Auto-configure Micrometer's Log4j2 metrics

Closes gh-14524

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

@@ -198,6 +198,11 @@
 			<artifactId>commons-dbcp2</artifactId>
 			<optional>true</optional>
 		</dependency>
+		<dependency>
+			<groupId>org.apache.logging.log4j</groupId>
+			<artifactId>log4j-core</artifactId>
+			<optional>true</optional>
+		</dependency>
 		<dependency>
 			<groupId>org.apache.tomcat.embed</groupId>
 			<artifactId>tomcat-embed-core</artifactId>

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/Log4J2MetricsAutoConfiguration.java

@@ -0,0 +1,48 @@
+/*
+ * 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.MeterRegistry;
+import io.micrometer.core.instrument.binder.logging.Log4j2Metrics;
+import org.apache.logging.log4j.core.LoggerContext;
+
+import org.springframework.boot.autoconfigure.AutoConfigureAfter;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnBean;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+/**
+ * Auto-configuration for Log4J2 metrics.
+ *
+ * @author Andy Wilkinson
+ * @since 2.1.0
+ */
+@Configuration
+@AutoConfigureAfter(MetricsAutoConfiguration.class)
+@ConditionalOnClass({ Log4j2Metrics.class, LoggerContext.class })
+@ConditionalOnBean(MeterRegistry.class)
+public class Log4J2MetricsAutoConfiguration {
+
+	@Bean
+	@ConditionalOnMissingBean
+	public Log4j2Metrics log4j2Metrics() {
+		return new Log4j2Metrics();
+	}
+
+}

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/resources/META-INF/spring.factories

@@ -35,6 +35,7 @@ org.springframework.boot.actuate.autoconfigure.management.HeapDumpWebEndpointAut
 org.springframework.boot.actuate.autoconfigure.management.ThreadDumpEndpointAutoConfiguration,\
 org.springframework.boot.actuate.autoconfigure.metrics.CompositeMeterRegistryAutoConfiguration,\
 org.springframework.boot.actuate.autoconfigure.metrics.JvmMetricsAutoConfiguration,\
+org.springframework.boot.actuate.autoconfigure.metrics.Log4J2MetricsAutoConfiguration,\
 org.springframework.boot.actuate.autoconfigure.metrics.LogbackMetricsAutoConfiguration,\
 org.springframework.boot.actuate.autoconfigure.metrics.MetricsAutoConfiguration,\
 org.springframework.boot.actuate.autoconfigure.metrics.MetricsEndpointAutoConfiguration,\

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/Log4J2MetricsAutoConfigurationTests.java

@@ -0,0 +1,64 @@
+/*
+ * 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.Log4j2Metrics;
+import org.junit.Test;
+
+import org.springframework.boot.actuate.autoconfigure.metrics.test.MetricsRun;
+import org.springframework.boot.autoconfigure.AutoConfigurations;
+import org.springframework.boot.test.context.runner.ApplicationContextRunner;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link Log4J2MetricsAutoConfiguration}.
+ *
+ * @author Andy Wilkinson
+ */
+public class Log4J2MetricsAutoConfigurationTests {
+
+	private final ApplicationContextRunner contextRunner = new ApplicationContextRunner()
+			.with(MetricsRun.simple()).withConfiguration(
+					AutoConfigurations.of(Log4J2MetricsAutoConfiguration.class));
+
+	@Test
+	public void autoConfiguresLog4J2Metrics() {
+		this.contextRunner
+				.run((context) -> assertThat(context).hasSingleBean(Log4j2Metrics.class));
+	}
+
+	@Test
+	public void allowsCustomLog4J2MetricsToBeUsed() {
+		this.contextRunner.withUserConfiguration(CustomLog4J2MetricsConfiguration.class)
+				.run((context) -> assertThat(context).hasSingleBean(Log4j2Metrics.class)
+						.hasBean("customLog4J2Metrics"));
+	}
+
+	@Configuration
+	static class CustomLog4J2MetricsConfiguration {
+
+		@Bean
+		public Log4j2Metrics customLog4J2Metrics() {
+			return new Log4j2Metrics();
+		}
+
+	}
+
+}

spring-boot-project/spring-boot-docs/src/main/asciidoc/production-ready-features.adoc

@@ -1707,6 +1707,7 @@ Spring Boot registers the following core metrics when applicable:
 ** Number of classes loaded/unloaded
 * CPU metrics
 * File descriptor metrics
+* Log4j2 metrics: record the number of events logged to Log4j2 at each level
 * Logback metrics: record the number of events logged to Logback at each level
 * Uptime metrics: report a gauge for uptime and a fixed gauge representing the
 application's absolute start time