HibernateTransactionManager lazily acquires JDBC Connection

Aligned with HibernateJpaDialect, using ConnectionHandle as functional interface now. Also, LazyConnectionDataSourceProxy supports Connection holdability as applied by HibernateTransactionManager, for use with prepareConnection=true.

Issue: SPR-17216

spring-jdbc/src/main/java/org/springframework/jdbc/datasource/ConnectionHandle.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2016 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -27,6 +27,7 @@
  * @see SimpleConnectionHandle
  * @see ConnectionHolder
  */
+@FunctionalInterface
 public interface ConnectionHandle {
 
 	/**
@@ -36,8 +37,11 @@ public interface ConnectionHandle {
 
 	/**
 	 * Release the JDBC Connection that this handle refers to.
+	 * <p>The default implementation is empty, assuming that the lifecycle
+	 * of the connection is managed externally.
 	 * @param con the JDBC Connection to release
 	 */
-	void releaseConnection(Connection con);
+	default void releaseConnection(Connection con) {
+	}
 
 }

spring-jdbc/src/main/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxy.java

@@ -21,6 +21,7 @@
 import java.lang.reflect.Method;
 import java.lang.reflect.Proxy;
 import java.sql.Connection;
+import java.sql.ResultSet;
 import java.sql.SQLException;
 import javax.sql.DataSource;
 
@@ -256,14 +257,16 @@ private class LazyConnectionInvocationHandler implements InvocationHandler {
 		@Nullable
 		private String password;
 
-		private Boolean readOnly = Boolean.FALSE;
-
 		@Nullable
 		private Boolean autoCommit;
 
 		@Nullable
 		private Integer transactionIsolation;
 
+		private boolean readOnly = false;
+
+		private int holdability = ResultSet.CLOSE_CURSORS_AT_COMMIT;
+
 		private boolean closed = false;
 
 		@Nullable
@@ -319,11 +322,15 @@ else if (method.getName().equals("getTargetConnection")) {
 				if (method.getName().equals("toString")) {
 					return "Lazy Connection proxy for target DataSource [" + getTargetDataSource() + "]";
 				}
-				else if (method.getName().equals("isReadOnly")) {
-					return this.readOnly;
+				else if (method.getName().equals("getAutoCommit")) {
+					if (this.autoCommit != null) {
+						return this.autoCommit;
+					}
+					// Else fetch actual Connection and check there,
+					// because we didn't have a default specified.
 				}
-				else if (method.getName().equals("setReadOnly")) {
-					this.readOnly = (Boolean) args[0];
+				else if (method.getName().equals("setAutoCommit")) {
+					this.autoCommit = (Boolean) args[0];
 					return null;
 				}
 				else if (method.getName().equals("getTransactionIsolation")) {
@@ -337,15 +344,18 @@ else if (method.getName().equals("setTransactionIsolation")) {
 					this.transactionIsolation = (Integer) args[0];
 					return null;
 				}
-				else if (method.getName().equals("getAutoCommit")) {
-					if (this.autoCommit != null) {
-						return this.autoCommit;
-					}
-					// Else fetch actual Connection and check there,
-					// because we didn't have a default specified.
+				else if (method.getName().equals("isReadOnly")) {
+					return this.readOnly;
 				}
-				else if (method.getName().equals("setAutoCommit")) {
-					this.autoCommit = (Boolean) args[0];
+				else if (method.getName().equals("setReadOnly")) {
+					this.readOnly = (Boolean) args[0];
+					return null;
+				}
+				else if (method.getName().equals("getHoldability")) {
+					return this.holdability;
+				}
+				else if (method.getName().equals("setHoldability")) {
+					this.holdability = (Integer) args[0];
 					return null;
 				}
 				else if (method.getName().equals("commit")) {

spring-jdbc/src/main/java/org/springframework/jdbc/datasource/SimpleConnectionHandle.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2012 the original author or authors.
+ * Copyright 2002-2018 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.
@@ -49,14 +49,6 @@ public Connection getConnection() {
 		return this.connection;
 	}
 
-	/**
-	 * This implementation is empty, as we're using a standard
-	 * Connection handle that does not have to be released.
-	 */
-	@Override
-	public void releaseConnection(Connection con) {
-	}
-
 
 	@Override
 	public String toString() {

spring-orm/src/main/java/org/springframework/orm/hibernate5/HibernateTransactionManager.java

@@ -197,9 +197,16 @@ protected final SessionFactory obtainSessionFactory() {
 	 * manager needs to work on the underlying target DataSource. If there's
 	 * nevertheless a TransactionAwareDataSourceProxy passed in, it will be
 	 * unwrapped to extract its target DataSource.
+	 * <p><b>NOTE: For scenarios with many transactions that just read data from
+	 * Hibernate's cache (and do not actually access the database), consider using
+	 * a {@link org.springframework.jdbc.datasource.LazyConnectionDataSourceProxy}
+	 * for the actual target DataSource. Alternatively, consider switching
+	 * {@link #setPrepareConnection "prepareConnection"} to {@code false}.</b>
+	 * In both cases, this transaction manager will not eagerly acquire a
+	 * JDBC Connection for each Hibernate Session anymore (as of Spring 5.1).
 	 * @see #setAutodetectDataSource
 	 * @see TransactionAwareDataSourceProxy
-	 * @see DataSourceUtils
+	 * @see org.springframework.jdbc.datasource.LazyConnectionDataSourceProxy
 	 * @see org.springframework.jdbc.core.JdbcTemplate
 	 */
 	public void setDataSource(@Nullable DataSource dataSource) {
@@ -462,33 +469,37 @@ protected void doBegin(Object transaction, TransactionDefinition definition) {
 
 			session = txObject.getSessionHolder().getSession();
 
-			if (this.prepareConnection && isSameConnectionForEntireSession(session)) {
-				// We're allowed to change the transaction settings of the JDBC Connection.
-				if (logger.isDebugEnabled()) {
-					logger.debug("Preparing JDBC Connection of Hibernate Session [" + session + "]");
-				}
-				Connection con = ((SessionImplementor) session).connection();
-				Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
-				txObject.setPreviousIsolationLevel(previousIsolationLevel);
-				if (this.allowResultAccessAfterCompletion && !txObject.isNewSession()) {
-					int currentHoldability = con.getHoldability();
-					if (currentHoldability != ResultSet.HOLD_CURSORS_OVER_COMMIT) {
-						txObject.setPreviousHoldability(currentHoldability);
-						con.setHoldability(ResultSet.HOLD_CURSORS_OVER_COMMIT);
+			boolean holdabilityNeeded = this.allowResultAccessAfterCompletion && !txObject.isNewSession();
+			boolean isolationLevelNeeded = (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT);
+			if (holdabilityNeeded || isolationLevelNeeded || definition.isReadOnly()) {
+				if (this.prepareConnection && isSameConnectionForEntireSession(session)) {
+					// We're allowed to change the transaction settings of the JDBC Connection.
+					if (logger.isDebugEnabled()) {
+						logger.debug("Preparing JDBC Connection of Hibernate Session [" + session + "]");
+					}
+					Connection con = ((SessionImplementor) session).connection();
+					Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
+					txObject.setPreviousIsolationLevel(previousIsolationLevel);
+					if (this.allowResultAccessAfterCompletion && !txObject.isNewSession()) {
+						int currentHoldability = con.getHoldability();
+						if (currentHoldability != ResultSet.HOLD_CURSORS_OVER_COMMIT) {
+							txObject.setPreviousHoldability(currentHoldability);
+							con.setHoldability(ResultSet.HOLD_CURSORS_OVER_COMMIT);
+						}
 					}
 				}
-			}
-			else {
-				// Not allowed to change the transaction settings of the JDBC Connection.
-				if (definition.getIsolationLevel() != TransactionDefinition.ISOLATION_DEFAULT) {
-					// We should set a specific isolation level but are not allowed to...
-					throw new InvalidIsolationLevelException(
-							"HibernateTransactionManager is not allowed to support custom isolation levels: " +
-							"make sure that its 'prepareConnection' flag is on (the default) and that the " +
-							"Hibernate connection release mode is set to 'on_close' (the default for JDBC).");
-				}
-				if (logger.isDebugEnabled()) {
-					logger.debug("Not preparing JDBC Connection of Hibernate Session [" + session + "]");
+				else {
+					// Not allowed to change the transaction settings of the JDBC Connection.
+					if (isolationLevelNeeded) {
+						// We should set a specific isolation level but are not allowed to...
+						throw new InvalidIsolationLevelException(
+								"HibernateTransactionManager is not allowed to support custom isolation levels: " +
+								"make sure that its 'prepareConnection' flag is on (the default) and that the " +
+								"Hibernate connection release mode is set to 'on_close' (the default for JDBC).");
+					}
+					if (logger.isDebugEnabled()) {
+						logger.debug("Not preparing JDBC Connection of Hibernate Session [" + session + "]");
+					}
 				}
 			}
 
@@ -529,13 +540,13 @@ protected void doBegin(Object transaction, TransactionDefinition definition) {
 
 			// Register the Hibernate Session's JDBC Connection for the DataSource, if set.
 			if (getDataSource() != null) {
-				Connection con = ((SessionImplementor) session).connection();
-				ConnectionHolder conHolder = new ConnectionHolder(con);
+				SessionImplementor sessionImpl = (SessionImplementor) session;
+				ConnectionHolder conHolder = new ConnectionHolder(sessionImpl::connection);
 				if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
 					conHolder.setTimeoutInSeconds(timeout);
 				}
 				if (logger.isDebugEnabled()) {
-					logger.debug("Exposing Hibernate transaction as JDBC transaction [" + con + "]");
+					logger.debug("Exposing Hibernate transaction as JDBC [" + conHolder.getConnectionHandle() + "]");
 				}
 				TransactionSynchronizationManager.bindResource(getDataSource(), conHolder);
 				txObject.setConnectionHolder(conHolder);

spring-orm/src/main/java/org/springframework/orm/jpa/JpaTransactionManager.java

@@ -416,7 +416,7 @@ protected void doBegin(Object transaction, TransactionDefinition definition) {
 						conHolder.setTimeoutInSeconds(timeoutToUse);
 					}
 					if (logger.isDebugEnabled()) {
-						logger.debug("Exposing JPA transaction as JDBC transaction [" + conHandle + "]");
+						logger.debug("Exposing JPA transaction as JDBC [" + conHandle + "]");
 					}
 					TransactionSynchronizationManager.bindResource(getDataSource(), conHolder);
 					txObject.setConnectionHolder(conHolder);

spring-orm/src/main/java/org/springframework/orm/jpa/vendor/EclipseLinkJpaDialect.java

@@ -131,10 +131,6 @@ public Connection getConnection() {
 			}
 			return this.connection;
 		}
-
-		@Override
-		public void releaseConnection(Connection con) {
-		}
 	}
 
 }

spring-orm/src/main/java/org/springframework/orm/jpa/vendor/HibernateJpaDialect.java

@@ -75,7 +75,7 @@
 
 /**
  * {@link org.springframework.orm.jpa.JpaDialect} implementation for
- * Hibernate EntityManager. Developed against Hibernate 5.0/5.1/5.2.
+ * Hibernate EntityManager. Developed against Hibernate 5.1/5.2/5.3.
  *
  * @author Juergen Hoeller
  * @author Costin Leau
@@ -119,10 +119,8 @@ public class HibernateJpaDialect extends DefaultJpaDialect {
 	 * Hibernate Session, that is, whether to apply a transaction-specific
 	 * isolation level and/or the transaction's read-only flag to the underlying
 	 * JDBC Connection.
-	 * <p>Default is "true" on Hibernate EntityManager 4.x (with its 'on-close'
-	 * connection release mode.
-	 * <p>If you turn this flag off, JPA transaction management will not support
-	 * per-transaction isolation levels anymore. It will not call
+	 * <p>Default is "true". If you turn this flag off, JPA transaction management
+	 * will not support per-transaction isolation levels anymore. It will not call
 	 * {@code Connection.setReadOnly(true)} for read-only transactions anymore either.
 	 * If this flag is turned off, no cleanup of a JDBC Connection is required after
 	 * a transaction, since no Connection settings will get modified.
@@ -415,10 +413,6 @@ public Connection getConnection() {
 			return doGetConnection(this.session);
 		}
 
-		@Override
-		public void releaseConnection(Connection con) {
-		}
-
 		public static Connection doGetConnection(Session session) {
 			try {
 				Method methodToUse = connectionMethodToUse;

spring-orm/src/main/java/org/springframework/orm/jpa/vendor/HibernateJpaVendorAdapter.java

@@ -41,7 +41,7 @@
 
 /**
  * {@link org.springframework.orm.jpa.JpaVendorAdapter} implementation for Hibernate
- * EntityManager. Developed and tested against Hibernate 5.0, 5.1 and 5.2;
+ * EntityManager. Developed and tested against Hibernate 5.0, 5.1, 5.2 and 5.3;
  * backwards-compatible with Hibernate 4.3 at runtime on a best-effort basis.
  *
  * <p>Exposes Hibernate's persistence provider and EntityManager extension interface,