Only auto-configure LogbackMetrics when Logback is actually being used

Closes gh-12286

spring-boot-project/spring-boot-actuator-autoconfigure/pom.xml

@@ -37,6 +37,11 @@
 			<artifactId>spring-context</artifactId>
 		</dependency>
 		<!-- Optional -->
+		<dependency>
+			<groupId>ch.qos.logback</groupId>
+			<artifactId>logback-classic</artifactId>
+			<optional>true</optional>
+		</dependency>
 		<dependency>
 			<groupId>com.fasterxml.jackson.dataformat</groupId>
 			<artifactId>jackson-dataformat-xml</artifactId>
@@ -379,11 +384,6 @@
 			<artifactId>spring-boot-test-support</artifactId>
 			<scope>test</scope>
 		</dependency>
-		<dependency>
-			<groupId>ch.qos.logback</groupId>
-			<artifactId>logback-classic</artifactId>
-			<scope>test</scope>
-		</dependency>
 		<dependency>
 			<groupId>io.projectreactor</groupId>
 			<artifactId>reactor-test</artifactId>

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/MetricsAutoConfiguration.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.actuate.autoconfigure.metrics;
 
+import ch.qos.logback.classic.LoggerContext;
 import io.micrometer.core.annotation.Timed;
 import io.micrometer.core.instrument.Clock;
 import io.micrometer.core.instrument.binder.jvm.ClassLoaderMetrics;
@@ -26,17 +27,25 @@ import io.micrometer.core.instrument.binder.logging.LogbackMetrics;
 import io.micrometer.core.instrument.binder.system.FileDescriptorMetrics;
 import io.micrometer.core.instrument.binder.system.ProcessorMetrics;
 import io.micrometer.core.instrument.binder.system.UptimeMetrics;
+import org.slf4j.ILoggerFactory;
+import org.slf4j.LoggerFactory;
 
 import org.springframework.boot.autoconfigure.AutoConfigureBefore;
 import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
+import org.springframework.boot.autoconfigure.condition.ConditionMessage;
+import org.springframework.boot.autoconfigure.condition.ConditionOutcome;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
+import org.springframework.boot.autoconfigure.condition.SpringBootCondition;
 import org.springframework.boot.context.properties.EnableConfigurationProperties;
 import org.springframework.context.ApplicationContext;
 import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.ConditionContext;
+import org.springframework.context.annotation.Conditional;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.annotation.Order;
+import org.springframework.core.type.AnnotatedTypeMetadata;
 
 /**
  * {@link EnableAutoConfiguration Auto-configuration} for Micrometer-based metrics.
@@ -103,7 +112,9 @@ public class MetricsAutoConfiguration {
 	static class MeterBindersConfiguration {
 
 		@Bean
-		@ConditionalOnClass(name = "ch.qos.logback.classic.Logger")
+		@ConditionalOnClass(name = { "ch.qos.logback.classic.LoggerContext",
+				"org.slf4j.LoggerFactory" })
+		@Conditional(LogbackLoggingCondition.class)
 		@ConditionalOnMissingBean(LogbackMetrics.class)
 		@ConditionalOnProperty(value = "management.metrics.binders.logback.enabled", matchIfMissing = true)
 		public LogbackMetrics logbackMetrics() {
@@ -133,4 +144,23 @@ public class MetricsAutoConfiguration {
 
 	}
 
+	static class LogbackLoggingCondition extends SpringBootCondition {
+
+		@Override
+		public ConditionOutcome getMatchOutcome(ConditionContext context,
+				AnnotatedTypeMetadata metadata) {
+			ILoggerFactory loggerFactory = LoggerFactory.getILoggerFactory();
+			ConditionMessage.Builder message = ConditionMessage
+					.forCondition("LogbackLoggingCondition");
+			if (loggerFactory instanceof LoggerContext) {
+				return ConditionOutcome.match(
+						message.because("ILoggerFactory is a Logback LoggerContext"));
+			}
+			return ConditionOutcome
+					.noMatch(message.because("ILoggerFactory is an instance of "
+							+ loggerFactory.getClass().getCanonicalName()));
+		}
+
+	}
+
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/MetricsAutoConfigurationWithLog4j2AndLogbackTests.java

@@ -0,0 +1,58 @@
+/*
+ * Copyright 2012-2018 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.actuate.autoconfigure.metrics;
+
+import io.micrometer.core.instrument.binder.logging.LogbackMetrics;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.autoconfigure.condition.ConditionEvaluationReport;
+import org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportMessage;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.boot.testsupport.runner.classpath.ClassPathOverrides;
+import org.springframework.boot.testsupport.runner.classpath.ModifiedClassPathRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link MetricsAutoConfiguration} when both Log4j2 and Logback are on the
+ * classpath.
+ *
+ * @author Andy Wilkinson
+ */
+@RunWith(ModifiedClassPathRunner.class)
+@ClassPathOverrides({ "org.apache.logging.log4j:log4j-core:2.9.0",
+		"org.apache.logging.log4j:log4j-slf4j-impl:2.9.0" })
+public class MetricsAutoConfigurationWithLog4j2AndLogbackTests {
+
+	private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
+			.withConfiguration(AutoConfigurations.of(MetricsAutoConfiguration.class));
+
+	@Test
+	public void doesNotConfigureLogbackMetrics() {
+		this.contextRunner.run((context) -> {
+			System.out.println(
+					new ConditionEvaluationReportMessage(ConditionEvaluationReport
+							.get((ConfigurableListableBeanFactory) context
+									.getAutowireCapableBeanFactory())));
+			assertThat(context).doesNotHaveBean(LogbackMetrics.class);
+		});
+	}
+
+}