Make auto-configured BatchSpanProcessor back off when the user defines their own

Closes gh-44601

Author: mhalbritter

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/tracing/OpenTelemetryTracingAutoConfiguration.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -115,6 +115,7 @@ SpanProcessors spanProcessors(ObjectProvider<SpanProcessor> spanProcessors) {
 	}
 
 	@Bean
+	@ConditionalOnMissingBean
 	BatchSpanProcessor otelSpanProcessor(SpanExporters spanExporters,
 			ObjectProvider<SpanExportingPredicate> spanExportingPredicates, ObjectProvider<SpanReporter> spanReporters,
 			ObjectProvider<SpanFilter> spanFilters, ObjectProvider<MeterProvider> meterProvider) {

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/tracing/OpenTelemetryTracingAutoConfigurationTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2024 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -51,6 +51,7 @@
 import io.opentelemetry.sdk.trace.SpanLimits;
 import io.opentelemetry.sdk.trace.SpanProcessor;
 import io.opentelemetry.sdk.trace.data.SpanData;
+import io.opentelemetry.sdk.trace.export.BatchSpanProcessor;
 import io.opentelemetry.sdk.trace.export.SpanExporter;
 import io.opentelemetry.sdk.trace.samplers.Sampler;
 import org.assertj.core.api.InstanceOfAssertFactories;
@@ -172,6 +173,8 @@ void shouldBackOffOnCustomBeans() {
 			assertThat(context).hasSingleBean(SpanProcessors.class);
 			assertThat(context).hasBean("customSpanExporters");
 			assertThat(context).hasSingleBean(SpanExporters.class);
+			assertThat(context).hasBean("customBatchSpanProcessor");
+			assertThat(context).hasSingleBean(BatchSpanProcessor.class);
 		});
 	}
 
@@ -401,6 +404,11 @@ SpanExporter spanExporter2() {
 	@Configuration(proxyBeanMethods = false)
 	private static final class CustomConfiguration {
 
+		@Bean
+		BatchSpanProcessor customBatchSpanProcessor() {
+			return mock(BatchSpanProcessor.class);
+		}
+
 		@Bean
 		SpanProcessors customSpanProcessors() {
 			return SpanProcessors.of(mock(SpanProcessor.class));