Merge pull request #12324 from Jon Schneider

* gh-12324:
  Polish "Improve docs on custom metrics"
  Improve docs on custom metrics

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

@@ -1749,9 +1749,18 @@ factories with a metric named `rabbitmq`.
 
 [[production-ready-metrics-custom]]
 === Registering custom metrics
-To register custom metrics, create a `MeterBinder` bean. By default, all `MeterBinder`
-beans will be automatically applied to the micrometer `MeterRegistry.Config`.
+To register custom metrics, inject `MeterRegistry` into your component, as shown in the
+following example:
+
+[source,java,indent=0]
+----
+include::{code-examples}/actuate/metrics/MetricsMeterRegistryInjectionExample.java[tag=component]
+----
 
+If you find that you repeatedly instrument a suite of metrics across components or
+applications, you may encapsulate this suite in a `MeterBinder` implementation. By
+default, metrics from all `MeterBinder` beans will be automatically bound to
+the Spring-managed `MeterRegistry`.
 
 
 [[production-ready-metrics-per-meter-properties]]

spring-boot-project/spring-boot-docs/src/main/java/org/springframework/boot/docs/actuate/metrics/MetricsMeterRegistryInjectionExample.java

+/*
+ * 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.docs.actuate.metrics;
+
+import java.util.List;
+import java.util.concurrent.CopyOnWriteArrayList;
+
+import io.micrometer.core.instrument.MeterRegistry;
+import io.micrometer.core.instrument.Tags;
+
+/**
+ * Example to show injection and use of a {@link MeterRegistry}.
+ *
+ * @author Andy Wilkinson
+ */
+public class MetricsMeterRegistryInjectionExample {
+
+	// tag::component[]
+	class Dictionary {
+
+		private final List<String> words = new CopyOnWriteArrayList<>();
+
+		Dictionary(MeterRegistry registry) {
+			registry.gaugeCollectionSize("dictionary.size", Tags.empty(), this.words);
+		}
+
+		// …
+
+	}
+	// end::component[]
+
+}