Flexible registration of additional PublicMetrics

This commit permits the use of several PublicMetrics instances by
default. Previously, only one PublicMetrics service could be specified
and a user configuration would remove all the defaulting.

VanillaPublicMetrics now takes a collection of PublicMetrics and
invokes them in sequence to build the final collection of metrics.
The system-related metrics have been moved to SystemPublicMetrics and
are registered by default.

Also updated the documentation to mention this feature and how it
could be fully overridden.

Fixes gh-1094

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/autoconfigure/EndpointAutoConfiguration.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.actuate.autoconfigure;
 
+import java.util.Collection;
 import java.util.HashMap;
 import java.util.LinkedHashMap;
 import java.util.Map;
@@ -35,6 +36,7 @@ import org.springframework.boot.actuate.endpoint.MetricsEndpoint;
 import org.springframework.boot.actuate.endpoint.PublicMetrics;
 import org.springframework.boot.actuate.endpoint.RequestMappingEndpoint;
 import org.springframework.boot.actuate.endpoint.ShutdownEndpoint;
+import org.springframework.boot.actuate.endpoint.SystemPublicMetrics;
 import org.springframework.boot.actuate.endpoint.TraceEndpoint;
 import org.springframework.boot.actuate.endpoint.VanillaPublicMetrics;
 import org.springframework.boot.actuate.health.HealthAggregator;
@@ -68,6 +70,7 @@ import org.springframework.web.servlet.handler.AbstractHandlerMethodMapping;
  * @author Phillip Webb
  * @author Greg Turnquist
  * @author Christian Dupuis
+ * @author Stephane Nicoll
  */
 @Configuration
 public class EndpointAutoConfiguration {
@@ -85,7 +88,7 @@ public class EndpointAutoConfiguration {
 	private MetricReader metricRepository = new InMemoryMetricRepository();
 
 	@Autowired(required = false)
-	private PublicMetrics metrics;
+	private Collection<PublicMetrics> allMetrics;
 
 	@Autowired(required = false)
 	private TraceRepository traceRepository = new InMemoryTraceRepository();
@@ -126,10 +129,8 @@ public class EndpointAutoConfiguration {
 	@Bean
 	@ConditionalOnMissingBean
 	public MetricsEndpoint metricsEndpoint() {
-		if (this.metrics == null) {
-			this.metrics = new VanillaPublicMetrics(this.metricRepository);
-		}
-		return new MetricsEndpoint(this.metrics);
+		PublicMetrics metrics = new VanillaPublicMetrics(this.metricRepository, this.allMetrics);
+		return new MetricsEndpoint(metrics);
 	}
 
 	@Bean
@@ -178,6 +179,16 @@ public class EndpointAutoConfiguration {
 		return endpoint;
 	}
 
+	@Configuration
+	protected static class CorePublicMetrics {
+
+		@Bean
+		SystemPublicMetrics systemPublicMetrics() {
+			return new SystemPublicMetrics();
+		}
+
+	}
+
 	@Configuration
 	protected static class InfoPropertiesConfiguration {
 

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/PublicMetrics.java

@@ -25,6 +25,7 @@ import org.springframework.boot.actuate.metrics.Metric;
  *
  * @author Dave Syer
  * @see VanillaPublicMetrics
+ * @see SystemPublicMetrics
  */
 public interface PublicMetrics {
 

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/SystemPublicMetrics.java

@@ -0,0 +1,136 @@
+/*
+ * Copyright 2012-2014 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.endpoint;
+
+import java.lang.management.ClassLoadingMXBean;
+import java.lang.management.GarbageCollectorMXBean;
+import java.lang.management.ManagementFactory;
+import java.lang.management.MemoryUsage;
+import java.lang.management.ThreadMXBean;
+import java.util.Collection;
+import java.util.LinkedHashSet;
+import java.util.List;
+
+import org.springframework.boot.actuate.metrics.Metric;
+import org.springframework.util.StringUtils;
+
+/**
+ * A {@link PublicMetrics} implementation that provides various
+ * system-related metrics.
+ *
+ * @author Dave Syer
+ * @author Stephane Nicoll
+ * @since 1.2.0
+ */
+public class SystemPublicMetrics implements PublicMetrics {
+
+	private long timestamp;
+
+	public SystemPublicMetrics() {
+		this.timestamp = System.currentTimeMillis();
+	}
+
+	@Override
+	public Collection<Metric<?>> metrics() {
+		Collection<Metric<?>> result = new LinkedHashSet<Metric<?>>();
+
+		addBasicMetrics(result);
+		addHeapMetrics(result);
+		addThreadMetrics(result);
+		addClassLoadingMetrics(result);
+		addGarbageCollectionMetrics(result);
+
+		return result;
+	}
+
+
+	/**
+	 * Add basic system metrics.
+	 */
+	protected void addBasicMetrics(Collection<Metric<?>> result) {
+		result.add(new Metric<Long>("mem",
+				Runtime.getRuntime().totalMemory() / 1024));
+		result.add(new Metric<Long>("mem.free", Runtime.getRuntime()
+				.freeMemory() / 1024));
+		result.add(new Metric<Integer>("processors", Runtime.getRuntime()
+				.availableProcessors()));
+		// Add JVM up time in ms
+		result.add(new Metric<Long>("uptime", ManagementFactory
+				.getRuntimeMXBean().getUptime()));
+		result.add(new Metric<Long>("instance.uptime", System.currentTimeMillis()
+				- this.timestamp));
+	}
+
+	/**
+	 * Add JVM heap metrics.
+	 */
+	protected void addHeapMetrics(Collection<Metric<?>> result) {
+		MemoryUsage memoryUsage = ManagementFactory.getMemoryMXBean()
+				.getHeapMemoryUsage();
+		result.add(new Metric<Long>("heap.committed", memoryUsage.getCommitted() / 1024));
+		result.add(new Metric<Long>("heap.init", memoryUsage.getInit() / 1024));
+		result.add(new Metric<Long>("heap.used", memoryUsage.getUsed() / 1024));
+		result.add(new Metric<Long>("heap", memoryUsage.getMax() / 1024));
+	}
+
+	/**
+	 * Add thread metrics.
+	 */
+	protected void addThreadMetrics(Collection<Metric<?>> result) {
+		ThreadMXBean threadMxBean = ManagementFactory.getThreadMXBean();
+		result.add(new Metric<Long>("threads.peak", (long) threadMxBean
+				.getPeakThreadCount()));
+		result.add(new Metric<Long>("threads.daemon", (long) threadMxBean
+				.getDaemonThreadCount()));
+		result.add(new Metric<Long>("threads", (long) threadMxBean.getThreadCount()));
+	}
+
+	/**
+	 * Add class loading metrics.
+	 */
+	protected void addClassLoadingMetrics(Collection<Metric<?>> result) {
+		ClassLoadingMXBean classLoadingMxBean = ManagementFactory.getClassLoadingMXBean();
+		result.add(new Metric<Long>("classes", (long) classLoadingMxBean
+				.getLoadedClassCount()));
+		result.add(new Metric<Long>("classes.loaded", classLoadingMxBean
+				.getTotalLoadedClassCount()));
+		result.add(new Metric<Long>("classes.unloaded", classLoadingMxBean
+				.getUnloadedClassCount()));
+	}
+
+	/**
+	 * Add garbage collection metrics.
+	 */
+	protected void addGarbageCollectionMetrics(Collection<Metric<?>> result) {
+		List<GarbageCollectorMXBean> garbageCollectorMxBeans = ManagementFactory
+				.getGarbageCollectorMXBeans();
+		for (GarbageCollectorMXBean garbageCollectorMXBean : garbageCollectorMxBeans) {
+			String name = beautifyGcName(garbageCollectorMXBean.getName());
+			result.add(new Metric<Long>("gc." + name + ".count", garbageCollectorMXBean.getCollectionCount()));
+			result.add(new Metric<Long>("gc." + name + ".time", garbageCollectorMXBean.getCollectionTime()));
+		}
+	}
+
+	/**
+	 * Turn GC names like 'PS Scavenge' or 'PS MarkSweep' into something that is more
+	 * metrics friendly.
+	 */
+	private String beautifyGcName(String name) {
+		return StringUtils.replace(name, " ", "_").toLowerCase();
+	}
+
+}

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/VanillaPublicMetrics.java

@@ -16,36 +16,37 @@
 
 package org.springframework.boot.actuate.endpoint;
 
-import java.lang.management.ClassLoadingMXBean;
-import java.lang.management.GarbageCollectorMXBean;
-import java.lang.management.ManagementFactory;
-import java.lang.management.MemoryUsage;
-import java.lang.management.ThreadMXBean;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.LinkedHashSet;
-import java.util.List;
 
 import org.springframework.boot.actuate.metrics.Metric;
 import org.springframework.boot.actuate.metrics.reader.MetricReader;
 import org.springframework.util.Assert;
-import org.springframework.util.StringUtils;
 
 /**
  * Default implementation of {@link PublicMetrics} that exposes all metrics from a
- * {@link MetricReader} along with memory information.
+ * {@link MetricReader} along with a collection of configurable {@link PublicMetrics}
+ * instances.
  *
  * @author Dave Syer
  * @author Christian Dupuis
+ * @author Stephane Nicoll
  */
 public class VanillaPublicMetrics implements PublicMetrics {
 
 	private final MetricReader reader;
-	private long timestamp;
+	private final Collection<PublicMetrics> publicMetrics;
 
-	public VanillaPublicMetrics(MetricReader reader) {
+	public VanillaPublicMetrics(MetricReader reader, Collection<PublicMetrics> publicMetrics) {
 		Assert.notNull(reader, "MetricReader must not be null");
+		Assert.notNull(publicMetrics, "PublicMetrics must not be null");
 		this.reader = reader;
-		this.timestamp = System.currentTimeMillis();
+		this.publicMetrics = publicMetrics;
+	}
+
+	public VanillaPublicMetrics(MetricReader reader) {
+		this(reader, Collections.<PublicMetrics>emptyList());
 	}
 
 	@Override
@@ -54,92 +55,11 @@ public class VanillaPublicMetrics implements PublicMetrics {
 		for (Metric<?> metric : this.reader.findAll()) {
 			result.add(metric);
 		}
-
-		addMetrics(result);
-		addHeapMetrics(result);
-		addThreadMetrics(result);
-		addClassLoadingMetrics(result);
-		addGarbageCollecitonMetrics(result);
-
-		return result;
-	}
-
-	/**
-	 * Add basic system metrics.
-	 */
-	protected void addMetrics(Collection<Metric<?>> result) {
-		result.add(new Metric<Long>("mem",
-				new Long(Runtime.getRuntime().totalMemory()) / 1024));
-		result.add(new Metric<Long>("mem.free", new Long(Runtime.getRuntime()
-				.freeMemory()) / 1024));
-		result.add(new Metric<Integer>("processors", Runtime.getRuntime()
-				.availableProcessors()));
-		// Add JVM uptime in ms
-		result.add(new Metric<Long>("uptime", new Long(ManagementFactory
-				.getRuntimeMXBean().getUptime())));
-		result.add(new Metric<Long>("instance.uptime", System.currentTimeMillis()
-				- this.timestamp));
-	}
-
-	/**
-	 * Add JVM heap metrics.
-	 */
-	protected void addHeapMetrics(Collection<Metric<?>> result) {
-		MemoryUsage memoryUsage = ManagementFactory.getMemoryMXBean()
-				.getHeapMemoryUsage();
-		result.add(new Metric<Long>("heap.committed", memoryUsage.getCommitted() / 1024));
-		result.add(new Metric<Long>("heap.init", memoryUsage.getInit() / 1024));
-		result.add(new Metric<Long>("heap.used", memoryUsage.getUsed() / 1024));
-		result.add(new Metric<Long>("heap", memoryUsage.getMax() / 1024));
-	}
-
-	/**
-	 * Add thread metrics.
-	 */
-	protected void addThreadMetrics(Collection<Metric<?>> result) {
-		ThreadMXBean threadMxBean = ManagementFactory.getThreadMXBean();
-		result.add(new Metric<Long>("threads.peak", new Long(threadMxBean
-				.getPeakThreadCount())));
-		result.add(new Metric<Long>("threads.daemon", new Long(threadMxBean
-				.getDaemonThreadCount())));
-		result.add(new Metric<Long>("threads", new Long(threadMxBean.getThreadCount())));
-	}
-
-	/**
-	 * Add class loading metrics.
-	 */
-	protected void addClassLoadingMetrics(Collection<Metric<?>> result) {
-		ClassLoadingMXBean classLoadingMxBean = ManagementFactory.getClassLoadingMXBean();
-		result.add(new Metric<Long>("classes", new Long(classLoadingMxBean
-				.getLoadedClassCount())));
-		result.add(new Metric<Long>("classes.loaded", new Long(classLoadingMxBean
-				.getTotalLoadedClassCount())));
-		result.add(new Metric<Long>("classes.unloaded", new Long(classLoadingMxBean
-				.getUnloadedClassCount())));
+		for (PublicMetrics publicMetric : publicMetrics) {
+			result.addAll(publicMetric.metrics());
 		}
 
-	/**
-	 * Add garbage collection metrics.
-	 */
-	protected void addGarbageCollecitonMetrics(Collection<Metric<?>> result) {
-		List<GarbageCollectorMXBean> garbageCollectorMxBeans = ManagementFactory
-				.getGarbageCollectorMXBeans();
-		for (int i = 0; i < garbageCollectorMxBeans.size(); i++) {
-			GarbageCollectorMXBean garbageCollectorMXBean = garbageCollectorMxBeans
-					.get(i);
-			String name = beautifyGcName(garbageCollectorMXBean.getName());
-			result.add(new Metric<Long>("gc." + name + ".count", new Long(
-					garbageCollectorMXBean.getCollectionCount())));
-			result.add(new Metric<Long>("gc." + name + ".time", new Long(
-					garbageCollectorMXBean.getCollectionTime())));
-		}
+		return result;
 	}
 
-	/**
-	 * Turn GC names like 'PS Scavenge' or 'PS MarkSweep' into something that is more
-	 * metrics friendly.
-	 */
-	private String beautifyGcName(String name) {
-		return StringUtils.replace(name, " ", "_").toLowerCase();
-	}
 }

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/autoconfigure/EndpointAutoConfigurationTests.java

@@ -17,7 +17,6 @@
 package org.springframework.boot.actuate.autoconfigure;
 
 import org.junit.After;
-import org.junit.Before;
 import org.junit.Test;
 import org.springframework.boot.actuate.endpoint.AutoConfigurationReportEndpoint;
 import org.springframework.boot.actuate.endpoint.BeansEndpoint;
@@ -26,20 +25,28 @@ import org.springframework.boot.actuate.endpoint.EnvironmentEndpoint;
 import org.springframework.boot.actuate.endpoint.HealthEndpoint;
 import org.springframework.boot.actuate.endpoint.InfoEndpoint;
 import org.springframework.boot.actuate.endpoint.MetricsEndpoint;
+import org.springframework.boot.actuate.endpoint.PublicMetrics;
 import org.springframework.boot.actuate.endpoint.RequestMappingEndpoint;
 import org.springframework.boot.actuate.endpoint.ShutdownEndpoint;
 import org.springframework.boot.actuate.endpoint.TraceEndpoint;
 import org.springframework.boot.actuate.health.Health;
+import org.springframework.boot.actuate.metrics.Metric;
 import org.springframework.boot.autoconfigure.condition.ConditionEvaluationReport;
 import org.springframework.boot.autoconfigure.jdbc.EmbeddedDataSourceConfiguration;
 import org.springframework.boot.test.EnvironmentTestUtils;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Map;
+
 /**
  * Tests for {@link EndpointAutoConfiguration}.
  *
@@ -47,18 +54,12 @@ import static org.junit.Assert.assertTrue;
  * @author Phillip Webb
  * @author Greg Turnquist
  * @author Christian Dupuis
+ * @author Stephane Nicoll
  */
 public class EndpointAutoConfigurationTests {
 
 	private AnnotationConfigApplicationContext context;
 
-	@Before
-	public void setup() {
-		this.context = new AnnotationConfigApplicationContext();
-		this.context.register(EndpointAutoConfiguration.class);
-		this.context.refresh();
-	}
-
 	@After
 	public void close() {
 		if (this.context != null) {
@@ -68,6 +69,7 @@ public class EndpointAutoConfigurationTests {
 
 	@Test
 	public void endpoints() throws Exception {
+		load(EndpointAutoConfiguration.class);
 		assertNotNull(this.context.getBean(BeansEndpoint.class));
 		assertNotNull(this.context.getBean(DumpEndpoint.class));
 		assertNotNull(this.context.getBean(EnvironmentEndpoint.class));
@@ -81,10 +83,8 @@ public class EndpointAutoConfigurationTests {
 
 	@Test
 	public void healthEndpoint() {
-		this.context = new AnnotationConfigApplicationContext();
-		this.context.register(EmbeddedDataSourceConfiguration.class,
+		load(EmbeddedDataSourceConfiguration.class,
 				EndpointAutoConfiguration.class, HealthIndicatorAutoConfiguration.class);
-		this.context.refresh();
 		HealthEndpoint bean = this.context.getBean(HealthEndpoint.class);
 		assertNotNull(bean);
 		Health result = bean.invoke();
@@ -94,10 +94,8 @@ public class EndpointAutoConfigurationTests {
 
 	@Test
 	public void healthEndpointWithDefaultHealthIndicator() {
-		this.context = new AnnotationConfigApplicationContext();
-		this.context.register(EndpointAutoConfiguration.class,
+		load(EndpointAutoConfiguration.class,
 				HealthIndicatorAutoConfiguration.class);
-		this.context.refresh();
 		HealthEndpoint bean = this.context.getBean(HealthEndpoint.class);
 		assertNotNull(bean);
 		Health result = bean.invoke();
@@ -105,11 +103,33 @@ public class EndpointAutoConfigurationTests {
 	}
 
 	@Test
-	public void autoconfigurationAuditEndpoints() {
-		this.context = new AnnotationConfigApplicationContext();
-		this.context.register(EndpointAutoConfiguration.class,
+	public void metricEndpointsHasSystemMetricsByDefault() {
+		load(EndpointAutoConfiguration.class);
+		MetricsEndpoint endpoint = this.context.getBean(MetricsEndpoint.class);
+		Map<String, Object> metrics = endpoint.invoke();
+		assertTrue(metrics.containsKey("mem"));
+		assertTrue(metrics.containsKey("heap.used"));
+	}
+
+	@Test
+	public void metricEndpointCustomPublicMetrics() {
+		load(CustomPublicMetricsConfig.class, EndpointAutoConfiguration.class);
+		MetricsEndpoint endpoint = this.context.getBean(MetricsEndpoint.class);
+		Map<String, Object> metrics = endpoint.invoke();
+
+		// Custom metrics
+		assertTrue(metrics.containsKey("foo"));
+
+		// System metrics still available
+		assertTrue(metrics.containsKey("mem"));
+		assertTrue(metrics.containsKey("heap.used"));
+
+	}
+
+	@Test
+	public void autoConfigurationAuditEndpoints() {
+		load(EndpointAutoConfiguration.class,
 				ConditionEvaluationReport.class);
-		this.context.refresh();
 		assertNotNull(this.context.getBean(AutoConfigurationReportEndpoint.class));
 	}
 
@@ -136,4 +156,25 @@ public class EndpointAutoConfigurationTests {
 		assertNotNull(endpoint);
 		assertNull(endpoint.invoke().get("git"));
 	}
+
+	private void load(Class<?>... config) {
+		this.context = new AnnotationConfigApplicationContext();
+		this.context.register(config);
+		this.context.refresh();
+	}
+
+
+	@Configuration
+	static class CustomPublicMetricsConfig {
+
+		@Bean
+		PublicMetrics customPublicMetrics() {
+			return new PublicMetrics() {
+				@Override
+				public Collection<Metric<?>> metrics() {
+					return Collections.<Metric<?>>singleton(new Metric<Integer>("foo", 1));
+				}
+			};
+		}
+	}
 }

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/SystemPublicMetricsTests.java

@@ -0,0 +1,61 @@
+/*
+ * Copyright 2012-2014 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.endpoint;
+
+import static org.junit.Assert.*;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.junit.Test;
+
+import org.springframework.boot.actuate.metrics.Metric;
+
+/**
+ * Tests for {@link SystemPublicMetrics}
+ *
+ * @author Stephane Nicoll
+ */
+public class SystemPublicMetricsTests {
+
+	@Test
+	public void testSystemMetrics() throws Exception {
+		SystemPublicMetrics publicMetrics = new SystemPublicMetrics();
+		Map<String, Metric<?>> results = new HashMap<String, Metric<?>>();
+		for (Metric<?> metric : publicMetrics.metrics()) {
+			results.put(metric.getName(), metric);
+		}
+		assertTrue(results.containsKey("mem"));
+		assertTrue(results.containsKey("mem.free"));
+		assertTrue(results.containsKey("processors"));
+		assertTrue(results.containsKey("uptime"));
+
+		assertTrue(results.containsKey("heap.committed"));
+		assertTrue(results.containsKey("heap.init"));
+		assertTrue(results.containsKey("heap.used"));
+		assertTrue(results.containsKey("heap"));
+
+		assertTrue(results.containsKey("threads.peak"));
+		assertTrue(results.containsKey("threads.daemon"));
+		assertTrue(results.containsKey("threads"));
+
+		assertTrue(results.containsKey("classes.loaded"));
+		assertTrue(results.containsKey("classes.unloaded"));
+		assertTrue(results.containsKey("classes"));
+	}
+
+}

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/endpoint/VanillaPublicMetricsTests.java

@@ -16,8 +16,12 @@
 
 package org.springframework.boot.actuate.endpoint;
 
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
 import java.util.Date;
 import java.util.HashMap;
+import java.util.LinkedHashSet;
 import java.util.Map;
 
 import org.junit.Test;
@@ -25,14 +29,14 @@ import org.springframework.boot.actuate.metrics.Metric;
 import org.springframework.boot.actuate.metrics.repository.InMemoryMetricRepository;
 
 import static org.hamcrest.Matchers.equalTo;
-import static org.junit.Assert.assertThat;
-import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.*;
 
 /**
  * Tests for {@link VanillaPublicMetrics}.
  *
  * @author Phillip Webb
  * @author Christian Dupuis
+ * @author Stephane Nicoll
  */
 public class VanillaPublicMetricsTests {
 
@@ -45,36 +49,38 @@ public class VanillaPublicMetricsTests {
 		for (Metric<?> metric : publicMetrics.metrics()) {
 			results.put(metric.getName(), metric);
 		}
-		assertTrue(results.containsKey("mem"));
-		assertTrue(results.containsKey("mem.free"));
 		assertThat(results.get("a").getValue().doubleValue(), equalTo(0.5));
 	}
 
 	@Test
-	public void testSystemMetrics() throws Exception {
+	public void testAdditionalMetrics() throws Exception {
 		InMemoryMetricRepository repository = new InMemoryMetricRepository();
-		repository.set(new Metric<Double>("a", 0.5, new Date()));
-		VanillaPublicMetrics publicMetrics = new VanillaPublicMetrics(repository);
+		Collection<PublicMetrics> allMetrics = new ArrayList<PublicMetrics>();
+		allMetrics.add(new ImmutablePublicMetrics(new Metric<Number>("first", 2L)));
+		allMetrics.add(new ImmutablePublicMetrics(new Metric<Number>("second", 4L)));
+
+		VanillaPublicMetrics publicMetrics = new VanillaPublicMetrics(repository, allMetrics);
 		Map<String, Metric<?>> results = new HashMap<String, Metric<?>>();
 		for (Metric<?> metric : publicMetrics.metrics()) {
 			results.put(metric.getName(), metric);
 		}
-		assertTrue(results.containsKey("mem"));
-		assertTrue(results.containsKey("mem.free"));
-		assertTrue(results.containsKey("processors"));
-		assertTrue(results.containsKey("uptime"));
+		assertTrue(results.containsKey("first"));
+		assertTrue(results.containsKey("second"));
+		assertEquals(2, results.size());
+	}
 
-		assertTrue(results.containsKey("heap.committed"));
-		assertTrue(results.containsKey("heap.init"));
-		assertTrue(results.containsKey("heap.used"));
-		assertTrue(results.containsKey("heap"));
 
-		assertTrue(results.containsKey("threads.peak"));
-		assertTrue(results.containsKey("threads.daemon"));
-		assertTrue(results.containsKey("threads"));
+	private static class ImmutablePublicMetrics implements PublicMetrics {
+		private final Collection<Metric<?>> metrics;
 
-		assertTrue(results.containsKey("classes.loaded"));
-		assertTrue(results.containsKey("classes.unloaded"));
-		assertTrue(results.containsKey("classes"));
+		private ImmutablePublicMetrics(Metric<?> metrics) {
+			this.metrics = new LinkedHashSet<Metric<?>>();
+			this.metrics.addAll(Arrays.asList(metrics));
+		}
+
+		@Override
+		public Collection<Metric<?>> metrics() {
+			return metrics;
+		}
 	}
 }

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

@@ -583,8 +583,14 @@ documentation].
 == Metrics
 Spring Boot Actuator includes a metrics service with ``gauge'' and ``counter'' support.
 A ``gauge'' records a single value; and a ``counter'' records a delta (an increment or
-decrement). Metrics for all HTTP requests are automatically recorded, so if you hit the
-`metrics` endpoint should should see a response similar to this:
+decrement). Spring Boot Actuator also provides a
+{sc-spring-boot-actuator}/endpoint/PublicMetrics.{sc-ext}[`PublicMetrics`] interface that
+you can implement to expose metrics that you cannot record via one of those two mechanisms. Look
+at {sc-spring-boot-actuator}/endpoint/SystemPublicMetrics.{sc-ext}[`SystemPublicMetrics`]
+for an example.
+
+Metrics for all HTTP requests are automatically recorded, so if you hit the
+`metrics` endpoint you should see a response similar to this:
 
 [source,json,indent=0]
 ----
@@ -612,9 +618,10 @@ decrement). Metrics for all HTTP requests are automatically recorded, so if you
 ----
 
 Here we can see basic `memory`, `heap`, `class loading`, `processor` and `thread pool`
-information along with some HTTP metrics. In this instance the `root` (``/'') and `/metrics`
-URLs have returned `HTTP 200` responses `20` and `3` times respectively. It also appears
-that the `root` URL returned `HTTP 401` (unauthorized) `4` times.
+information provided by `SystemPublicMetrics` along with some HTTP metrics. In this
+instance the `root` (``/'') and `/metrics` URLs have returned `HTTP 200` responses `20`
+and `3` times respectively. It also appears that the `root` URL returned `HTTP 401`
+(unauthorized) `4` times.
 
 The `gauge` shows the last response time for a request. So the last request to `root` took
 `2ms` to respond and the last to `/metrics` took `3ms`.
@@ -661,6 +668,13 @@ TIP: You can use any string as a metric name but you should follow guidelines of
 store/graphing technology. Some good guidelines for Graphite are available on
 http://matt.aimonetti.net/posts/2013/06/26/practical-guide-to-graphite-monitoring/[Matt Aimonetti's Blog].
 
+[[production-ready-public-metrics]]
+=== Adding your own public metrics
+
+To add additional metrics that are computed every time the metrics endpoint is invoked,
+simply register additional `PublicMetrics` implementation bean(s). By default, all such
+beans are gathered by the endpoint. You can easily change that by defining your own
+`MetricsEndpoint`.
 
 
 [[production-ready-metric-repositories]]