Merge pull request #17504 from ayudovin

* pr/17504:
  Polish "Add metrics support for idle jdbc connections"
  Add metrics support for idle jdbc connections

Closes gh-17504

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/metrics/jdbc/DataSourcePoolMetrics.java

@@ -66,6 +66,7 @@ public class DataSourcePoolMetrics implements MeterBinder {
 	public void bindTo(MeterRegistry registry) {
 		if (this.metadataProvider.getDataSourcePoolMetadata(this.dataSource) != null) {
 			bindPoolMetadata(registry, "active", DataSourcePoolMetadata::getActive);
+			bindPoolMetadata(registry, "idle", DataSourcePoolMetadata::getIdle);
 			bindPoolMetadata(registry, "max", DataSourcePoolMetadata::getMax);
 			bindPoolMetadata(registry, "min", DataSourcePoolMetadata::getMin);
 		}

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

@@ -2023,8 +2023,8 @@ is required. A `CacheMetricsRegistrar` bean is made available to make that proce
 ==== DataSource Metrics
 Auto-configuration enables the instrumentation of all available `DataSource` objects with
 a metric named `jdbc`. Data source instrumentation results in gauges representing the
-currently active, maximum allowed, and minimum allowed connections in the pool. Each of
-these gauges has a name that is prefixed by `jdbc`.
+currently active, idle, maximum allowed, and minimum allowed connections in the pool. Each
+of these gauges has a name that is prefixed by `jdbc`.
 
 Metrics are also tagged by the name of the `DataSource` computed based on the bean name.
 

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/jdbc/metadata/CommonsDbcp2DataSourcePoolMetadata.java

@@ -37,6 +37,11 @@ public class CommonsDbcp2DataSourcePoolMetadata extends AbstractDataSourcePoolMe
 		return getDataSource().getNumActive();
 	}
 
+	@Override
+	public Integer getIdle() {
+		return getDataSource().getNumIdle();
+	}
+
 	@Override
 	public Integer getMax() {
 		return getDataSource().getMaxTotal();

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/jdbc/metadata/DataSourcePoolMetadata.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2017 the original author or authors.
+ * Copyright 2012-2019 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.
@@ -23,6 +23,7 @@ import javax.sql.DataSource;
  * {@link DataSource} implementations.
  *
  * @author Stephane Nicoll
+ * @author Artsiom Yudovin
  * @since 2.0.0
  */
 public interface DataSourcePoolMetadata {
@@ -49,6 +50,17 @@ public interface DataSourcePoolMetadata {
 	 */
 	Integer getActive();
 
+	/**
+	 * Return the number of established but idle connections. Can also return {@code null}
+	 * if that information is not available.
+	 * @return the number of established but idle connections or {@code null}
+	 * @since 2.2.0
+	 * @see #getActive()
+	 */
+	default Integer getIdle() {
+		return null;
+	}
+
 	/**
 	 * Return the maximum number of active connections that can be allocated at the same
 	 * time or {@code -1} if there is no limit. Can also return {@code null} if that

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/jdbc/metadata/HikariDataSourcePoolMetadata.java

@@ -45,6 +45,16 @@ public class HikariDataSourcePoolMetadata extends AbstractDataSourcePoolMetadata
 		}
 	}
 
+	@Override
+	public Integer getIdle() {
+		try {
+			return getHikariPool().getIdleConnections();
+		}
+		catch (Exception ex) {
+			return null;
+		}
+	}
+
 	private HikariPool getHikariPool() {
 		return (HikariPool) new DirectFieldAccessor(getDataSource()).getPropertyValue("pool");
 	}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/jdbc/metadata/TomcatDataSourcePoolMetadata.java

@@ -37,6 +37,11 @@ public class TomcatDataSourcePoolMetadata extends AbstractDataSourcePoolMetadata
 		return (pool != null) ? pool.getActive() : 0;
 	}
 
+	@Override
+	public Integer getIdle() {
+		return getDataSource().getNumIdle();
+	}
+
 	@Override
 	public Integer getMax() {
 		return getDataSource().getMaxActive();

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/jdbc/metadata/AbstractDataSourcePoolMetadataTests.java

@@ -29,11 +29,13 @@ import static org.assertj.core.api.Assertions.assertThat;
  *
  * @param <D> the data source pool metadata type
  * @author Stephane Nicoll
+ * @author Artsiom Yudovin
  */
 abstract class AbstractDataSourcePoolMetadataTests<D extends AbstractDataSourcePoolMetadata<?>> {
 
 	/**
-	 * Return a data source metadata instance with a min size of 0 and max size of 2.
+	 * Return a data source metadata instance with a min size of 0 and max size of 2. Idle
+	 * connections are not reclaimed immediately.
 	 * @return the data source metadata
 	 */
 	protected abstract D getDataSourceMetadata();
@@ -67,6 +69,13 @@ abstract class AbstractDataSourcePoolMetadataTests<D extends AbstractDataSourceP
 		});
 	}
 
+	@Test
+	void getIdle() {
+		JdbcTemplate jdbcTemplate = new JdbcTemplate(getDataSourceMetadata().getDataSource());
+		jdbcTemplate.execute((ConnectionCallback<Void>) (connection) -> null);
+		assertThat(getDataSourceMetadata().getIdle()).isEqualTo(Integer.valueOf(1));
+	}
+
 	@Test
 	void getPoolSizeTwoConnections() {
 		final JdbcTemplate jdbcTemplate = new JdbcTemplate(getDataSourceMetadata().getDataSource());

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/jdbc/metadata/CommonsDbcp2DataSourcePoolMetadataTests.java

@@ -83,6 +83,7 @@ class CommonsDbcp2DataSourcePoolMetadataTests
 		BasicDataSource dataSource = createDataSource();
 		dataSource.setMinIdle(minSize);
 		dataSource.setMaxTotal(maxSize);
+		dataSource.setMinEvictableIdleTimeMillis(5000);
 		return new CommonsDbcp2DataSourcePoolMetadata(dataSource);
 	}
 

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/jdbc/metadata/HikariDataSourcePoolMetadataTests.java

@@ -54,6 +54,7 @@ public class HikariDataSourcePoolMetadataTests
 		HikariDataSource dataSource = initializeBuilder().type(HikariDataSource.class).build();
 		dataSource.setMinimumIdle(minSize);
 		dataSource.setMaximumPoolSize(maxSize);
+		dataSource.setIdleTimeout(5000);
 		return dataSource;
 	}
 

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/jdbc/metadata/TomcatDataSourcePoolMetadataTests.java

@@ -54,6 +54,7 @@ public class TomcatDataSourcePoolMetadataTests
 		DataSource dataSource = initializeBuilder().type(DataSource.class).build();
 		dataSource.setMinIdle(minSize);
 		dataSource.setMaxActive(maxSize);
+		dataSource.setMinEvictableIdleTimeMillis(5000);
 
 		// Avoid warnings
 		dataSource.setInitialSize(minSize);