Make SpanContextHolder package private

That way it can't leak back out into public classes, particularly
in intrumentation. Such use cases should use TraceAccessor or
Tracer exclusively.

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/autoconfig/TraceAutoConfiguration.java

@@ -31,7 +31,7 @@ import org.springframework.cloud.sleuth.metric.CounterServiceBasedSpanReporterSe
 import org.springframework.cloud.sleuth.metric.NoOpSpanReporterService;
 import org.springframework.cloud.sleuth.metric.SleuthMetricProperties;
 import org.springframework.cloud.sleuth.metric.SpanReporterService;
-import org.springframework.cloud.sleuth.sampler.IsTracingSampler;
+import org.springframework.cloud.sleuth.sampler.NeverSampler;
 import org.springframework.cloud.sleuth.trace.DefaultTracer;
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.context.annotation.Bean;
@@ -54,7 +54,7 @@ public class TraceAutoConfiguration {
 	@Bean
 	@ConditionalOnMissingBean
 	public Sampler defaultTraceSampler() {
-		return new IsTracingSampler();
+		return NeverSampler.INSTANCE;
 	}
 
 	@Bean

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/integration/TraceChannelInterceptor.java

@@ -21,7 +21,7 @@ import java.util.Random;
 import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.Tracer;
 import org.springframework.cloud.sleuth.instrument.TraceKeys;
-import org.springframework.cloud.sleuth.sampler.IsTracingSampler;
+import org.springframework.cloud.sleuth.sampler.NeverSampler;
 import org.springframework.messaging.Message;
 import org.springframework.messaging.MessageChannel;
 
@@ -54,7 +54,7 @@ public class TraceChannelInterceptor extends AbstractTraceChannelInterceptor {
 			return getTracer().joinTrace(name, span);
 		}
 		if (message.getHeaders().containsKey(Span.NOT_SAMPLED_NAME)) {
-			return getTracer().startTrace(name, IsTracingSampler.INSTANCE);
+			return getTracer().startTrace(name, NeverSampler.INSTANCE);
 		}
 		return getTracer().startTrace(name);
 	}

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/instrument/web/TraceFilter.java

@@ -35,7 +35,7 @@ import org.springframework.cloud.sleuth.Tracer;
 import org.springframework.cloud.sleuth.event.ServerReceivedEvent;
 import org.springframework.cloud.sleuth.event.ServerSentEvent;
 import org.springframework.cloud.sleuth.instrument.TraceKeys;
-import org.springframework.cloud.sleuth.sampler.IsTracingSampler;
+import org.springframework.cloud.sleuth.sampler.NeverSampler;
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.context.ApplicationEventPublisherAware;
@@ -156,7 +156,7 @@ public class TraceFilter extends OncePerRequestFilter
 			else {
 				if (skip) {
 					spanFromRequest = this.tracer.startTrace(name,
-							IsTracingSampler.INSTANCE);
+							NeverSampler.INSTANCE);
 				}
 				else {
 					spanFromRequest = this.tracer.startTrace(name);

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/sampler/IsTracingSampler.java

@@ -18,17 +18,22 @@ package org.springframework.cloud.sleuth.sampler;
 
 import org.springframework.cloud.sleuth.Sampler;
 import org.springframework.cloud.sleuth.Span;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.SpanAccessor;
 
 /**
  * @author Spencer Gibb
  */
 public class IsTracingSampler implements Sampler {
 
-	public static IsTracingSampler INSTANCE = new IsTracingSampler();
+	private SpanAccessor accessor;
+
+	public IsTracingSampler(SpanAccessor accessor) {
+		super();
+		this.accessor = accessor;
+	}
 
 	@Override
 	public boolean isSampled(Span span) {
-		return SpanContextHolder.isTracing();
+		return this.accessor.isTracing();
 	}
 }

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/sampler/NeverSampler.java

@@ -0,0 +1,33 @@
+/*
+ * Copyright 2013-2015 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.sleuth.sampler;
+
+import org.springframework.cloud.sleuth.Sampler;
+import org.springframework.cloud.sleuth.Span;
+
+/**
+ * @author Spencer Gibb
+ */
+public class NeverSampler implements Sampler {
+
+	public static NeverSampler INSTANCE = new NeverSampler();
+
+	@Override
+	public boolean isSampled(Span span) {
+		return false;
+	}
+}

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/trace/SpanContextHolder.java

@@ -22,35 +22,47 @@ import org.springframework.core.NamedThreadLocal;
 import lombok.extern.apachecommons.CommonsLog;
 
 /**
+ * Utility for managing the thread local state for the {@link DefaultTracer}.
+ *
  * @author Spencer Gibb
+ * @author Dave Syer
  */
 @CommonsLog
-public class SpanContextHolder {
+class SpanContextHolder {
 
 	private static final ThreadLocal<SpanContext> CURRENT_SPAN = new NamedThreadLocal<>(
 			"Trace Context");
 
-	public static Span getCurrentSpan() {
+	/**
+	 * Get the current span out of the thread context
+	 */
+	static Span getCurrentSpan() {
 		return isTracing() ? CURRENT_SPAN.get().span : null;
 	}
 
-	public static void setCurrentSpan(Span span) {
-		// backwards compatibility
-		if (span == null) {
-			CURRENT_SPAN.remove();
-			return;
-		}
+	/**
+	 * Set the current span in the thread context
+	 */
+	static void setCurrentSpan(Span span) {
 		if (log.isTraceEnabled()) {
 			log.trace("Setting current span " + span);
 		}
 		push(span, false);
 	}
 
-	public static void removeCurrentSpan() {
+	/**
+	 * Remove all thread context relating to spans (useful for testing).
+	 *
+	 * @see #close() for a better alternative in instrumetation
+	 */
+	static void removeCurrentSpan() {
 		CURRENT_SPAN.remove();
 	}
 
-	public static boolean isTracing() {
+	/**
+	 * Check if there is already a span in the current thread
+	 */
+	static boolean isTracing() {
 		return CURRENT_SPAN.get() != null;
 	}
 
@@ -71,6 +83,11 @@ public class SpanContextHolder {
 		}
 	}
 
+	/**
+	 * Push a span into the thread context, with the option to have it auto close if any
+	 * child spans are themselves closed. Use autoClose=true if you start a new span with
+	 * a parent that wasn't already in thread context.
+	 */
 	static void push(Span span, boolean autoClose) {
 		if (isCurrent(span)) {
 			return;

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/TraceCallableTests.java

@@ -9,7 +9,7 @@ import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.Tracer;
 import org.springframework.cloud.sleuth.sampler.AlwaysSampler;
 import org.springframework.cloud.sleuth.trace.DefaultTracer;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.ApplicationEventPublisher;
 
 import java.util.Random;
@@ -28,7 +28,7 @@ public class TraceCallableTests {
 
 	@After
 	public void clean() {
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@Test
@@ -78,7 +78,7 @@ public class TraceCallableTests {
 		return new Callable<Span>() {
 			@Override
 			public Span call() throws Exception {
-				return SpanContextHolder.getCurrentSpan();
+				return TestSpanContextHolder.getCurrentSpan();
 			}
 		};
 	}

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/TraceRunnableTests.java

@@ -9,7 +9,7 @@ import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.Tracer;
 import org.springframework.cloud.sleuth.sampler.AlwaysSampler;
 import org.springframework.cloud.sleuth.trace.DefaultTracer;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.ApplicationEventPublisher;
 
 import java.util.Random;
@@ -27,7 +27,7 @@ public class TraceRunnableTests {
 
 	@After
 	public void cleanup() {
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@Test
@@ -91,7 +91,7 @@ public class TraceRunnableTests {
 
 		@Override
 		public void run() {
-			this.span = SpanContextHolder.getCurrentSpan();
+			this.span = TestSpanContextHolder.getCurrentSpan();
 		}
 	}
 

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/executor/TraceableExecutorServiceTests.java

@@ -11,7 +11,7 @@ import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.Tracer;
 import org.springframework.cloud.sleuth.sampler.AlwaysSampler;
 import org.springframework.cloud.sleuth.trace.DefaultTracer;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.ApplicationEventPublisher;
 
 import java.util.ArrayList;
@@ -40,7 +40,7 @@ public class TraceableExecutorServiceTests {
 	public void setup() {
 		this.tracer = new DefaultTracer(new AlwaysSampler(), new Random(), this.publisher);
 		this.traceManagerableExecutorService = new TraceableExecutorService(this.executorService, this.tracer);
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@After
@@ -48,7 +48,7 @@ public class TraceableExecutorServiceTests {
 		this.tracer = null;
 		this.traceManagerableExecutorService.shutdown();
 		this.executorService.shutdown();
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@Test
@@ -77,7 +77,7 @@ public class TraceableExecutorServiceTests {
 
 		@Override
 		public void run() {
-			Span span = SpanContextHolder.getCurrentSpan();
+			Span span = TestSpanContextHolder.getCurrentSpan();
 			this.traceIds.add(span.getTraceId());
 			this.spanIds.add(span.getSpanId());
 		}

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/hystrix/HystrixAnnotationsIntegrationTests.java

@@ -14,7 +14,7 @@ import org.springframework.cloud.netflix.hystrix.EnableHystrix;
 import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.Tracer;
 import org.springframework.cloud.sleuth.instrument.DefaultTestAutoConfiguration;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.test.annotation.DirtiesContext;
@@ -36,7 +36,7 @@ public class HystrixAnnotationsIntegrationTests {
 
 	@After
 	public void cleanTrace() {
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@Test
@@ -92,7 +92,7 @@ public class HystrixAnnotationsIntegrationTests {
 		@HystrixCommand
 		public void invokeLogicWrappedInHystrixCommand() {
 			this.spanCaughtFromHystrixThread = new AtomicReference<>(
-					SpanContextHolder.getCurrentSpan());
+					TestSpanContextHolder.getCurrentSpan());
 		}
 
 		public Long getTraceId() {

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/hystrix/TraceCommandTests.java

@@ -14,7 +14,7 @@ import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.Tracer;
 import org.springframework.cloud.sleuth.sampler.AlwaysSampler;
 import org.springframework.cloud.sleuth.trace.DefaultTracer;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.ApplicationEventPublisher;
 
 import com.netflix.hystrix.HystrixCommandProperties;
@@ -28,12 +28,12 @@ public class TraceCommandTests {
 
 	@Before
 	public void setup() {
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@After
 	public void cleanup() {
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@Test
@@ -74,7 +74,7 @@ public class TraceCommandTests {
 						.withExecutionTimeoutEnabled(false))) {
 			@Override
 			public Span doRun() throws Exception {
-				return SpanContextHolder.getCurrentSpan();
+				return TestSpanContextHolder.getCurrentSpan();
 			}
 		};
 	}

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/integration/TraceChannelInterceptorTests.java

@@ -39,7 +39,7 @@ import org.springframework.cloud.sleuth.Tracer;
 import org.springframework.cloud.sleuth.event.SpanReleasedEvent;
 import org.springframework.cloud.sleuth.instrument.integration.TraceChannelInterceptorTests.App;
 import org.springframework.cloud.sleuth.sampler.AlwaysSampler;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.event.EventListener;
@@ -81,7 +81,7 @@ public class TraceChannelInterceptorTests implements MessageHandler {
 	@Override
 	public void handleMessage(Message<?> message) throws MessagingException {
 		this.message = message;
-		this.span = SpanContextHolder.getCurrentSpan();
+		this.span = TestSpanContextHolder.getCurrentSpan();
 	}
 
 	@Before
@@ -91,7 +91,7 @@ public class TraceChannelInterceptorTests implements MessageHandler {
 
 	@After
 	public void close() {
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 		this.channel.unsubscribe(this);
 	}
 
@@ -103,7 +103,7 @@ public class TraceChannelInterceptorTests implements MessageHandler {
 
 		String spanId = this.message.getHeaders().get(Span.SPAN_ID_NAME, String.class);
 		assertNotNull("spanId was null", spanId);
-		assertNull(SpanContextHolder.getCurrentSpan());
+		assertNull(TestSpanContextHolder.getCurrentSpan());
 		assertFalse(this.span.isExportable());
 	}
 
@@ -133,7 +133,7 @@ public class TraceChannelInterceptorTests implements MessageHandler {
 
 		String traceId = this.message.getHeaders().get(Span.TRACE_ID_NAME, String.class);
 		assertNotNull("traceId was null", traceId);
-		assertNull(SpanContextHolder.getCurrentSpan());
+		assertNull(TestSpanContextHolder.getCurrentSpan());
 	}
 
 	@Test
@@ -148,7 +148,7 @@ public class TraceChannelInterceptorTests implements MessageHandler {
 
 		String traceId = this.message.getHeaders().get(Span.TRACE_ID_NAME, String.class);
 		assertNotNull("traceId was null", traceId);
-		assertNull(SpanContextHolder.getCurrentSpan());
+		assertNull(TestSpanContextHolder.getCurrentSpan());
 	}
 
 	// TODO: Refactor to parametrized test together with sending messages via channel
@@ -164,7 +164,7 @@ public class TraceChannelInterceptorTests implements MessageHandler {
 
 		String traceId = this.message.getHeaders().get(Span.TRACE_ID_NAME, String.class);
 		assertNotNull("traceId was null", traceId);
-		assertNull(SpanContextHolder.getCurrentSpan());
+		assertNull(TestSpanContextHolder.getCurrentSpan());
 	}
 
 	@Configuration

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/integration/TraceContextPropagationChannelInterceptorTests.java

@@ -28,7 +28,7 @@ import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.Tracer;
 import org.springframework.cloud.sleuth.instrument.integration.TraceContextPropagationChannelInterceptorTests.App;
 import org.springframework.cloud.sleuth.sampler.AlwaysSampler;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.integration.channel.QueueChannel;
@@ -59,7 +59,7 @@ public class TraceContextPropagationChannelInterceptorTests {
 
 	@After
 	public void close() {
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@Test

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/scheduling/TracingOnScheduledTests.java

@@ -9,7 +9,7 @@ import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.test.SpringApplicationConfiguration;
 import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.instrument.DefaultTestAutoConfiguration;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.scheduling.annotation.Scheduled;
@@ -70,7 +70,7 @@ class TestBeanWithScheduledMethod {
 
 	@Scheduled(fixedDelay = 1L)
 	public void scheduledMethod() {
-		this.span = SpanContextHolder.getCurrentSpan();
+		this.span = TestSpanContextHolder.getCurrentSpan();
 	}
 
 	public Span getSpan() {

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/web/TraceAsyncIntegrationTests.java

@@ -10,7 +10,7 @@ import org.springframework.boot.test.SpringApplicationConfiguration;
 import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.Tracer;
 import org.springframework.cloud.sleuth.instrument.DefaultTestAutoConfiguration;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.scheduling.annotation.Async;
@@ -61,7 +61,7 @@ public class TraceAsyncIntegrationTests {
 
 	@After
 	public void cleanTrace() {
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@DefaultTestAutoConfiguration
@@ -82,7 +82,7 @@ public class TraceAsyncIntegrationTests {
 
 		@Async
 		public void invokeAsynchronousLogic() {
-			this.span.set(SpanContextHolder.getCurrentSpan());
+			this.span.set(TestSpanContextHolder.getCurrentSpan());
 		}
 
 		public Long getTraceId() {

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/web/TraceFilterMockChainIntegrationTests.java

@@ -24,7 +24,7 @@ import org.springframework.cloud.sleuth.Tracer;
 import org.springframework.cloud.sleuth.instrument.TraceKeys;
 import org.springframework.cloud.sleuth.sampler.AlwaysSampler;
 import org.springframework.cloud.sleuth.trace.DefaultTracer;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.support.StaticApplicationContext;
 import org.springframework.http.MediaType;
 import org.springframework.mock.web.MockFilterChain;
@@ -57,7 +57,7 @@ public class TraceFilterMockChainIntegrationTests {
 	@Before
 	@SneakyThrows
 	public void init() {
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 		this.context.refresh();
 		this.request = builder().buildRequest(new MockServletContext());
 		this.response = new MockHttpServletResponse();
@@ -74,7 +74,7 @@ public class TraceFilterMockChainIntegrationTests {
 	public void startsNewTrace() throws Exception {
 		TraceFilter filter = new TraceFilter(this.tracer, this.traceKeys);
 		filter.doFilter(this.request, this.response, this.filterChain);
-		assertNull(SpanContextHolder.getCurrentSpan());
+		assertNull(TestSpanContextHolder.getCurrentSpan());
 	}
 
 	@Test
@@ -84,7 +84,7 @@ public class TraceFilterMockChainIntegrationTests {
 				.header(Span.TRACE_ID_NAME, generator.nextLong()).buildRequest(new MockServletContext());
 		TraceFilter filter = new TraceFilter(this.tracer, this.traceKeys);
 		filter.doFilter(this.request, this.response, this.filterChain);
-		assertNull(SpanContextHolder.getCurrentSpan());
+		assertNull(TestSpanContextHolder.getCurrentSpan());
 	}
 
 }

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/web/TraceFilterTests.java

@@ -34,9 +34,9 @@ import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.Tracer;
 import org.springframework.cloud.sleuth.instrument.TraceKeys;
 import org.springframework.cloud.sleuth.sampler.AlwaysSampler;
-import org.springframework.cloud.sleuth.sampler.IsTracingSampler;
+import org.springframework.cloud.sleuth.sampler.NeverSampler;
 import org.springframework.cloud.sleuth.trace.DefaultTracer;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.MediaType;
@@ -91,7 +91,7 @@ public class TraceFilterTests {
 
 	@Test
 	public void notTraced() throws Exception {
-		this.sampler = new IsTracingSampler();
+		this.sampler = NeverSampler.INSTANCE;
 		TraceFilter filter = new TraceFilter(this.tracer, this.traceKeys);
 
 		this.request = get("/favicon.ico").accept(MediaType.ALL)
@@ -100,7 +100,7 @@ public class TraceFilterTests {
 		filter.doFilter(this.request, this.response, this.filterChain);
 
 		assertFalse(this.span.isExportable());
-		assertNull(SpanContextHolder.getCurrentSpan());
+		assertNull(TestSpanContextHolder.getCurrentSpan());
 	}
 
 	@Test
@@ -108,7 +108,7 @@ public class TraceFilterTests {
 		TraceFilter filter = new TraceFilter(this.tracer, this.traceKeys);
 		filter.doFilter(this.request, this.response, this.filterChain);
 		verifyHttpTags();
-		assertNull(SpanContextHolder.getCurrentSpan());
+		assertNull(TestSpanContextHolder.getCurrentSpan());
 	}
 
 	@Test
@@ -117,14 +117,14 @@ public class TraceFilterTests {
 		Span span = this.tracer.startTrace("foo");
 		this.request.setAttribute(TraceFilter.TRACE_REQUEST_ATTR, span);
 		// It should have been removed from the thread local context so simulate that
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 
 		TraceFilter filter = new TraceFilter(this.tracer, this.traceKeys);
 		filter.doFilter(this.request, this.response, this.filterChain);
 
 		verifyHttpTags();
 
-		assertNull(SpanContextHolder.getCurrentSpan());
+		assertNull(TestSpanContextHolder.getCurrentSpan());
 	}
 
 	@Test
@@ -137,7 +137,7 @@ public class TraceFilterTests {
 
 		verifyHttpTags();
 
-		assertNull(SpanContextHolder.getCurrentSpan());
+		assertNull(TestSpanContextHolder.getCurrentSpan());
 	}
 
 	@Test
@@ -152,7 +152,7 @@ public class TraceFilterTests {
 
 		assertThat(this.span.tags()).contains(entry("http.x-foo", "bar"));
 
-		assertNull(SpanContextHolder.getCurrentSpan());
+		assertNull(TestSpanContextHolder.getCurrentSpan());
 	}
 
 	@Test
@@ -168,7 +168,7 @@ public class TraceFilterTests {
 
 		assertThat(this.span.tags()).contains(entry("http.x-foo", "'bar','spam'"));
 
-		assertNull(SpanContextHolder.getCurrentSpan());
+		assertNull(TestSpanContextHolder.getCurrentSpan());
 	}
 
 	@Test
@@ -190,7 +190,7 @@ public class TraceFilterTests {
 		}
 		verifyHttpTags(HttpStatus.INTERNAL_SERVER_ERROR);
 
-		assertNull(SpanContextHolder.getCurrentSpan());
+		assertNull(TestSpanContextHolder.getCurrentSpan());
 	}
 
 	public void verifyHttpTags() {

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/web/client/FeignTraceTests.java

@@ -24,7 +24,7 @@ import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.Tracer;
 import org.springframework.cloud.sleuth.event.ClientReceivedEvent;
 import org.springframework.cloud.sleuth.event.ClientSentEvent;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
@@ -60,7 +60,7 @@ public class FeignTraceTests {
 
 	@After
 	public void close() {
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 		this.listener.getEvents().clear();
 	}
 

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/web/client/TraceRestTemplateInterceptorTests.java

@@ -30,7 +30,7 @@ import org.junit.Test;
 import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.sampler.AlwaysSampler;
 import org.springframework.cloud.sleuth.trace.DefaultTracer;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.support.StaticApplicationContext;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.client.ClientHttpRequestInterceptor;
@@ -64,12 +64,12 @@ public class TraceRestTemplateInterceptorTests {
 		this.traces = new DefaultTracer(new AlwaysSampler(), new Random(), this.publisher);
 		this.template.setInterceptors(Arrays.<ClientHttpRequestInterceptor>asList(
 				new TraceRestTemplateInterceptor(this.traces)));
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@After
 	public void clean() {
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@Test

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/zuul/TracePostZuulFilterTests.java

@@ -28,7 +28,7 @@ import org.mockito.Mockito;
 import org.springframework.cloud.sleuth.event.ClientReceivedEvent;
 import org.springframework.cloud.sleuth.sampler.AlwaysSampler;
 import org.springframework.cloud.sleuth.trace.DefaultTracer;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.ApplicationEventPublisher;
 
 import com.netflix.zuul.context.RequestContext;
@@ -49,7 +49,7 @@ public class TracePostZuulFilterTests {
 	@Before
 	public void clean() {
 		RequestContext.getCurrentContext().unset();
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@Test

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/instrument/zuul/TracePreZuulFilterTests.java

@@ -29,9 +29,9 @@ import org.junit.Test;
 import org.mockito.Mockito;
 import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.sampler.AlwaysSampler;
-import org.springframework.cloud.sleuth.sampler.IsTracingSampler;
+import org.springframework.cloud.sleuth.sampler.NeverSampler;
 import org.springframework.cloud.sleuth.trace.DefaultTracer;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.ApplicationEventPublisher;
 
 import com.netflix.zuul.context.RequestContext;
@@ -42,9 +42,11 @@ import com.netflix.zuul.context.RequestContext;
  */
 public class TracePreZuulFilterTests {
 
-	private ApplicationEventPublisher publisher = Mockito.mock(ApplicationEventPublisher.class);
+	private ApplicationEventPublisher publisher = Mockito
+			.mock(ApplicationEventPublisher.class);
 
-	private DefaultTracer tracer = new DefaultTracer(new AlwaysSampler(), new Random(), this.publisher);
+	private DefaultTracer tracer = new DefaultTracer(new AlwaysSampler(), new Random(),
+			this.publisher);
 
 	private TracePreZuulFilter filter = new TracePreZuulFilter(this.tracer);
 
@@ -52,7 +54,7 @@ public class TracePreZuulFilterTests {
 	@Before
 	public void clean() {
 		RequestContext.getCurrentContext().unset();
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@Test
@@ -60,17 +62,21 @@ public class TracePreZuulFilterTests {
 		this.tracer.startTrace("start");
 		this.filter.run();
 		RequestContext ctx = RequestContext.getCurrentContext();
-		assertThat(ctx.getZuulRequestHeaders().get(Span.TRACE_ID_NAME), is(notNullValue()));
-		assertThat(ctx.getZuulRequestHeaders().get(Span.NOT_SAMPLED_NAME), is(nullValue()));
+		assertThat(ctx.getZuulRequestHeaders().get(Span.TRACE_ID_NAME),
+				is(notNullValue()));
+		assertThat(ctx.getZuulRequestHeaders().get(Span.NOT_SAMPLED_NAME),
+				is(nullValue()));
 	}
 
 	@Test
 	public void notSampledIfNotExportable() throws Exception {
-		this.tracer.startTrace("start", new IsTracingSampler());
+		this.tracer.startTrace("start", NeverSampler.INSTANCE);
 		this.filter.run();
 		RequestContext ctx = RequestContext.getCurrentContext();
-		assertThat(ctx.getZuulRequestHeaders().get(Span.TRACE_ID_NAME), is(notNullValue()));
-		assertThat(ctx.getZuulRequestHeaders().get(Span.NOT_SAMPLED_NAME), is(notNullValue()));
+		assertThat(ctx.getZuulRequestHeaders().get(Span.TRACE_ID_NAME),
+				is(notNullValue()));
+		assertThat(ctx.getZuulRequestHeaders().get(Span.NOT_SAMPLED_NAME),
+				is(notNullValue()));
 	}
 
 }

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/template/TraceTemplateTests.java

@@ -7,7 +7,7 @@ import org.springframework.cloud.sleuth.Span;
 import org.springframework.cloud.sleuth.Tracer;
 import org.springframework.cloud.sleuth.sampler.AlwaysSampler;
 import org.springframework.cloud.sleuth.trace.DefaultTracer;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.trace.TestSpanContextHolder;
 import org.springframework.context.ApplicationEventPublisher;
 
 import java.util.Random;
@@ -21,7 +21,7 @@ public class TraceTemplateTests {
 
 	@After
 	public void close() {
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@Test
@@ -39,7 +39,7 @@ public class TraceTemplateTests {
 		return traceTemplate.trace(new TraceCallback<Span>() {
 				@Override
 				public Span doInTrace(Span span) {
-					return SpanContextHolder.getCurrentSpan();
+					return TestSpanContextHolder.getCurrentSpan();
 				}
 			});
 	}

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/trace/DefaultTracerTests.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-package org.springframework.cloud.sleuth;
+package org.springframework.cloud.sleuth.trace;
 
 import static org.hamcrest.CoreMatchers.equalTo;
 import static org.hamcrest.Matchers.is;
@@ -33,12 +33,12 @@ import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
 import org.mockito.ArgumentCaptor;
+import org.springframework.cloud.sleuth.Span;
+import org.springframework.cloud.sleuth.Tracer;
 import org.springframework.cloud.sleuth.event.SpanAcquiredEvent;
 import org.springframework.cloud.sleuth.event.SpanReleasedEvent;
 import org.springframework.cloud.sleuth.sampler.AlwaysSampler;
-import org.springframework.cloud.sleuth.sampler.IsTracingSampler;
-import org.springframework.cloud.sleuth.trace.DefaultTracer;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
+import org.springframework.cloud.sleuth.sampler.NeverSampler;
 import org.springframework.context.ApplicationEvent;
 import org.springframework.context.ApplicationEventPublisher;
 
@@ -55,19 +55,20 @@ public class DefaultTracerTests {
 
 	@Before
 	public void setup() {
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 		this.publisher = mock(ApplicationEventPublisher.class);
 	}
 
 	@After
 	public void clean() {
-		SpanContextHolder.removeCurrentSpan();
+		TestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@Test
 	public void tracingWorks() {
 
-		DefaultTracer tracer = new DefaultTracer(new IsTracingSampler(), new Random(), this.publisher);
+		DefaultTracer tracer = new DefaultTracer(NeverSampler.INSTANCE, new Random(),
+				this.publisher);
 
 		Span span = tracer.startTrace(CREATE_SIMPLE_TRACE, new AlwaysSampler());
 		try {
@@ -77,8 +78,10 @@ public class DefaultTracerTests {
 			tracer.close(span);
 		}
 
-		verify(this.publisher, times(NUM_SPANS)).publishEvent(isA(SpanAcquiredEvent.class));
-		verify(this.publisher, times(NUM_SPANS)).publishEvent(isA(SpanReleasedEvent.class));
+		verify(this.publisher, times(NUM_SPANS))
+				.publishEvent(isA(SpanAcquiredEvent.class));
+		verify(this.publisher, times(NUM_SPANS))
+				.publishEvent(isA(SpanReleasedEvent.class));
 
 		ArgumentCaptor<ApplicationEvent> captor = ArgumentCaptor
 				.forClass(ApplicationEvent.class);
@@ -103,22 +106,25 @@ public class DefaultTracerTests {
 
 	@Test
 	public void nonExportable() {
-		DefaultTracer tracer = new DefaultTracer(new IsTracingSampler(), new Random(), this.publisher);
+		DefaultTracer tracer = new DefaultTracer(NeverSampler.INSTANCE, new Random(),
+				this.publisher);
 		Span span = tracer.startTrace(CREATE_SIMPLE_TRACE);
 		assertThat(span.isExportable(), is(false));
 	}
 
 	@Test
 	public void exportable() {
-		DefaultTracer tracer = new DefaultTracer(new AlwaysSampler(), new Random(), this.publisher);
+		DefaultTracer tracer = new DefaultTracer(new AlwaysSampler(), new Random(),
+				this.publisher);
 		Span span = tracer.startTrace(CREATE_SIMPLE_TRACE);
 		assertThat(span.isExportable(), is(true));
 	}
 
 	@Test
 	public void exportableInheritedFromParent() {
-		DefaultTracer tracer = new DefaultTracer(new AlwaysSampler(), new Random(), this.publisher);
-		Span span = tracer.startTrace(CREATE_SIMPLE_TRACE, new IsTracingSampler());
+		DefaultTracer tracer = new DefaultTracer(new AlwaysSampler(), new Random(),
+				this.publisher);
+		Span span = tracer.startTrace(CREATE_SIMPLE_TRACE, NeverSampler.INSTANCE);
 		assertThat(span.isExportable(), is(false));
 		Span child = tracer.joinTrace(CREATE_SIMPLE_TRACE + "/child", span);
 		assertThat(child.isExportable(), is(false));
@@ -126,7 +132,8 @@ public class DefaultTracerTests {
 
 	@Test
 	public void parentNotRemovedIfActiveOnJoin() {
-		DefaultTracer tracer = new DefaultTracer(new AlwaysSampler(), new Random(), this.publisher);
+		DefaultTracer tracer = new DefaultTracer(new AlwaysSampler(), new Random(),
+				this.publisher);
 		Span parent = tracer.startTrace(CREATE_SIMPLE_TRACE);
 		Span span = tracer.joinTrace(IMPORTANT_WORK_1, parent);
 		tracer.close(span);
@@ -135,8 +142,10 @@ public class DefaultTracerTests {
 
 	@Test
 	public void parentRemovedIfNotActiveOnJoin() {
-		DefaultTracer tracer = new DefaultTracer(new AlwaysSampler(), new Random(), this.publisher);
-		Span parent = Span.builder().name(CREATE_SIMPLE_TRACE).traceId(1L).spanId(1L).build();
+		DefaultTracer tracer = new DefaultTracer(new AlwaysSampler(), new Random(),
+				this.publisher);
+		Span parent = Span.builder().name(CREATE_SIMPLE_TRACE).traceId(1L).spanId(1L)
+				.build();
 		Span span = tracer.joinTrace(IMPORTANT_WORK_1, parent);
 		tracer.close(span);
 		assertThat(tracer.getCurrentSpan(), is(equalTo(null)));
@@ -144,9 +153,11 @@ public class DefaultTracerTests {
 
 	@Test
 	public void grandParentRestoredAfterAutoClose() {
-		DefaultTracer tracer = new DefaultTracer(new AlwaysSampler(), new Random(), this.publisher);
+		DefaultTracer tracer = new DefaultTracer(new AlwaysSampler(), new Random(),
+				this.publisher);
 		Span grandParent = tracer.startTrace(CREATE_SIMPLE_TRACE);
-		Span parent = Span.builder().name(IMPORTANT_WORK_1).traceId(1L).spanId(1L).build();
+		Span parent = Span.builder().name(IMPORTANT_WORK_1).traceId(1L).spanId(1L)
+				.build();
 		Span span = tracer.joinTrace(IMPORTANT_WORK_2, parent);
 		tracer.close(span);
 		assertThat(tracer.getCurrentSpan(), is(equalTo(grandParent)));
@@ -156,8 +167,8 @@ public class DefaultTracerTests {
 		List<Span> found = findSpans(spans, parentId);
 		assertThat("more than one span with parentId " + parentId, found.size(), is(1));
 		Span span = found.get(0);
-		assertThat("name is wrong for span with parentId " + parentId,
-				span.getName(), is(name));
+		assertThat("name is wrong for span with parentId " + parentId, span.getName(),
+				is(name));
 		return span;
 	}
 

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/trace/TestSpanContextHolder.java

@@ -0,0 +1,40 @@
+/*
+ * Copyright 2013-2015 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.sleuth.trace;
+
+import org.springframework.cloud.sleuth.Span;
+
+/**
+ * Test utility to access the thread context provided by the (private)
+ * {@link SpanContextHolder}.
+ *
+ * @author Dave Syer
+ */
+public class TestSpanContextHolder {
+
+	public static Span getCurrentSpan() {
+		return SpanContextHolder.getCurrentSpan();
+	}
+
+	public static void removeCurrentSpan() {
+		SpanContextHolder.removeCurrentSpan();
+	}
+
+	public static boolean isTracing() {
+		return SpanContextHolder.isTracing();
+	}
+}

spring-cloud-sleuth-samples/spring-cloud-sleuth-sample-test-core/src/main/java/org/springframework/cloud/sleuth/trace/IntegrationTestSpanContextHolder.java

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2013-2015 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.cloud.sleuth.trace;
+
+import org.springframework.cloud.sleuth.Span;
+
+/**
+ * @author Spencer Gibb
+ */
+public class IntegrationTestSpanContextHolder {
+
+	public static Span getCurrentSpan() {
+		return SpanContextHolder.getCurrentSpan();
+	}
+
+	public static void removeCurrentSpan() {
+		SpanContextHolder.removeCurrentSpan();
+	}
+
+	public static boolean isTracing() {
+		return SpanContextHolder.isTracing();
+	}
+}

spring-cloud-sleuth-samples/spring-cloud-sleuth-sample-test-core/src/main/java/tools/AbstractIntegrationTest.java

@@ -15,24 +15,34 @@
  */
 package tools;
 
-import com.jayway.awaitility.Awaitility;
-import com.jayway.awaitility.core.ConditionFactory;
-import lombok.extern.slf4j.Slf4j;
-import org.junit.After;
-import org.junit.Before;
-import org.springframework.cloud.sleuth.trace.SpanContextHolder;
-import org.springframework.http.*;
-import org.springframework.web.client.RestTemplate;
-import zipkin.Codec;
-import zipkin.Span;
-
-import java.net.URI;
-import java.util.*;
-import java.util.stream.Collectors;
-
 import static java.util.concurrent.TimeUnit.SECONDS;
 import static org.assertj.core.api.BDDAssertions.then;
 
+import java.net.URI;
+import java.util.ArrayList;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.List;
+import java.util.Optional;
+import java.util.stream.Collectors;
+
+import org.junit.After;
+import org.junit.Before;
+import org.springframework.cloud.sleuth.trace.IntegrationTestSpanContextHolder;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.RequestEntity;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.client.RestTemplate;
+
+import com.jayway.awaitility.Awaitility;
+import com.jayway.awaitility.core.ConditionFactory;
+
+import lombok.extern.slf4j.Slf4j;
+import zipkin.Codec;
+import zipkin.Span;
+
 /**
  * @author Marcin Grzejszczak
  */
@@ -45,12 +55,12 @@ public abstract class AbstractIntegrationTest {
 
 	@Before
 	public void clearSpanBefore() {
-		SpanContextHolder.removeCurrentSpan();
+		IntegrationTestSpanContextHolder.removeCurrentSpan();
 	}
 
 	@After
 	public void clearSpanAfter() {
-		SpanContextHolder.removeCurrentSpan();
+		IntegrationTestSpanContextHolder.removeCurrentSpan();
 	}
 
 	public static ConditionFactory await() {

spring-cloud-sleuth-samples/spring-cloud-sleuth-sample-test-core/src/main/java/tools/RequestSendingRunnable.java

@@ -15,7 +15,11 @@
  */
 package tools;
 
-import lombok.extern.slf4j.Slf4j;
+import static org.assertj.core.api.BDDAssertions.then;
+
+import java.net.URI;
+import java.util.Random;
+
 import org.springframework.cloud.sleuth.Span;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
@@ -24,10 +28,7 @@ import org.springframework.http.RequestEntity;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.client.RestTemplate;
 
-import java.net.URI;
-import java.util.Random;
-
-import static org.assertj.core.api.BDDAssertions.then;
+import lombok.extern.slf4j.Slf4j;
 
 /**
  * Runnable that will send a request via the provide rest template to the
@@ -60,12 +61,12 @@ public class RequestSendingRunnable implements Runnable {
 		log.info("Received the following response [{}]", responseEntity);
 	}
 
-	private RequestEntity requestWithTraceId() {
+	private RequestEntity<Void> requestWithTraceId() {
 		HttpHeaders headers = new HttpHeaders();
 		headers.add(Span.TRACE_ID_NAME, Span.toHex(this.traceId));
 		headers.add(Span.SPAN_ID_NAME, Span.toHex(this.spanId));
 		URI uri = URI.create(this.url);
-		RequestEntity requestEntity = new RequestEntity<>(headers, HttpMethod.GET, uri);
+		RequestEntity<Void> requestEntity = new RequestEntity<>(headers, HttpMethod.GET, uri);
 		log.info("Request [" + requestEntity + "] is ready");
 		return requestEntity;
 	}