Fix for empty datasource-name in metrics

If there is more than one DataSource and the non-primary bean-name is
'datasource' an incorrect metric name is chosen.

The metrics are named datasource.active and not datasource.xxx.active. To
avoid this, the shortening of the bean-name only occurs if the bean-name
is longer than 'datasource'.

See gh-2320

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

@@ -102,7 +102,8 @@ public class DataSourcePublicMetrics implements PublicMetrics {
 		if (primary) {
 			return "datasource.primary";
 		}
-		if (name.toLowerCase().endsWith(DATASOURCE_SUFFIX.toLowerCase())) {
+		if (name.length() > DATASOURCE_SUFFIX.length()
+				&& name.toLowerCase().endsWith(DATASOURCE_SUFFIX.toLowerCase())) {
 			name = name.substring(0, name.length() - DATASOURCE_SUFFIX.length());
 		}
 		return "datasource." + name;

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

@@ -168,6 +168,15 @@ public class PublicMetricsAutoConfigurationTests {
 				"datasource.commonsDbcp.active", "datasource.commonsDbcp.usage");
 	}
 
+	@Test
+	public void multipleDataSourcesWithCustomPrimary() {
+		load(MultipleDataSourcesWithCustomPrimaryConfig.class);
+		PublicMetrics bean = this.context.getBean(DataSourcePublicMetrics.class);
+		Collection<Metric<?>> metrics = bean.metrics();
+		assertMetrics(metrics, "datasource.primary.active", "datasource.primary.usage",
+				"datasource.dataSource.active", "datasource.dataSource.usage");
+	}
+
 	@Test
 	public void customPrefix() {
 		load(MultipleDataSourcesWithPrimaryConfig.class,
@@ -250,6 +259,22 @@ public class PublicMetricsAutoConfigurationTests {
 		}
 	}
 
+	@Configuration
+	static class MultipleDataSourcesWithCustomPrimaryConfig {
+
+		@Bean
+		@Primary
+		public DataSource myDataSource() {
+			return initializeBuilder().type(org.apache.tomcat.jdbc.pool.DataSource.class)
+					.build();
+		}
+
+		@Bean
+		public DataSource dataSource() {
+			return initializeBuilder().type(BasicDataSource.class).build();
+		}
+	}
+
 	@Configuration
 	static class CustomDataSourcePublicMetrics {