Updated documentation

docs/src/main/asciidoc/intro.adoc

@@ -417,6 +417,18 @@ dependencies {
 <2> Add the dependency to `spring-cloud-starter-zipkin`. That way, all nested dependencies get downloaded.
 <3> To automatically configure RabbitMQ, add the `spring-rabbit` dependency.
 
+=== Overriding the auto-configuration of Zipkin
+
+Spring Cloud Sleuth supports sending traces to multiple tracing systems as of version 2.1.0.
+In order to get this to work, every tracing system needs to have a `Reporter<Span>` and `Sender`.
+If you want to override the provided beans you need to give them a specific name.
+To do this you can use respectively `ZipkinAutoConfiguration.REPORTER_BEAN_NAME` and `ZipkinAutoConfiguration.SENDER_BEAN_NAME`.
+
+[source,java]
+----
+include::../../../../spring-cloud-sleuth-zipkin/src/test/java/org/springframework/cloud/sleuth/zipkin2/ZipkinAutoConfigurationTests.java[tags=override_default_beans,indent=0]
+----
+
 == Additional Resources
 
 You can watch a video of https://twitter.com/reshmi9k[Reshmi Krishna] and https://twitter.com/mgrzejszczak[Marcin Grzejszczak] talking about Spring Cloud

spring-cloud-sleuth-zipkin/src/test/java/org/springframework/cloud/sleuth/zipkin2/ZipkinAutoConfigurationTests.java

@@ -203,12 +203,12 @@ public class ZipkinAutoConfigurationTests {
 		this.context.refresh();
 
 		then(this.context.getBeansOfType(Sender.class)).hasSize(2);
-		then(this.context.getBeansOfType(Sender.class)).containsKeys("zipkinSender",
+		then(this.context.getBeansOfType(Sender.class))
-				"otherSender");
+				.containsKeys(ZipkinAutoConfiguration.SENDER_BEAN_NAME, "otherSender");
 
 		then(this.context.getBeansOfType(Reporter.class)).hasSize(2);
-		then(this.context.getBeansOfType(Reporter.class)).containsKeys("zipkinReporter",
+		then(this.context.getBeansOfType(Reporter.class)).containsKeys(
-				"otherReporter");
+				ZipkinAutoConfiguration.REPORTER_BEAN_NAME, "otherReporter");
 
 		Span span = this.context.getBean(Tracing.class).tracer().nextSpan().name("foo")
 				.tag("foo", "bar").start();
@@ -226,6 +226,34 @@ public class ZipkinAutoConfigurationTests {
 		Awaitility.await().untilAsserted(() -> then(sender.isSpanSent()).isTrue());
 	}
 
+	@Test
+	public void shouldOverrideDefaultBeans() {
+		this.context = new AnnotationConfigApplicationContext();
+		this.context.register(ZipkinAutoConfiguration.class,
+				PropertyPlaceholderAutoConfiguration.class, TraceAutoConfiguration.class,
+				Config.class, MyConfig.class);
+		this.context.refresh();
+
+		then(this.context.getBeansOfType(Sender.class)).hasSize(1);
+		then(this.context.getBeansOfType(Sender.class))
+				.containsKeys(ZipkinAutoConfiguration.SENDER_BEAN_NAME);
+
+		then(this.context.getBeansOfType(Reporter.class)).hasSize(1);
+		then(this.context.getBeansOfType(Reporter.class))
+				.containsKeys(ZipkinAutoConfiguration.REPORTER_BEAN_NAME);
+
+		Span span = this.context.getBean(Tracing.class).tracer().nextSpan().name("foo")
+				.tag("foo", "bar").start();
+
+		span.finish();
+
+		Awaitility.await()
+				.untilAsserted(() -> then(this.server.getRequestCount()).isEqualTo(0));
+
+		MyConfig.MySender sender = this.context.getBean(MyConfig.MySender.class);
+		Awaitility.await().untilAsserted(() -> then(sender.isSpanSent()).isTrue());
+	}
+
 	@Configuration
 	protected static class Config {
 
@@ -309,4 +337,54 @@ public class ZipkinAutoConfigurationTests {
 
 	}
 
+	// tag::override_default_beans[]
+
+	@Configuration
+	protected static class MyConfig {
+
+		@Bean(ZipkinAutoConfiguration.REPORTER_BEAN_NAME)
+		Reporter<zipkin2.Span> myReporter() {
+			return AsyncReporter.create(mySender());
+		}
+
+		@Bean(ZipkinAutoConfiguration.SENDER_BEAN_NAME)
+		MySender mySender() {
+			return new MySender();
+		}
+
+		static class MySender extends Sender {
+
+			private boolean spanSent = false;
+
+			boolean isSpanSent() {
+				return this.spanSent;
+			}
+
+			@Override
+			public Encoding encoding() {
+				return Encoding.JSON;
+			}
+
+			@Override
+			public int messageMaxBytes() {
+				return Integer.MAX_VALUE;
+			}
+
+			@Override
+			public int messageSizeInBytes(List<byte[]> encodedSpans) {
+				return encoding().listSizeInBytes(encodedSpans);
+			}
+
+			@Override
+			public Call<Void> sendSpans(List<byte[]> encodedSpans) {
+				this.spanSent = true;
+				return Call.create(null);
+			}
+
+		}
+
+	}
+
+	// end::override_default_beans[]
+
 }