) {
            return (exchange, chain) -> {
                Span currentSpan = tracer.currentSpan();
                if (currentSpan != null) {
                    // putting trace id value in [mytraceid] response header
                    exchange.getResponse().getHeaders().add("mytraceid", currentSpan.context().traceId());
                }
                return chain.filter(exchange);
            };
        }
}

@Configuration(proxyBeanMethods = false)
public static class ClientParserConfiguration {

    // example for Feign
    @Bean(name = HttpClientRequestParser.NAME)
    HttpRequestParser myHttpClientRequestParser() {
        return (request, context, span) -> {
            // Span customization
            span.name(request.method());
            span.tag("ClientRequest", "Tag");
            Object unwrap = request.unwrap();
            if (unwrap instanceof feign.Request) {
                feign.Request req = (feign.Request) unwrap;
                // Span customization
                span.tag("ClientRequestFeign", req.httpMethod().name());
            }
        };
    }

    // example for Feign
    @Bean(name = HttpClientResponseParser.NAME)
    HttpResponseParser myHttpClientResponseParser() {
        return (response, context, span) -> {
            // Span customization
            span.tag("ClientResponse", "Tag");
            Object unwrap = response.unwrap();
            if (unwrap instanceof feign.Response) {
                feign.Response resp = (feign.Response) unwrap;
                // Span customization
                span.tag("ClientResponseFeign", String.valueOf(resp.status()));
            }
        };
    }

}

@Configuration(proxyBeanMethods = false)
public static class ServerParserConfiguration {

    @Bean(name = HttpServerRequestParser.NAME)
    HttpRequestParser myHttpRequestParser() {
        return (request, context, span) -> {
            // Span customization
            span.tag("ServerRequest", "Tag");
            Object unwrap = request.unwrap();
            if (unwrap instanceof HttpServletRequest) {
                HttpServletRequest req = (HttpServletRequest) unwrap;
                // Span customization
                span.tag("ServerRequestServlet", req.getMethod());
            }
        };
    }

    @Bean(name = HttpServerResponseParser.NAME)
    HttpResponseParser myHttpResponseParser() {
        return (response, context, span) -> {
            // Span customization
            span.tag("ServerResponse", "Tag");
            Object unwrap = response.unwrap();
            if (unwrap instanceof HttpServletResponse) {
                HttpServletResponse resp = (HttpServletResponse) unwrap;
                // Span customization
                span.tag("ServerResponseServlet", String.valueOf(resp.getStatus()));
            }
        };
    }

    @Bean
    Filter traceIdInResponseFilter(Tracer tracer) {
        return (request, response, chain) -> {
            Span currentSpan = tracer.currentSpan();
            if (currentSpan != null) {
                HttpServletResponse resp = (HttpServletResponse) response;
                resp.addHeader("mytraceid", currentSpan.context().traceId());
            }
            chain.doFilter(request, response);
        };
    }

}

@Component
class CustomPropagator extends Propagation.Factory implements Propagation<String> {

    @Override
    public List<String> keys() {
        return Arrays.asList("myCustomTraceId", "myCustomSpanId");
    }

    @Override
    public <R> TraceContext.Injector<R> injector(Setter<R, String> setter) {
        return (traceContext, request) -> {
            setter.put(request, "myCustomTraceId", traceContext.traceIdString());
            setter.put(request, "myCustomSpanId", traceContext.spanIdString());
        };
    }

    @Override
    public <R> TraceContext.Extractor<R> extractor(Getter<R, String> getter) {
        return request -> TraceContextOrSamplingFlags.create(TraceContext.newBuilder()
                .traceId(HexCodec.lowerHexToUnsignedLong(getter.get(request, "myCustomTraceId")))
                .spanId(HexCodec.lowerHexToUnsignedLong(getter.get(request, "myCustomSpanId"))).build());
    }

    @Override
    public <K> Propagation<K> create(KeyFactory<K> keyFactory) {
        return StringPropagationAdapter.create(this, keyFactory);
    }

}