GH-3396: Add Docs for Micrometer MeterFilters

Resolves https://github.com/spring-projects/spring-integration/issues/3396

* Add an example.

spring-integration-core/src/test/java/org/springframework/integration/support/management/micrometer/MicrometerMetricsTests.java

@@ -59,6 +59,7 @@ import org.springframework.test.context.junit.jupiter.SpringJUnitConfig;
 import org.springframework.test.context.support.DependencyInjectionTestExecutionListener;
 
 import io.micrometer.core.instrument.MeterRegistry;
+import io.micrometer.core.instrument.config.MeterFilter;
 import io.micrometer.core.instrument.search.MeterNotFoundException;
 import io.micrometer.core.instrument.simple.SimpleMeterRegistry;
 
@@ -92,6 +93,9 @@ public class MicrometerMetricsTests {
 	@Autowired
 	private QueueChannel queue;
 
+	@Autowired
+	private QueueChannel noMeters;
+
 	@Autowired
 	private PollableChannel badPoll;
 
@@ -131,7 +135,7 @@ public class MicrometerMetricsTests {
 
 		nullChannel.send(message);
 		MeterRegistry registry = this.meterRegistry;
-		assertThat(registry.get("spring.integration.channels").gauge().value()).isEqualTo(7);
+		assertThat(registry.get("spring.integration.channels").gauge().value()).isEqualTo(8);
 		assertThat(registry.get("spring.integration.handlers").gauge().value()).isEqualTo(4);
 		assertThat(registry.get("spring.integration.sources").gauge().value()).isEqualTo(1);
 
@@ -243,6 +247,13 @@ public class MicrometerMetricsTests {
 				.tag("result", "success")
 				.timer().count()).isEqualTo(2);
 
+		this.noMeters.send(message);
+		assertThatExceptionOfType(MeterNotFoundException.class).isThrownBy(() -> registry.get("spring.integration.send")
+				.tag("type", "channel")
+				.tag("name", "noMeters")
+				.tag("result", "success")
+				.timer().count());
+
 		this.context.close();
 
 		assertThatExceptionOfType(MeterNotFoundException.class)
@@ -264,7 +275,11 @@ public class MicrometerMetricsTests {
 
 		@Bean
 		public static MeterRegistry meterRegistry() {
-			return new SimpleMeterRegistry();
+			SimpleMeterRegistry registry = new SimpleMeterRegistry();
+			registry.config().meterFilter(MeterFilter.deny(id ->
+					"channel".equals(id.getTag("type")) &&
+					"noMeters".equals(id.getTag("name"))));
+			return registry;
 		}
 
 		@ServiceActivator(inputChannel = "channel")
@@ -310,6 +325,11 @@ public class MicrometerMetricsTests {
 			return new QueueChannel(10);
 		}
 
+		@Bean
+		public QueueChannel noMeters() {
+			return new QueueChannel(10);
+		}
+
 		@Bean
 		public PollableChannel badPoll() {
 			return new AbstractPollableChannel() {

src/reference/asciidoc/metrics.adoc

@@ -4,7 +4,7 @@
 This section describes how to capture metrics for Spring Integration.
 In recent versions, we have relied more on Micrometer (see https://micrometer.io), and we plan to use Micrometer even more in future releases.
 
-[[configuring-metrics-capture]]
+[[legacy-metrics]]
 ==== Legacy Metrics
 
 Legacy metrics were removed in Version 5.4; see Micrometer Integration below.
@@ -48,6 +48,8 @@ IMPORTANT: `defaultLoggingEnabled` is applied only if you have not explicitly co
 [[micrometer-integration]]
 ==== Micrometer Integration
 
+===== Overview
+
 Starting with version 5.0.3, the presence of a https://micrometer.io/[Micrometer] `MeterRegistry` in the application context triggers support for Micrometer metrics.
 
 To use Micrometer, add one of the `MeterRegistry` beans to the application context.
@@ -118,3 +120,34 @@ and
 * `tag`: `type:channel`
 * `tag`: `name:<componentName>`
 * `description`: `The remaining capacity of the queue channel`
+
+===== Disabling Meters
+
+With the <<legacy-metrics>> (which have now been removed), you could specify which integration components would collect metrics.
+By default, all meters are registered when first used.
+Now, with Micrometer, you can add `MeterFilter` s to the `MeterRegistry` to prevent some or all from being registered.
+You can filter out (deny) meters by any of the properties provided, `name`, `tag`, etc.
+See https://micrometer.io/docs/concepts#_meter_filters[Meter Filters] in the Micrometer documentation for more information.
+
+For example, given:
+
+====
+[source, java]
+----
+@Bean
+public QueueChannel noMeters() {
+    return new QueueChannel(10);
+}
+----
+====
+
+You can suppress registration of meters for just this channel with:
+
+====
+[source, java]
+----
+registry.config().meterFilter(MeterFilter.deny(id ->
+        "channel".equals(id.getTag("type")) &&
+        "noMeters".equals(id.getTag("name"))));
+----
+====