Allow counter names like counter-foo

Checking for a prefix "counter." is more correct than "counter" because
the readers (repositories) assume the former prefix is there.

Fixes gh-3801

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/writer/DefaultCounterService.java

@@ -58,7 +58,7 @@ public class DefaultCounterService implements CounterService {
 		if (this.names.containsKey(metricName)) {
 			return this.names.get(metricName);
 		}
-		if (metricName.startsWith("counter") || metricName.startsWith("meter")) {
+		if (metricName.startsWith("counter.") || metricName.startsWith("meter.")) {
 			return metricName;
 		}
 		String name = "counter." + metricName;

spring-boot-actuator/src/test/java/org/springframework/boot/actuate/metrics/writer/DefaultCounterServiceTests.java

@@ -16,16 +16,16 @@
 
 package org.springframework.boot.actuate.metrics.writer;
 
+import static org.junit.Assert.assertEquals;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verify;
+
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.mockito.ArgumentCaptor;
 import org.mockito.Captor;
 import org.mockito.runners.MockitoJUnitRunner;
 
-import static org.junit.Assert.assertEquals;
-import static org.mockito.Mockito.mock;
-import static org.mockito.Mockito.verify;
-
 /**
  * Tests for {@link DefaultCounterService}.
  */
@@ -40,6 +40,22 @@ public class DefaultCounterServiceTests {
 	@Captor
 	private ArgumentCaptor<Delta<Number>> captor;
 
+	@Test
+	public void incrementWithExistingCounter() {
+		this.service.increment("counter.foo");
+		verify(this.repository).increment(this.captor.capture());
+		assertEquals("counter.foo", this.captor.getValue().getName());
+		assertEquals(1L, this.captor.getValue().getValue());
+	}
+
+	@Test
+	public void incrementWithExistingNearlyCounter() {
+		this.service.increment("counter-foo");
+		verify(this.repository).increment(this.captor.capture());
+		assertEquals("counter.counter-foo", this.captor.getValue().getName());
+		assertEquals(1L, this.captor.getValue().getValue());
+	}
+
 	@Test
 	public void incrementPrependsCounter() {
 		this.service.increment("foo");