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Write TraceId in HTTP Response headers
Prior to this commit, the Micrometer instrumentation support would auto-configure a `ServerHttpObservationFilter` for creating observations in Spring MVC applications. As of Spring Framework 6.2, applications can extend this filter class to get notified of the observation scope being opened. This commit contributes a new `TraceHeaderObservationFilter` implementation that writes the current Trace Id (if present) to the `X-Trace-Id` HTTP response header. This feature is disabled by default, applications will need to enable `management.observations.http.server.requests.write-trace-header`. ` Closes gh-40857
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8 files changed

+323
-27
lines changed

8 files changed

+323
-27
lines changed

‎spring-boot-project/spring-boot-actuator-autoconfigure/build.gradle‎

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@@ -136,6 +136,7 @@ dependencies {
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testImplementation(project(":spring-boot-project:spring-boot-test"))
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testImplementation(project(":spring-boot-project:spring-boot-tools:spring-boot-test-support"))
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testImplementation("io.micrometer:micrometer-observation-test")
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testImplementation("io.micrometer:micrometer-tracing-test")
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testImplementation("io.projectreactor:reactor-test")
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testImplementation("io.prometheus:prometheus-metrics-exposition-formats")
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testImplementation("io.r2dbc:r2dbc-h2")

‎spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/observation/ObservationProperties.java‎

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@@ -1,5 +1,5 @@
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/*
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* Copyright 2012-2024 the original author or authors.
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* Copyright 2012-2025 the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
@@ -127,6 +127,11 @@ public static class ServerRequests {
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*/
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private String name = "http.server.requests";
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/**
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* Whether to write the "X-Trace-Id" HTTP response header.
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*/
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private boolean writeTraceHeader = false;
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public String getName() {
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return this.name;
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}
@@ -135,6 +140,14 @@ public void setName(String name) {
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this.name = name;
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}
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public boolean isWriteTraceHeader() {
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return this.writeTraceHeader;
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}
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public void setWriteTraceHeader(boolean writeTraceHeader) {
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this.writeTraceHeader = writeTraceHeader;
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}
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}
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}

‎spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/observation/web/servlet/ObservationFilterConfigurations.java‎

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/*
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* Copyright 2012-2025 the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* https://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.springframework.boot.actuate.autoconfigure.observation.web.servlet;
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import io.micrometer.observation.ObservationRegistry;
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import io.micrometer.tracing.Tracer;
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import jakarta.servlet.DispatcherType;
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import org.springframework.beans.factory.ObjectProvider;
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import org.springframework.boot.actuate.autoconfigure.observation.ObservationProperties;
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import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
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import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
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import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
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import org.springframework.boot.autoconfigure.web.servlet.ConditionalOnMissingFilterBean;
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import org.springframework.boot.web.servlet.FilterRegistrationBean;
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import org.springframework.context.annotation.Bean;
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import org.springframework.context.annotation.Configuration;
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import org.springframework.core.Ordered;
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import org.springframework.http.server.observation.DefaultServerRequestObservationConvention;
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import org.springframework.http.server.observation.ServerRequestObservationConvention;
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import org.springframework.web.filter.ServerHttpObservationFilter;
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/**
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* Observation filter configurations imported by
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* {@link WebMvcObservationAutoConfiguration}.
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*
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* @author Brian Clozel
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*/
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abstract class ObservationFilterConfigurations {
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static <T extends ServerHttpObservationFilter> FilterRegistrationBean<T> filterRegistration(T filter) {
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FilterRegistrationBean<T> registration = new FilterRegistrationBean<>(filter);
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registration.setOrder(Ordered.HIGHEST_PRECEDENCE + 1);
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registration.setDispatcherTypes(DispatcherType.REQUEST, DispatcherType.ASYNC);
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return registration;
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}
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@Configuration(proxyBeanMethods = false)
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@ConditionalOnClass(Tracer.class)
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static class TracingHeaderObservation {
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@Bean
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@ConditionalOnProperty(prefix = "management.observations.http.server.requests", name = "write-trace-header")
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@ConditionalOnBean(Tracer.class)
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@ConditionalOnMissingFilterBean({ ServerHttpObservationFilter.class, TraceHeaderObservationFilter.class })
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FilterRegistrationBean<TraceHeaderObservationFilter> webMvcObservationFilter(ObservationRegistry registry,
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Tracer tracer, ObjectProvider<ServerRequestObservationConvention> customConvention,
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ObservationProperties observationProperties) {
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String name = observationProperties.getHttp().getServer().getRequests().getName();
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ServerRequestObservationConvention convention = customConvention
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.getIfAvailable(() -> new DefaultServerRequestObservationConvention(name));
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TraceHeaderObservationFilter filter = new TraceHeaderObservationFilter(tracer, registry, convention);
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return filterRegistration(filter);
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}
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}
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@Configuration(proxyBeanMethods = false)
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static class DefaultObservation {
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@Bean
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@ConditionalOnMissingFilterBean({ ServerHttpObservationFilter.class, TraceHeaderObservationFilter.class })
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FilterRegistrationBean<ServerHttpObservationFilter> webMvcObservationFilter(ObservationRegistry registry,
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ObjectProvider<ServerRequestObservationConvention> customConvention,
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ObservationProperties observationProperties) {
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String name = observationProperties.getHttp().getServer().getRequests().getName();
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ServerRequestObservationConvention convention = customConvention
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.getIfAvailable(() -> new DefaultServerRequestObservationConvention(name));
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ServerHttpObservationFilter filter = new ServerHttpObservationFilter(registry, convention);
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return filterRegistration(filter);
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}
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}
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}

‎spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/observation/web/servlet/TraceHeaderObservationFilter.java‎

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/*
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* Copyright 2012-2025 the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* https://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.springframework.boot.actuate.autoconfigure.observation.web.servlet;
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import io.micrometer.observation.Observation.Scope;
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import io.micrometer.observation.ObservationRegistry;
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import io.micrometer.tracing.Span;
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import io.micrometer.tracing.Tracer;
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import jakarta.servlet.http.HttpServletRequest;
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import jakarta.servlet.http.HttpServletResponse;
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import org.springframework.http.server.observation.ServerRequestObservationConvention;
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import org.springframework.util.Assert;
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import org.springframework.web.filter.ServerHttpObservationFilter;
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/**
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* {@link ServerHttpObservationFilter} that writes the current {@link Span} in an HTTP
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* response header. By default, the {@code "X-Trace-Id"} header is used.
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*
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* @author Brian Clozel
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* @since 3.5.0
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*/
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public class TraceHeaderObservationFilter extends ServerHttpObservationFilter {
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private static final String TRACE_ID_HEADER_NAME = "X-Trace-Id";
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private final Tracer tracer;
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/**
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* Create a {@link TraceHeaderObservationFilter} that will write the
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* {@code "X-Trace-Id"} HTTP response header.
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* @param tracer the current tracer
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* @param observationRegistry the current observation registry
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*/
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public TraceHeaderObservationFilter(Tracer tracer, ObservationRegistry observationRegistry) {
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super(observationRegistry);
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Assert.notNull(tracer, "Tracer must not be null");
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this.tracer = tracer;
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}
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/**
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* Create a {@link TraceHeaderObservationFilter} that will write the
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* {@code "X-Trace-Id"} HTTP response header.
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* @param tracer the current tracer
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* @param observationRegistry the current observation registry
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* @param observationConvention the custom observation convention to use.
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*/
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public TraceHeaderObservationFilter(Tracer tracer, ObservationRegistry observationRegistry,
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ServerRequestObservationConvention observationConvention) {
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super(observationRegistry, observationConvention);
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Assert.notNull(tracer, "Tracer must not be null");
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this.tracer = tracer;
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}
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@Override
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protected void onScopeOpened(Scope scope, HttpServletRequest request, HttpServletResponse response) {
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Span currentSpan = this.tracer.currentSpan();
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if (currentSpan != null && !currentSpan.isNoop()) {
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response.setHeader(TRACE_ID_HEADER_NAME, currentSpan.context().traceId());
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}
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}
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}

‎spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/observation/web/servlet/WebMvcObservationAutoConfiguration.java‎

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/*
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* Copyright 2012-2023 the original author or authors.
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* Copyright 2012-2025 the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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import io.micrometer.core.instrument.config.MeterFilter;
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import io.micrometer.observation.Observation;
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import io.micrometer.observation.ObservationRegistry;
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import jakarta.servlet.DispatcherType;
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import org.springframework.beans.factory.ObjectProvider;
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import org.springframework.boot.actuate.autoconfigure.metrics.CompositeMeterRegistryAutoConfiguration;
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import org.springframework.boot.actuate.autoconfigure.metrics.MetricsAutoConfiguration;
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import org.springframework.boot.actuate.autoconfigure.metrics.MetricsProperties;
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import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
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import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
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import org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication;
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import org.springframework.boot.autoconfigure.web.servlet.ConditionalOnMissingFilterBean;
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import org.springframework.boot.context.properties.EnableConfigurationProperties;
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import org.springframework.boot.web.servlet.FilterRegistrationBean;
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import org.springframework.context.annotation.Bean;
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import org.springframework.context.annotation.Configuration;
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import org.springframework.core.Ordered;
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import org.springframework.context.annotation.Import;
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import org.springframework.core.annotation.Order;
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import org.springframework.http.server.observation.DefaultServerRequestObservationConvention;
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import org.springframework.http.server.observation.ServerRequestObservationConvention;
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import org.springframework.web.filter.ServerHttpObservationFilter;
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import org.springframework.web.servlet.DispatcherServlet;
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/**
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@ConditionalOnClass({ DispatcherServlet.class, Observation.class })
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@ConditionalOnBean(ObservationRegistry.class)
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@EnableConfigurationProperties({ MetricsProperties.class, ObservationProperties.class })
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@Import({ ObservationFilterConfigurations.TracingHeaderObservation.class,
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ObservationFilterConfigurations.DefaultObservation.class })
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public class WebMvcObservationAutoConfiguration {
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@Bean
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@ConditionalOnMissingFilterBean
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public FilterRegistrationBean<ServerHttpObservationFilter> webMvcObservationFilter(ObservationRegistry registry,
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ObjectProvider<ServerRequestObservationConvention> customConvention,
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ObservationProperties observationProperties) {
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String name = observationProperties.getHttp().getServer().getRequests().getName();
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ServerRequestObservationConvention convention = customConvention
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.getIfAvailable(() -> new DefaultServerRequestObservationConvention(name));
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ServerHttpObservationFilter filter = new ServerHttpObservationFilter(registry, convention);
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FilterRegistrationBean<ServerHttpObservationFilter> registration = new FilterRegistrationBean<>(filter);
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registration.setOrder(Ordered.HIGHEST_PRECEDENCE + 1);
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registration.setDispatcherTypes(DispatcherType.REQUEST, DispatcherType.ASYNC);
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return registration;
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}
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@Configuration(proxyBeanMethods = false)
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@ConditionalOnClass(MeterRegistry.class)
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@ConditionalOnBean(MeterRegistry.class)

‎spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/observation/web/servlet/TraceHeaderObservationFilterTests.java‎

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/*
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* Copyright 2012-2025 the original author or authors.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* https://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package org.springframework.boot.actuate.autoconfigure.observation.web.servlet;
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import io.micrometer.observation.tck.TestObservationRegistry;
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import io.micrometer.tracing.Tracer;
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import io.micrometer.tracing.handler.DefaultTracingObservationHandler;
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import io.micrometer.tracing.test.simple.SimpleTracer;
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import jakarta.servlet.FilterChain;
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import org.junit.jupiter.api.Test;
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import org.springframework.mock.web.MockHttpServletRequest;
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import org.springframework.mock.web.MockHttpServletResponse;
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import static org.assertj.core.api.Assertions.assertThat;
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/**
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* Tests for {@link TraceHeaderObservationFilter}.
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*/
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class TraceHeaderObservationFilterTests {
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TestObservationRegistry observationRegistry = TestObservationRegistry.create();
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@Test
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void shouldWriteTraceHeaderWhenCurrentTrace() throws Exception {
40+
TraceHeaderObservationFilter filter = createFilter(new SimpleTracer());
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MockHttpServletResponse response = new MockHttpServletResponse();
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filter.doFilter(new MockHttpServletRequest(), response, getFilterChain());
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assertThat(response.getHeader("X-Trace-Id")).isNotEmpty();
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}
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@Test
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void shouldNotWriteTraceHeaderWhenNoCurrentTrace() throws Exception {
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TraceHeaderObservationFilter filter = createFilter(Tracer.NOOP);
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MockHttpServletResponse response = new MockHttpServletResponse();
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filter.doFilter(new MockHttpServletRequest(), response, getFilterChain());
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assertThat(response.getHeaderNames()).doesNotContain("X-Trace-Id");
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}
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private TraceHeaderObservationFilter createFilter(Tracer tracer) {
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this.observationRegistry.observationConfig().observationHandler(new DefaultTracingObservationHandler(tracer));
59+
return new TraceHeaderObservationFilter(tracer, this.observationRegistry);
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}
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private static FilterChain getFilterChain() {
63+
return (servletRequest, servletResponse) -> servletResponse.getWriter().print("Hello");
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}
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}

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