Fixes the case where the sender is overriden with the predefined name; fixes gh-1637

spring-cloud-sleuth-zipkin/src/main/java/org/springframework/cloud/sleuth/zipkin2/ZipkinBackwardsCompatibilityAutoConfiguration.java

@@ -98,7 +98,10 @@ public class ZipkinBackwardsCompatibilityAutoConfiguration {
 				DefaultListableBeanFactory beanFactory) {
 			List<String> beanNames = new ArrayList<>(
 					Arrays.asList(beanFactory.getBeanNamesForType(Sender.class)));
-			beanNames.remove(ZipkinAutoConfiguration.SENDER_BEAN_NAME);
+			if (beanNames.size() != 1
+					|| !beanNames.contains(ZipkinAutoConfiguration.SENDER_BEAN_NAME)) {
+				beanNames.remove(ZipkinAutoConfiguration.SENDER_BEAN_NAME);
+			}
 			Sender sender = (Sender) beanFactory.getBean(beanNames.get(0));
 			// historical constraint. Note: AsyncReporter supports memory bounds
 			return AsyncReporter.builder(sender).queuedMaxSpans(1000)
@@ -145,18 +148,23 @@ public class ZipkinBackwardsCompatibilityAutoConfiguration {
 					context.getBeanFactory());
 			DefaultListableBeanFactory listableBeanFactory = (DefaultListableBeanFactory) context
 					.getBeanFactory();
-			int foundSenders = listableBeanFactory
-					.getBeanNamesForType(Sender.class).length;
+			String[] foundSenders = listableBeanFactory.getBeanNamesForType(Sender.class);
+			int foundSendersSize = foundSenders.length;
 
 			// Previously we supported 1 Sender bean at a time
 			// which could be overridden by another auto-configuration.
 			// Now we support both the overridden bean and our default zipkinSender bean.
 			// Since this config is adapting the old config we're searching for exactly 1
 			// `Sender` bean before `ZipkinAutoConfiguration` kicks in.
-			if (foundSenders != 1) {
+			if (foundSendersSize != 1) {
 				return ConditionOutcome.noMatch(
 						"None or multiple Sender beans found - no reason to apply backwards compatibility");
 			}
+			else if (foundSenders[0].equals(ZipkinAutoConfiguration.SENDER_BEAN_NAME)) {
+				return ConditionOutcome.noMatch("A single, ["
+						+ ZipkinAutoConfiguration.SENDER_BEAN_NAME
+						+ "] named bean found - no reason to apply backwards compatibility");
+			}
 			int foundReporters = listableBeanFactory
 					.getBeanNamesForType(Reporter.class).length;
 			// Check if we need to provide a Reporter bean for the overridden Sender bean

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

@@ -16,15 +16,23 @@
 
 package org.springframework.cloud.sleuth.zipkin2;
 
+import java.util.List;
+
 import org.junit.Test;
+import zipkin2.Call;
 import zipkin2.codec.BytesEncoder;
+import zipkin2.codec.Encoding;
+import zipkin2.reporter.AsyncReporter;
 import zipkin2.reporter.InMemoryReporterMetrics;
 import zipkin2.reporter.Reporter;
 import zipkin2.reporter.ReporterMetrics;
+import zipkin2.reporter.Sender;
 
 import org.springframework.boot.autoconfigure.AutoConfigurations;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
 import org.springframework.cloud.sleuth.autoconfig.TraceAutoConfiguration;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -71,4 +79,50 @@ public class ZipkinBackwardsCompatibilityAutoConfigurationTests {
 				});
 	}
 
+	@Test
+	public void shouldAllowOverridingSenderOnlyWithoutOverridingTheReporter() {
+		this.contextRunner.withUserConfiguration(MyConfig.class).run(context -> {
+			assertThat(context.getBean(ZipkinProperties.class)).isNotNull();
+			assertThat(context.getBean(Reporter.class)).isInstanceOf(AsyncReporter.class);
+			assertThat(context.getBean(Sender.class)).isInstanceOf(MySender.class);
+			assertThat(context.getBean(BytesEncoder.class)).isNotNull();
+			assertThat(context.getBean(ReporterMetrics.class))
+					.isInstanceOf(InMemoryReporterMetrics.class);
+		});
+	}
+
+	@Configuration
+	protected static class MyConfig {
+
+		@Bean(ZipkinAutoConfiguration.SENDER_BEAN_NAME)
+		Sender mySender() {
+			return new MySender();
+		}
+
+	}
+
+	static class MySender extends Sender {
+
+		@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) {
+			return Call.create(null);
+		}
+
+	}
+
 }