Add metrics support for idle jdbc connections

See gh-17504

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

@@ -38,6 +38,7 @@ import org.springframework.util.ConcurrentReferenceHashMap;
  *
  * @author Jon Schneider
  * @author Phillip Webb
+ * @author Artsiom Yudovin
  * @since 2.0.0
  */
 public class DataSourcePoolMetrics implements MeterBinder {
@@ -68,6 +69,7 @@ public class DataSourcePoolMetrics implements MeterBinder {
 			bindPoolMetadata(registry, "active", DataSourcePoolMetadata::getActive);
 			bindPoolMetadata(registry, "max", DataSourcePoolMetadata::getMax);
 			bindPoolMetadata(registry, "min", DataSourcePoolMetadata::getMin);
+			bindPoolMetadata(registry, "idle", DataSourcePoolMetadata::getIdle);
 		}
 	}
 

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

@@ -24,6 +24,7 @@ import org.apache.commons.dbcp2.BasicDataSource;
  * {@link DataSourcePoolMetadata} for an Apache Commons DBCP2 {@link DataSource}.
  *
  * @author Stephane Nicoll
+ * @author Artsiom Yudovin
  * @since 2.0.0
  */
 public class CommonsDbcp2DataSourcePoolMetadata extends AbstractDataSourcePoolMetadata<BasicDataSource> {
@@ -57,4 +58,9 @@ public class CommonsDbcp2DataSourcePoolMetadata extends AbstractDataSourcePoolMe
 		return getDataSource().getDefaultAutoCommit();
 	}
 
+	@Override
+	public Integer getIdle() {
+		return getDataSource().getNumIdle();
+	}
+
 }

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

@@ -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 +50,16 @@ 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
+	 */
+	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

@@ -16,6 +16,8 @@
 
 package org.springframework.boot.jdbc.metadata;
 
+import java.util.Objects;
+
 import javax.sql.DataSource;
 
 import com.zaxxer.hikari.HikariDataSource;
@@ -27,6 +29,7 @@ import org.springframework.beans.DirectFieldAccessor;
  * {@link DataSourcePoolMetadata} for a Hikari {@link DataSource}.
  *
  * @author Stephane Nicoll
+ * @author Artsiom Yudovin
  * @since 2.0.0
  */
 public class HikariDataSourcePoolMetadata extends AbstractDataSourcePoolMetadata<HikariDataSource> {
@@ -45,6 +48,16 @@ public class HikariDataSourcePoolMetadata extends AbstractDataSourcePoolMetadata
 		}
 	}
 
+	@Override
+	public Integer getIdle() {
+		HikariPool pool = getHikariPool();
+		if (Objects.nonNull(pool)) {
+			return pool.getIdleConnections();
+		}
+
+		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

@@ -23,6 +23,7 @@ import org.apache.tomcat.jdbc.pool.DataSource;
  * {@link DataSourcePoolMetadata} for a Tomcat DataSource.
  *
  * @author Stephane Nicoll
+ * @author Artsiom Yudovin
  * @since 2.0.0
  */
 public class TomcatDataSourcePoolMetadata extends AbstractDataSourcePoolMetadata<DataSource> {
@@ -57,4 +58,9 @@ public class TomcatDataSourcePoolMetadata extends AbstractDataSourcePoolMetadata
 		return getDataSource().isDefaultAutoCommit();
 	}
 
+	@Override
+	public Integer getIdle() {
+		return getDataSource().getNumIdle();
+	}
+
 }

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

@@ -29,6 +29,7 @@ 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<?>> {
 
@@ -67,6 +68,11 @@ abstract class AbstractDataSourcePoolMetadataTests<D extends AbstractDataSourceP
 		});
 	}
 
+	@Test
+	void getIdle() {
+		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

@@ -19,6 +19,9 @@ package org.springframework.boot.jdbc.metadata;
 import org.apache.commons.dbcp2.BasicDataSource;
 import org.junit.jupiter.api.Test;
 
+import org.springframework.jdbc.core.ConnectionCallback;
+import org.springframework.jdbc.core.JdbcTemplate;
+
 import static org.assertj.core.api.Assertions.assertThat;
 
 /**
@@ -83,6 +86,9 @@ class CommonsDbcp2DataSourcePoolMetadataTests
 		BasicDataSource dataSource = createDataSource();
 		dataSource.setMinIdle(minSize);
 		dataSource.setMaxTotal(maxSize);
+
+		this.initPool(dataSource);
+
 		return new CommonsDbcp2DataSourcePoolMetadata(dataSource);
 	}
 
@@ -90,4 +96,9 @@ class CommonsDbcp2DataSourcePoolMetadataTests
 		return initializeBuilder().type(BasicDataSource.class).build();
 	}
 
+	private void initPool(BasicDataSource dataSource) {
+		JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
+		jdbcTemplate.execute((ConnectionCallback<Void>) (connection) -> null);
+	}
+
 }

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

@@ -18,12 +18,16 @@ package org.springframework.boot.jdbc.metadata;
 
 import com.zaxxer.hikari.HikariDataSource;
 
+import org.springframework.jdbc.core.ConnectionCallback;
+import org.springframework.jdbc.core.JdbcTemplate;
+
 import static org.assertj.core.api.Assertions.assertThat;
 
 /**
  * Tests for {@link HikariDataSourcePoolMetadata}.
  *
  * @author Stephane Nicoll
+ * @author Artsiom Yudovin
  */
 public class HikariDataSourcePoolMetadataTests
 		extends AbstractDataSourcePoolMetadataTests<HikariDataSourcePoolMetadata> {
@@ -54,7 +58,15 @@ public class HikariDataSourcePoolMetadataTests
 		HikariDataSource dataSource = initializeBuilder().type(HikariDataSource.class).build();
 		dataSource.setMinimumIdle(minSize);
 		dataSource.setMaximumPoolSize(maxSize);
+
+		this.initPool(dataSource);
+
 		return dataSource;
 	}
 
+	private void initPool(HikariDataSource dataSource) {
+		JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
+		jdbcTemplate.execute((ConnectionCallback<Void>) (connection) -> null);
+	}
+
 }

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

@@ -18,6 +18,9 @@ package org.springframework.boot.jdbc.metadata;
 
 import org.apache.tomcat.jdbc.pool.DataSource;
 
+import org.springframework.jdbc.core.ConnectionCallback;
+import org.springframework.jdbc.core.JdbcTemplate;
+
 import static org.assertj.core.api.Assertions.assertThat;
 
 /**
@@ -58,7 +61,15 @@ public class TomcatDataSourcePoolMetadataTests
 		// Avoid warnings
 		dataSource.setInitialSize(minSize);
 		dataSource.setMaxIdle(maxSize);
+
+		this.initPool(dataSource);
+
 		return dataSource;
 	}
 
+	private void initPool(DataSource dataSource) {
+		JdbcTemplate jdbcTemplate = new JdbcTemplate(dataSource);
+		jdbcTemplate.execute((ConnectionCallback<Void>) (connection) -> null);
+	}
+
 }