Avoid unnecessarily alarming stack trace logged during scheduler resolution

Closes gh-23268

Author: jhoeller

spring-context/src/main/java/org/springframework/scheduling/annotation/ScheduledAnnotationBeanPostProcessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 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.
@@ -256,7 +256,10 @@ private void finishRegistration() {
 				this.registrar.setTaskScheduler(resolveSchedulerBean(this.beanFactory, TaskScheduler.class, false));
 			}
 			catch (NoUniqueBeanDefinitionException ex) {
-				logger.trace("Could not find unique TaskScheduler bean", ex);
+				if (logger.isTraceEnabled()) {
+					logger.trace("Could not find unique TaskScheduler bean - attempting to resolve by name: " +
+							ex.getMessage());
+				}
 				try {
 					this.registrar.setTaskScheduler(resolveSchedulerBean(this.beanFactory, TaskScheduler.class, true));
 				}
@@ -271,13 +274,19 @@ private void finishRegistration() {
 				}
 			}
 			catch (NoSuchBeanDefinitionException ex) {
-				logger.trace("Could not find default TaskScheduler bean", ex);
+				if (logger.isTraceEnabled()) {
+					logger.trace("Could not find default TaskScheduler bean - attempting to find ScheduledExecutorService: " +
+							ex.getMessage());
+				}
 				// Search for ScheduledExecutorService bean next...
 				try {
 					this.registrar.setScheduler(resolveSchedulerBean(this.beanFactory, ScheduledExecutorService.class, false));
 				}
 				catch (NoUniqueBeanDefinitionException ex2) {
-					logger.trace("Could not find unique ScheduledExecutorService bean", ex2);
+					if (logger.isTraceEnabled()) {
+						logger.trace("Could not find unique ScheduledExecutorService bean - attempting to resolve by name: " +
+								ex2.getMessage());
+					}
 					try {
 						this.registrar.setScheduler(resolveSchedulerBean(this.beanFactory, ScheduledExecutorService.class, true));
 					}
@@ -292,7 +301,10 @@ private void finishRegistration() {
 					}
 				}
 				catch (NoSuchBeanDefinitionException ex2) {
-					logger.trace("Could not find default ScheduledExecutorService bean", ex2);
+					if (logger.isTraceEnabled()) {
+						logger.trace("Could not find default ScheduledExecutorService bean - falling back to default: " +
+								ex2.getMessage());
+					}
 					// Giving up -> falling back to default scheduler within the registrar...
 					logger.info("No TaskScheduler/ScheduledExecutorService bean found for scheduled processing");
 				}