Fix `QuartzAutoConfigurtion` failure with multiple `Executor` beans

`QuartzAutoConfigurtion` currently blows up if there are multiple
`Executor` beans in the context.

This commit changes the configuration to retrieve `Executor` bean using
`ObjectProvider#getIfUnique` which won't fail in scenarios where there
are multiple `Executor` beans with none marked as `@Primary`.

Closes gh-9434

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/quartz/QuartzAutoConfiguration.java

@@ -81,7 +81,7 @@ public class QuartzAutoConfiguration {
 			ObjectProvider<Trigger[]> triggers, ApplicationContext applicationContext) {
 		this.properties = properties;
 		this.customizers = customizers.getIfAvailable();
-		this.taskExecutor = taskExecutor.getIfAvailable();
+		this.taskExecutor = taskExecutor.getIfUnique();
 		this.jobDetails = jobDetails.getIfAvailable();
 		this.calendars = calendars.getIfAvailable();
 		this.triggers = triggers.getIfAvailable();

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/quartz/QuartzAutoConfigurationTests.java

@@ -40,6 +40,7 @@ import org.quartz.TriggerKey;
 import org.quartz.impl.calendar.MonthlyCalendar;
 import org.quartz.impl.calendar.WeeklyCalendar;
 import org.quartz.simpl.RAMJobStore;
+import org.quartz.simpl.SimpleThreadPool;
 
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration;
@@ -51,6 +52,7 @@ import org.springframework.context.annotation.AnnotationConfigApplicationContext
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Import;
+import org.springframework.context.annotation.Primary;
 import org.springframework.core.env.Environment;
 import org.springframework.jdbc.core.JdbcTemplate;
 import org.springframework.scheduling.quartz.LocalDataSourceJobStore;
@@ -145,6 +147,36 @@ public class QuartzAutoConfigurationTests {
 				.isEqualTo(LocalTaskExecutorThreadPool.class);
 	}
 
+	@Test
+	public void withMultipleTaskExecutors() throws Exception {
+		load(QuartzMultipleExecutorsConfiguration.class);
+		assertThat(this.context.getBeansOfType(Executor.class)).hasSize(2);
+		assertThat(this.context.getBeansOfType(Scheduler.class)).hasSize(1);
+		Scheduler scheduler = this.context.getBean(Scheduler.class);
+		assertThat(scheduler.getMetaData().getThreadPoolClass())
+				.isEqualTo(SimpleThreadPool.class);
+	}
+
+	@Test
+	public void withMultipleTaskExecutorsWithPrimary() throws Exception {
+		load(QuartzMultipleExecutorsWithPrimaryConfiguration.class);
+		assertThat(this.context.getBeansOfType(Executor.class)).hasSize(2);
+		assertThat(this.context.getBeansOfType(Scheduler.class)).hasSize(1);
+		Scheduler scheduler = this.context.getBean(Scheduler.class);
+		assertThat(scheduler.getMetaData().getThreadPoolClass())
+				.isEqualTo(LocalTaskExecutorThreadPool.class);
+	}
+
+	@Test
+	public void withMultipleTaskExecutorsWithCustomizer() throws Exception {
+		load(QuartzMultipleExecutorsWithCustomizerConfiguration.class);
+		assertThat(this.context.getBeansOfType(Executor.class)).hasSize(3);
+		assertThat(this.context.getBeansOfType(Scheduler.class)).hasSize(1);
+		Scheduler scheduler = this.context.getBean(Scheduler.class);
+		assertThat(scheduler.getMetaData().getThreadPoolClass())
+				.isEqualTo(LocalTaskExecutorThreadPool.class);
+	}
+
 	@Test
 	public void withConfiguredJobAndTrigger() throws Exception {
 		load(QuartzFullConfiguration.class, "test-name=withConfiguredJobAndTrigger");
@@ -269,6 +301,46 @@ public class QuartzAutoConfigurationTests {
 
 	}
 
+	@Configuration
+	protected static class QuartzMultipleExecutorsConfiguration
+			extends QuartzExecutorConfiguration {
+
+		@Bean
+		public Executor anotherExecutor() {
+			return Executors.newSingleThreadExecutor();
+		}
+
+	}
+
+	@Configuration
+	protected static class QuartzMultipleExecutorsWithPrimaryConfiguration
+			extends QuartzExecutorConfiguration {
+
+		@Bean
+		@Primary
+		public Executor primaryExecutor() {
+			return Executors.newSingleThreadExecutor();
+		}
+
+	}
+
+	@Configuration
+	protected static class QuartzMultipleExecutorsWithCustomizerConfiguration
+			extends QuartzMultipleExecutorsConfiguration {
+
+		@Bean
+		public Executor yetAnotherExecutor() {
+			return Executors.newSingleThreadExecutor();
+		}
+
+		@Bean
+		public SchedulerFactoryBeanCustomizer customizer() {
+			return schedulerFactoryBean -> schedulerFactoryBean
+					.setTaskExecutor(yetAnotherExecutor());
+		}
+
+	}
+
 	@Configuration
 	protected static class QuartzCustomConfiguration extends BaseQuartzConfiguration {