Reference doc update for system

docs/modules/ROOT/nav.adoc

@@ -47,6 +47,7 @@
 ** xref:reference/mongodb.adoc[MongoDB]
 ** xref:reference/netty.adoc[Netty]
 ** xref:reference/okhttpclient.adoc[OkHttpClient]
+** xref:reference/system.adoc[System]
 * xref:guides.adoc[Guides]
 ** xref:guides/console-reporter.adoc[Passing through to Dropwizard's console reporter]
 ** xref:guides/http-sender-resilience4j-retry.adoc[HttpSender with Resilience4j retry]

docs/modules/ROOT/pages/reference/system.adoc

@@ -0,0 +1,48 @@
+[[overview]]
+= System Metrics
+
+Micrometer provides several binders for system monitoring:
+
+* <<system-disk, Disk Space Metrics>>
+* <<system-file, File Descriptor Metrics>>
+* <<system-processor, Processor Metrics>>
+* <<system-uptime, Uptime Metrics>>
+
+[[system-disk]]
+== System Disk Space Metrics
+
+[source,java,subs=+attributes]
+-----
+// Usage example
+include::{include-core-test-java}/io/micrometer/core/instrument/binder/system/DiskSpaceMetricsTest.java[tags=example, indent=0]
+-----
+
+[[system-file]]
+== System File Descriptor Metrics
+
+[source,java,subs=+attributes]
+-----
+// Usage example
+include::{include-core-test-java}/io/micrometer/core/instrument/binder/system/FileDescriptorMetricsTest.java[tags=example, indent=0]
+-----
+
+[[system-processor]]
+== System Processor Metrics
+
+[source,java,subs=+attributes]
+-----
+// Instrumentation setup
+include::{include-core-test-java}/io/micrometer/core/instrument/binder/system/ProcessorMetricsTest.java[tags=setup, indent=0]
+
+// Usage example
+include::{include-core-test-java}/io/micrometer/core/instrument/binder/system/ProcessorMetricsTest.java[tags=example, indent=0]
+-----
+
+[[system-uptime]]
+== System Uptime Metrics
+
+[source,java,subs=+attributes]
+-----
+// Usage example
+include::{include-core-test-java}/io/micrometer/core/instrument/binder/system/UptimeMetricsTest.java[tags=example, indent=0]
+-----

micrometer-core/src/test/java/io/micrometer/core/instrument/binder/system/DiskSpaceMetricsTest.java

@@ -37,10 +37,12 @@ class DiskSpaceMetricsTest {
 
     @Test
     void diskSpaceMetrics() {
+        // tag::example[]
         new DiskSpaceMetrics(new File(System.getProperty("user.dir"))).bindTo(registry);
 
         assertThat(registry.get("disk.free").gauge().value()).isNotNaN().isGreaterThan(0);
         assertThat(registry.get("disk.total").gauge().value()).isNotNaN().isGreaterThan(0);
+        // end::example[]
     }
 
     @Test

micrometer-core/src/test/java/io/micrometer/core/instrument/binder/system/FileDescriptorMetricsTest.java

@@ -49,10 +49,12 @@ void fileDescriptorMetricsUnsupportedOsBeanMock() {
     void unixFileDescriptorMetrics() {
         assumeFalse(System.getProperty("os.name").toLowerCase().contains("win"));
 
+        // tag::example[]
         new FileDescriptorMetrics(Tags.of("some", "tag")).bindTo(registry);
 
         assertThat(registry.get("process.files.open").tags("some", "tag").gauge().value()).isGreaterThan(0);
         assertThat(registry.get("process.files.max").tags("some", "tag").gauge().value()).isGreaterThan(0);
+        // end::example[]
     }
 
     @Test

micrometer-core/src/test/java/io/micrometer/core/instrument/binder/system/ProcessorMetricsTest.java

@@ -41,7 +41,9 @@ class ProcessorMetricsTest {
 
     @BeforeEach
     void setup() {
+        // tag::setup[]
         new ProcessorMetrics().bindTo(registry);
+        // end::setup[]
     }
 
     @Test
@@ -59,8 +61,10 @@ void cpuMetrics() {
     void hotspotCpuMetrics() {
         assumeTrue(!isOpenJ9());
 
+        // tag::example[]
         assertThat(registry.get("system.cpu.usage").gauge().value()).isNotNegative();
         assertThat(registry.get("process.cpu.usage").gauge().value()).isNotNegative();
+        // end::example[]
     }
 
     @Test

micrometer-core/src/test/java/io/micrometer/core/instrument/binder/system/UptimeMetricsTest.java

@@ -46,14 +46,16 @@ void uptimeMetricsRuntime() {
 
     @Test
     void uptimeMetricsMock() {
-        MeterRegistry registry = new SimpleMeterRegistry(SimpleConfig.DEFAULT, new MockClock());
         RuntimeMXBean runtimeMXBean = mock(RuntimeMXBean.class);
         when(runtimeMXBean.getUptime()).thenReturn(1337L);
         when(runtimeMXBean.getStartTime()).thenReturn(4711L);
+        // tag::example[]
+        MeterRegistry registry = new SimpleMeterRegistry(SimpleConfig.DEFAULT, new MockClock());
         new UptimeMetrics(runtimeMXBean, emptyList()).bindTo(registry);
 
         assertThat(registry.get("process.uptime").timeGauge().value()).isEqualTo(1.337);
         assertThat(registry.get("process.start.time").timeGauge().value()).isEqualTo(4.711);
+        // end::example[]
     }
 
 }