/*
 * Copyright 2002-2019 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.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.orm.hibernate5;

import java.sql.Connection;
import java.sql.ResultSet;

import javax.persistence.PersistenceException;
import javax.sql.DataSource;

import org.hibernate.ConnectionReleaseMode;
import org.hibernate.FlushMode;
import org.hibernate.HibernateException;
import org.hibernate.Interceptor;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.engine.spi.SessionImplementor;
import org.hibernate.resource.transaction.spi.TransactionStatus;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.dao.DataAccessException;
import org.springframework.dao.DataAccessResourceFailureException;
import org.springframework.jdbc.datasource.ConnectionHolder;
import org.springframework.jdbc.datasource.DataSourceUtils;
import org.springframework.jdbc.datasource.JdbcTransactionObjectSupport;
import org.springframework.jdbc.datasource.TransactionAwareDataSourceProxy;
import org.springframework.lang.Nullable;
import org.springframework.transaction.CannotCreateTransactionException;
import org.springframework.transaction.IllegalTransactionStateException;
import org.springframework.transaction.InvalidIsolationLevelException;
import org.springframework.transaction.TransactionDefinition;
import org.springframework.transaction.TransactionSystemException;
import org.springframework.transaction.support.AbstractPlatformTransactionManager;
import org.springframework.transaction.support.DefaultTransactionStatus;
import org.springframework.transaction.support.ResourceTransactionManager;
import org.springframework.transaction.support.TransactionSynchronizationManager;
import org.springframework.util.Assert;

/**
 * {@link org.springframework.transaction.PlatformTransactionManager}
 * implementation for a single Hibernate {@link SessionFactory}.
 * Binds a Hibernate Session from the specified factory to the thread,
 * potentially allowing for one thread-bound Session per factory.
 * {@code SessionFactory.getCurrentSession()} is required for Hibernate
 * access code that needs to support this transaction handling mechanism,
 * with the SessionFactory being configured with {@link SpringSessionContext}.
 *
 * <p>Supports custom isolation levels, and timeouts that get applied as
 * Hibernate transaction timeouts.
 *
 * <p>This transaction manager is appropriate for applications that use a single
 * Hibernate SessionFactory for transactional data access, but it also supports
 * direct DataSource access within a transaction (i.e. plain JDBC code working
 * with the same DataSource). This allows for mixing services which access Hibernate
 * and services which use plain JDBC (without being aware of Hibernate)!
 * Application code needs to stick to the same simple Connection lookup pattern as
 * with {@link org.springframework.jdbc.datasource.DataSourceTransactionManager}
 * (i.e. {@link org.springframework.jdbc.datasource.DataSourceUtils#getConnection}
 * or going through a
 * {@link org.springframework.jdbc.datasource.TransactionAwareDataSourceProxy}).
 *
 * <p>Note: To be able to register a DataSource's Connection for plain JDBC code,
 * this instance needs to be aware of the DataSource ({@link #setDataSource}).
 * The given DataSource should obviously match the one used by the given SessionFactory.
 *
 * <p>JTA (usually through {@link org.springframework.transaction.jta.JtaTransactionManager})
 * is necessary for accessing multiple transactional resources within the same
 * transaction. The DataSource that Hibernate uses needs to be JTA-enabled in
 * such a scenario (see container setup).
 *
 * <p>This transaction manager supports nested transactions via JDBC 3.0 Savepoints.
 * The {@link #setNestedTransactionAllowed} "nestedTransactionAllowed"} flag defaults
 * to "false", though, as nested transactions will just apply to the JDBC Connection,
 * not to the Hibernate Session and its cached entity objects and related context.
 * You can manually set the flag to "true" if you want to use nested transactions
 * for JDBC access code which participates in Hibernate transactions (provided that
 * your JDBC driver supports Savepoints). <i>Note that Hibernate itself does not
 * support nested transactions! Hence, do not expect Hibernate access code to
 * semantically participate in a nested transaction.</i>
 *
 * @author Juergen Hoeller
 * @since 4.2
 * @see #setSessionFactory
 * @see #setDataSource
 * @see SessionFactory#getCurrentSession()
 * @see DataSourceUtils#getConnection
 * @see DataSourceUtils#releaseConnection
 * @see org.springframework.jdbc.core.JdbcTemplate
 * @see org.springframework.jdbc.datasource.DataSourceTransactionManager
 * @see org.springframework.transaction.jta.JtaTransactionManager
 */
@SuppressWarnings("serial")
public class HibernateTransactionManager extends AbstractPlatformTransactionManager
                implements ResourceTransactionManager, BeanFactoryAware, InitializingBean {

        @Nullable
        private SessionFactory sessionFactory;

        @Nullable
        private DataSource dataSource;

        private boolean autodetectDataSource = true;

        private boolean prepareConnection = true;

        private boolean allowResultAccessAfterCompletion = false;

        private boolean hibernateManagedSession = false;

        @Nullable
        private Object entityInterceptor;

        /**
         * Just needed for entityInterceptorBeanName.
         * @see #setEntityInterceptorBeanName
         */
        @Nullable
        private BeanFactory beanFactory;


        /**
         * Create a new HibernateTransactionManager instance.
         * A SessionFactory has to be set to be able to use it.
         * @see #setSessionFactory
         */
        public HibernateTransactionManager() {
        }

        /**
         * Create a new HibernateTransactionManager instance.
         * @param sessionFactory the SessionFactory to manage transactions for
         */
        public HibernateTransactionManager(SessionFactory sessionFactory) {
                this.sessionFactory = sessionFactory;
                afterPropertiesSet();
        }


        /**
         * Set the SessionFactory that this instance should manage transactions for.
         */
        public void setSessionFactory(@Nullable SessionFactory sessionFactory) {
                this.sessionFactory = sessionFactory;
        }

        /**
         * Return the SessionFactory that this instance should manage transactions for.
         */
        @Nullable
        public SessionFactory getSessionFactory() {
                return this.sessionFactory;
        }

        /**
         * Obtain the SessionFactory for actual use.
         * @return the SessionFactory (never {@code null})
         * @throws IllegalStateException in case of no SessionFactory set
         * @since 5.0
         */
        protected final SessionFactory obtainSessionFactory() {
                SessionFactory sessionFactory = getSessionFactory();
                Assert.state(sessionFactory != null, "No SessionFactory set");
                return sessionFactory;
        }

        /**
         * Set the JDBC DataSource that this instance should manage transactions for.
         * The DataSource should match the one used by the Hibernate SessionFactory:
         * for example, you could specify the same JNDI DataSource for both.
         * <p>If the SessionFactory was configured with LocalDataSourceConnectionProvider,
         * i.e. by Spring's LocalSessionFactoryBean with a specified "dataSource",
         * the DataSource will be auto-detected: You can still explicitly specify the
         * DataSource, but you don't need to in this case.
         * <p>A transactional JDBC Connection for this DataSource will be provided to
         * application code accessing this DataSource directly via DataSourceUtils
         * or JdbcTemplate. The Connection will be taken from the Hibernate Session.
         * <p>The DataSource specified here should be the target DataSource to manage
         * transactions for, not a TransactionAwareDataSourceProxy. Only data access
         * code may work with TransactionAwareDataSourceProxy, while the transaction
         * 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 org.springframework.jdbc.datasource.LazyConnectionDataSourceProxy
         * @see org.springframework.jdbc.core.JdbcTemplate
         */
        public void setDataSource(@Nullable DataSource dataSource) {
                if (dataSource instanceof TransactionAwareDataSourceProxy) {
                        // If we got a TransactionAwareDataSourceProxy, we need to perform transactions
                        // for its underlying target DataSource, else data access code won't see
                        // properly exposed transactions (i.e. transactions for the target DataSource).
                        this.dataSource = ((TransactionAwareDataSourceProxy) dataSource).getTargetDataSource();
                }
                else {
                        this.dataSource = dataSource;
                }
        }

        /**
         * Return the JDBC DataSource that this instance manages transactions for.
         */
        @Nullable
        public DataSource getDataSource() {
                return this.dataSource;
        }

        /**
         * Set whether to autodetect a JDBC DataSource used by the Hibernate SessionFactory,
         * if set via LocalSessionFactoryBean's {@code setDataSource}. Default is "true".
         * <p>Can be turned off to deliberately ignore an available DataSource, in order
         * to not expose Hibernate transactions as JDBC transactions for that DataSource.
         * @see #setDataSource
         */
        public void setAutodetectDataSource(boolean autodetectDataSource) {
                this.autodetectDataSource = autodetectDataSource;
        }

        /**
         * Set whether to prepare the underlying JDBC Connection of a transactional
         * 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". If you turn this flag off, the transaction manager
         * 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.
         * @see Connection#setTransactionIsolation
         * @see Connection#setReadOnly
         */
        public void setPrepareConnection(boolean prepareConnection) {
                this.prepareConnection = prepareConnection;
        }

        /**
         * Set whether to allow result access after completion, typically via Hibernate's
         * ScrollableResults mechanism.
         * <p>Default is "false". Turning this flag on enforces over-commit holdability on the
         * underlying JDBC Connection (if {@link #prepareConnection "prepareConnection"} is on)
         * and skips the disconnect-on-completion step.
         * @see Connection#setHoldability
         * @see ResultSet#HOLD_CURSORS_OVER_COMMIT
         * @see #disconnectOnCompletion(Session)
         */
        public void setAllowResultAccessAfterCompletion(boolean allowResultAccessAfterCompletion) {
                this.allowResultAccessAfterCompletion = allowResultAccessAfterCompletion;
        }

        /**
         * Set whether to operate on a Hibernate-managed Session instead of a
         * Spring-managed Session, that is, whether to obtain the Session through
         * Hibernate's {@link SessionFactory#getCurrentSession()}
         * instead of {@link SessionFactory#openSession()} (with a Spring
         * {@link TransactionSynchronizationManager}
         * check preceding it).
         * <p>Default is "false", i.e. using a Spring-managed Session: taking the current
         * thread-bound Session if available (e.g. in an Open-Session-in-View scenario),
         * creating a new Session for the current transaction otherwise.
         * <p>Switch this flag to "true" in order to enforce use of a Hibernate-managed Session.
         * Note that this requires {@link SessionFactory#getCurrentSession()}
         * to always return a proper Session when called for a Spring-managed transaction;
         * transaction begin will fail if the {@code getCurrentSession()} call fails.
         * <p>This mode will typically be used in combination with a custom Hibernate
         * {@link org.hibernate.context.spi.CurrentSessionContext} implementation that stores
         * Sessions in a place other than Spring's TransactionSynchronizationManager.
         * It may also be used in combination with Spring's Open-Session-in-View support
         * (using Spring's default {@link SpringSessionContext}), in which case it subtly
         * differs from the Spring-managed Session mode: The pre-bound Session will <i>not</i>
         * receive a {@code clear()} call (on rollback) or a {@code disconnect()}
         * call (on transaction completion) in such a scenario; this is rather left up
         * to a custom CurrentSessionContext implementation (if desired).
         */
        public void setHibernateManagedSession(boolean hibernateManagedSession) {
                this.hibernateManagedSession = hibernateManagedSession;
        }

        /**
         * Set the bean name of a Hibernate entity interceptor that allows to inspect
         * and change property values before writing to and reading from the database.
         * Will get applied to any new Session created by this transaction manager.
         * <p>Requires the bean factory to be known, to be able to resolve the bean
         * name to an interceptor instance on session creation. Typically used for
         * prototype interceptors, i.e. a new interceptor instance per session.
         * <p>Can also be used for shared interceptor instances, but it is recommended
         * to set the interceptor reference directly in such a scenario.
         * @param entityInterceptorBeanName the name of the entity interceptor in
         * the bean factory
         * @see #setBeanFactory
         * @see #setEntityInterceptor
         */
        public void setEntityInterceptorBeanName(String entityInterceptorBeanName) {
                this.entityInterceptor = entityInterceptorBeanName;
        }

        /**
         * Set a Hibernate entity interceptor that allows to inspect and change
         * property values before writing to and reading from the database.
         * Will get applied to any new Session created by this transaction manager.
         * <p>Such an interceptor can either be set at the SessionFactory level,
         * i.e. on LocalSessionFactoryBean, or at the Session level, i.e. on
         * HibernateTransactionManager.
         * @see LocalSessionFactoryBean#setEntityInterceptor
         */
        public void setEntityInterceptor(@Nullable Interceptor entityInterceptor) {
                this.entityInterceptor = entityInterceptor;
        }

        /**
         * Return the current Hibernate entity interceptor, or {@code null} if none.
         * Resolves an entity interceptor bean name via the bean factory,
         * if necessary.
         * @throws IllegalStateException if bean name specified but no bean factory set
         * @throws BeansException if bean name resolution via the bean factory failed
         * @see #setEntityInterceptor
         * @see #setEntityInterceptorBeanName
         * @see #setBeanFactory
         */
        @Nullable
        public Interceptor getEntityInterceptor() throws IllegalStateException, BeansException {
                if (this.entityInterceptor instanceof Interceptor) {
                        return (Interceptor) this.entityInterceptor;
                }
                else if (this.entityInterceptor instanceof String) {
                        if (this.beanFactory == null) {
                                throw new IllegalStateException("Cannot get entity interceptor via bean name if no bean factory set");
                        }
                        String beanName = (String) this.entityInterceptor;
                        return this.beanFactory.getBean(beanName, Interceptor.class);
                }
                else {
                        return null;
                }
        }

        /**
         * The bean factory just needs to be known for resolving entity interceptor
         * bean names. It does not need to be set for any other mode of operation.
         * @see #setEntityInterceptorBeanName
         */
        @Override
        public void setBeanFactory(BeanFactory beanFactory) {
                this.beanFactory = beanFactory;
        }

        @Override
        public void afterPropertiesSet() {
                if (getSessionFactory() == null) {
                        throw new IllegalArgumentException("Property 'sessionFactory' is required");
                }
                if (this.entityInterceptor instanceof String && this.beanFactory == null) {
                        throw new IllegalArgumentException("Property 'beanFactory' is required for 'entityInterceptorBeanName'");
                }

                // Check for SessionFactory's DataSource.
                if (this.autodetectDataSource && getDataSource() == null) {
                        DataSource sfds = SessionFactoryUtils.getDataSource(getSessionFactory());
                        if (sfds != null) {
                                // Use the SessionFactory's DataSource for exposing transactions to JDBC code.
                                if (logger.isDebugEnabled()) {
                                        logger.debug("Using DataSource [" + sfds +
                                                        "] of Hibernate SessionFactory for HibernateTransactionManager");
                                }
                                setDataSource(sfds);
                        }
                }
        }


        @Override
        public Object getResourceFactory() {
                return obtainSessionFactory();
        }

        @Override
        protected Object doGetTransaction() {
                HibernateTransactionObject txObject = new HibernateTransactionObject();
                txObject.setSavepointAllowed(isNestedTransactionAllowed());

                SessionFactory sessionFactory = obtainSessionFactory();
                SessionHolder sessionHolder =
                                (SessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);
                if (sessionHolder != null) {
                        if (logger.isDebugEnabled()) {
                                logger.debug("Found thread-bound Session [" + sessionHolder.getSession() + "] for Hibernate transaction");
                        }
                        txObject.setSessionHolder(sessionHolder);
                }
                else if (this.hibernateManagedSession) {
                        try {
                                Session session = sessionFactory.getCurrentSession();
                                if (logger.isDebugEnabled()) {
                                        logger.debug("Found Hibernate-managed Session [" + session + "] for Spring-managed transaction");
                                }
                                txObject.setExistingSession(session);
                        }
                        catch (HibernateException ex) {
                                throw new DataAccessResourceFailureException(
                                                "Could not obtain Hibernate-managed Session for Spring-managed transaction", ex);
                        }
                }

                if (getDataSource() != null) {
                        ConnectionHolder conHolder = (ConnectionHolder)
                                        TransactionSynchronizationManager.getResource(getDataSource());
                        txObject.setConnectionHolder(conHolder);
                }

                return txObject;
        }

        @Override
        protected boolean isExistingTransaction(Object transaction) {
                HibernateTransactionObject txObject = (HibernateTransactionObject) transaction;
                return (txObject.hasSpringManagedTransaction() ||
                                (this.hibernateManagedSession && txObject.hasHibernateManagedTransaction()));
        }

        @Override
        @SuppressWarnings("deprecation")
        protected void doBegin(Object transaction, TransactionDefinition definition) {
                HibernateTransactionObject txObject = (HibernateTransactionObject) transaction;

                if (txObject.hasConnectionHolder() && !txObject.getConnectionHolder().isSynchronizedWithTransaction()) {
                        throw new IllegalTransactionStateException(
                                        "Pre-bound JDBC Connection found! HibernateTransactionManager does not support " +
                                        "running within DataSourceTransactionManager if told to manage the DataSource itself. " +
                                        "It is recommended to use a single HibernateTransactionManager for all transactions " +
                                        "on a single DataSource, no matter whether Hibernate or JDBC access.");
                }

                Session session = null;

                try {
                        if (!txObject.hasSessionHolder() || txObject.getSessionHolder().isSynchronizedWithTransaction()) {
                                Interceptor entityInterceptor = getEntityInterceptor();
                                Session newSession = (entityInterceptor != null ?
                                                obtainSessionFactory().withOptions().interceptor(entityInterceptor).openSession() :
                                                obtainSessionFactory().openSession());
                                if (logger.isDebugEnabled()) {
                                        logger.debug("Opened new Session [" + newSession + "] for Hibernate transaction");
                                }
                                txObject.setSession(newSession);
                        }

                        session = txObject.getSessionHolder().getSession();

                        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);
                                        txObject.setReadOnly(definition.isReadOnly());
                                        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 (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 + "]");
                                        }
                                }
                        }

                        if (definition.isReadOnly() && txObject.isNewSession()) {
                                // Just set to MANUAL in case of a new Session for this transaction.
                                session.setFlushMode(FlushMode.MANUAL);
                                // As of 5.1, we're also setting Hibernate's read-only entity mode by default.
                                session.setDefaultReadOnly(true);
                        }

                        if (!definition.isReadOnly() && !txObject.isNewSession()) {
                                // We need AUTO or COMMIT for a non-read-only transaction.
                                FlushMode flushMode = SessionFactoryUtils.getFlushMode(session);
                                if (FlushMode.MANUAL.equals(flushMode)) {
                                        session.setFlushMode(FlushMode.AUTO);
                                        txObject.getSessionHolder().setPreviousFlushMode(flushMode);
                                }
                        }

                        Transaction hibTx;

                        // Register transaction timeout.
                        int timeout = determineTimeout(definition);
                        if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
                                // Use Hibernate's own transaction timeout mechanism on Hibernate 3.1+
                                // Applies to all statements, also to inserts, updates and deletes!
                                hibTx = session.getTransaction();
                                hibTx.setTimeout(timeout);
                                hibTx.begin();
                        }
                        else {
                                // Open a plain Hibernate transaction without specified timeout.
                                hibTx = session.beginTransaction();
                        }

                        // Add the Hibernate transaction to the session holder.
                        txObject.getSessionHolder().setTransaction(hibTx);

                        // Register the Hibernate Session's JDBC Connection for the DataSource, if set.
                        if (getDataSource() != null) {
                                SessionImplementor sessionImpl = (SessionImplementor) session;
                                // The following needs to use a lambda expression instead of a method reference
                                // for compatibility with Hibernate ORM <5.2 where connection() is defined on
                                // SessionImplementor itself instead of on SharedSessionContractImplementor...
                                ConnectionHolder conHolder = new ConnectionHolder(() -> sessionImpl.connection());
                                if (timeout != TransactionDefinition.TIMEOUT_DEFAULT) {
                                        conHolder.setTimeoutInSeconds(timeout);
                                }
                                if (logger.isDebugEnabled()) {
                                        logger.debug("Exposing Hibernate transaction as JDBC [" + conHolder.getConnectionHandle() + "]");
                                }
                                TransactionSynchronizationManager.bindResource(getDataSource(), conHolder);
                                txObject.setConnectionHolder(conHolder);
                        }

                        // Bind the session holder to the thread.
                        if (txObject.isNewSessionHolder()) {
                                TransactionSynchronizationManager.bindResource(obtainSessionFactory(), txObject.getSessionHolder());
                        }
                        txObject.getSessionHolder().setSynchronizedWithTransaction(true);
                }

                catch (Throwable ex) {
                        if (txObject.isNewSession()) {
                                try {
                                        if (session != null && session.getTransaction().getStatus() == TransactionStatus.ACTIVE) {
                                                session.getTransaction().rollback();
                                        }
                                }
                                catch (Throwable ex2) {
                                        logger.debug("Could not rollback Session after failed transaction begin", ex);
                                }
                                finally {
                                        SessionFactoryUtils.closeSession(session);
                                        txObject.setSessionHolder(null);
                                }
                        }
                        throw new CannotCreateTransactionException("Could not open Hibernate Session for transaction", ex);
                }
        }

        @Override
        protected Object doSuspend(Object transaction) {
                HibernateTransactionObject txObject = (HibernateTransactionObject) transaction;
                txObject.setSessionHolder(null);
                SessionHolder sessionHolder =
                                (SessionHolder) TransactionSynchronizationManager.unbindResource(obtainSessionFactory());
                txObject.setConnectionHolder(null);
                ConnectionHolder connectionHolder = null;
                if (getDataSource() != null) {
                        connectionHolder = (ConnectionHolder) TransactionSynchronizationManager.unbindResource(getDataSource());
                }
                return new SuspendedResourcesHolder(sessionHolder, connectionHolder);
        }

        @Override
        protected void doResume(@Nullable Object transaction, Object suspendedResources) {
                SessionFactory sessionFactory = obtainSessionFactory();

                SuspendedResourcesHolder resourcesHolder = (SuspendedResourcesHolder) suspendedResources;
                if (TransactionSynchronizationManager.hasResource(sessionFactory)) {
                        // From non-transactional code running in active transaction synchronization
                        // -> can be safely removed, will be closed on transaction completion.
                        TransactionSynchronizationManager.unbindResource(sessionFactory);
                }
                TransactionSynchronizationManager.bindResource(sessionFactory, resourcesHolder.getSessionHolder());
                if (getDataSource() != null && resourcesHolder.getConnectionHolder() != null) {
                        TransactionSynchronizationManager.bindResource(getDataSource(), resourcesHolder.getConnectionHolder());
                }
        }

        @Override
        protected void doCommit(DefaultTransactionStatus status) {
                HibernateTransactionObject txObject = (HibernateTransactionObject) status.getTransaction();
                Transaction hibTx = txObject.getSessionHolder().getTransaction();
                Assert.state(hibTx != null, "No Hibernate transaction");
                if (status.isDebug()) {
                        logger.debug("Committing Hibernate transaction on Session [" +
                                        txObject.getSessionHolder().getSession() + "]");
                }

                try {
                        hibTx.commit();
                }
                catch (org.hibernate.TransactionException ex) {
                        // assumably from commit call to the underlying JDBC connection
                        throw new TransactionSystemException("Could not commit Hibernate transaction", ex);
                }
                catch (HibernateException ex) {
                        // assumably failed to flush changes to database
                        throw convertHibernateAccessException(ex);
                }
                catch (PersistenceException ex) {
                        if (ex.getCause() instanceof HibernateException) {
                                throw convertHibernateAccessException((HibernateException) ex.getCause());
                        }
                        throw ex;
                }
        }

        @Override
        protected void doRollback(DefaultTransactionStatus status) {
                HibernateTransactionObject txObject = (HibernateTransactionObject) status.getTransaction();
                Transaction hibTx = txObject.getSessionHolder().getTransaction();
                Assert.state(hibTx != null, "No Hibernate transaction");
                if (status.isDebug()) {
                        logger.debug("Rolling back Hibernate transaction on Session [" +
                                        txObject.getSessionHolder().getSession() + "]");
                }

                try {
                        hibTx.rollback();
                }
                catch (org.hibernate.TransactionException ex) {
                        throw new TransactionSystemException("Could not roll back Hibernate transaction", ex);
                }
                catch (HibernateException ex) {
                        // Shouldn't really happen, as a rollback doesn't cause a flush.
                        throw convertHibernateAccessException(ex);
                }
                catch (PersistenceException ex) {
                        if (ex.getCause() instanceof HibernateException) {
                                throw convertHibernateAccessException((HibernateException) ex.getCause());
                        }
                        throw ex;
                }
                finally {
                        if (!txObject.isNewSession() && !this.hibernateManagedSession) {
                                // Clear all pending inserts/updates/deletes in the Session.
                                // Necessary for pre-bound Sessions, to avoid inconsistent state.
                                txObject.getSessionHolder().getSession().clear();
                        }
                }
        }

        @Override
        protected void doSetRollbackOnly(DefaultTransactionStatus status) {
                HibernateTransactionObject txObject = (HibernateTransactionObject) status.getTransaction();
                if (status.isDebug()) {
                        logger.debug("Setting Hibernate transaction on Session [" +
                                        txObject.getSessionHolder().getSession() + "] rollback-only");
                }
                txObject.setRollbackOnly();
        }

        @Override
        @SuppressWarnings("deprecation")
        protected void doCleanupAfterCompletion(Object transaction) {
                HibernateTransactionObject txObject = (HibernateTransactionObject) transaction;

                // Remove the session holder from the thread.
                if (txObject.isNewSessionHolder()) {
                        TransactionSynchronizationManager.unbindResource(obtainSessionFactory());
                }

                // Remove the JDBC connection holder from the thread, if exposed.
                if (getDataSource() != null) {
                        TransactionSynchronizationManager.unbindResource(getDataSource());
                }

                Session session = txObject.getSessionHolder().getSession();
                if (this.prepareConnection && isPhysicallyConnected(session)) {
                        // We're running with connection release mode "on_close": We're able to reset
                        // the isolation level and/or read-only flag of the JDBC Connection here.
                        // Else, we need to rely on the connection pool to perform proper cleanup.
                        try {
                                Connection con = ((SessionImplementor) session).connection();
                                Integer previousHoldability = txObject.getPreviousHoldability();
                                if (previousHoldability != null) {
                                        con.setHoldability(previousHoldability);
                                }
                                DataSourceUtils.resetConnectionAfterTransaction(
                                                con, txObject.getPreviousIsolationLevel(), txObject.isReadOnly());
                        }
                        catch (HibernateException ex) {
                                logger.debug("Could not access JDBC Connection of Hibernate Session", ex);
                        }
                        catch (Throwable ex) {
                                logger.debug("Could not reset JDBC Connection after transaction", ex);
                        }
                }

                if (txObject.isNewSession()) {
                        if (logger.isDebugEnabled()) {
                                logger.debug("Closing Hibernate Session [" + session + "] after transaction");
                        }
                        SessionFactoryUtils.closeSession(session);
                }
                else {
                        if (logger.isDebugEnabled()) {
                                logger.debug("Not closing pre-bound Hibernate Session [" + session + "] after transaction");
                        }
                        if (txObject.getSessionHolder().getPreviousFlushMode() != null) {
                                session.setFlushMode(txObject.getSessionHolder().getPreviousFlushMode());
                        }
                        if (!this.allowResultAccessAfterCompletion && !this.hibernateManagedSession) {
                                disconnectOnCompletion(session);
                        }
                }
                txObject.getSessionHolder().clear();
        }

        /**
         * Disconnect a pre-existing Hibernate Session on transaction completion,
         * returning its database connection but preserving its entity state.
         * <p>The default implementation simply calls {@link Session#disconnect()}.
         * Subclasses may override this with a no-op or with fine-tuned disconnection logic.
         * @param session the Hibernate Session to disconnect
         * @see Session#disconnect()
         */
        protected void disconnectOnCompletion(Session session) {
                session.disconnect();
        }

        /**
         * Return whether the given Hibernate Session will always hold the same
         * JDBC Connection. This is used to check whether the transaction manager
         * can safely prepare and clean up the JDBC Connection used for a transaction.
         * <p>The default implementation checks the Session's connection release mode
         * to be "on_close".
         * @param session the Hibernate Session to check
         * @see ConnectionReleaseMode#ON_CLOSE
         */
        @SuppressWarnings("deprecation")
        protected boolean isSameConnectionForEntireSession(Session session) {
                if (!(session instanceof SessionImplementor)) {
                        // The best we can do is to assume we're safe.
                        return true;
                }
                ConnectionReleaseMode releaseMode =
                                ((SessionImplementor) session).getJdbcCoordinator().getConnectionReleaseMode();
                return ConnectionReleaseMode.ON_CLOSE.equals(releaseMode);
        }

        /**
         * Determine whether the given Session is (still) physically connected
         * to the database, that is, holds an active JDBC Connection internally.
         * @param session the Hibernate Session to check
         * @see #isSameConnectionForEntireSession(Session)
         */
        protected boolean isPhysicallyConnected(Session session) {
                if (!(session instanceof SessionImplementor)) {
                        // The best we can do is to check whether we're logically connected.
                        return session.isConnected();
                }
                return ((SessionImplementor) session).getJdbcCoordinator().getLogicalConnection().isPhysicallyConnected();
        }


        /**
         * Convert the given HibernateException to an appropriate exception
         * from the {@code org.springframework.dao} hierarchy.
         * <p>Will automatically apply a specified SQLExceptionTranslator to a
         * Hibernate JDBCException, else rely on Hibernate's default translation.
         * @param ex the HibernateException that occurred
         * @return a corresponding DataAccessException
         * @see SessionFactoryUtils#convertHibernateAccessException
         */
        protected DataAccessException convertHibernateAccessException(HibernateException ex) {
                return SessionFactoryUtils.convertHibernateAccessException(ex);
        }


        /**
         * Hibernate transaction object, representing a SessionHolder.
         * Used as transaction object by HibernateTransactionManager.
         */
        private class HibernateTransactionObject extends JdbcTransactionObjectSupport {

                @Nullable
                private SessionHolder sessionHolder;

                private boolean newSessionHolder;

                private boolean newSession;

                @Nullable
                private Integer previousHoldability;

                public void setSession(Session session) {
                        this.sessionHolder = new SessionHolder(session);
                        this.newSessionHolder = true;
                        this.newSession = true;
                }

                public void setExistingSession(Session session) {
                        this.sessionHolder = new SessionHolder(session);
                        this.newSessionHolder = true;
                        this.newSession = false;
                }

                public void setSessionHolder(@Nullable SessionHolder sessionHolder) {
                        this.sessionHolder = sessionHolder;
                        this.newSessionHolder = false;
                        this.newSession = false;
                }

                public SessionHolder getSessionHolder() {
                        Assert.state(this.sessionHolder != null, "No SessionHolder available");
                        return this.sessionHolder;
                }

                public boolean hasSessionHolder() {
                        return (this.sessionHolder != null);
                }

                public boolean isNewSessionHolder() {
                        return this.newSessionHolder;
                }

                public boolean isNewSession() {
                        return this.newSession;
                }

                public void setPreviousHoldability(@Nullable Integer previousHoldability) {
                        this.previousHoldability = previousHoldability;
                }

                @Nullable
                public Integer getPreviousHoldability() {
                        return this.previousHoldability;
                }

                public boolean hasSpringManagedTransaction() {
                        return (this.sessionHolder != null && this.sessionHolder.getTransaction() != null);
                }

                public boolean hasHibernateManagedTransaction() {
                        return (this.sessionHolder != null &&
                                        this.sessionHolder.getSession().getTransaction().getStatus() == TransactionStatus.ACTIVE);
                }

                public void setRollbackOnly() {
                        getSessionHolder().setRollbackOnly();
                        if (hasConnectionHolder()) {
                                getConnectionHolder().setRollbackOnly();
                        }
                }

                @Override
                public boolean isRollbackOnly() {
                        return getSessionHolder().isRollbackOnly() ||
                                        (hasConnectionHolder() && getConnectionHolder().isRollbackOnly());
                }

                @Override
                public void flush() {
                        try {
                                getSessionHolder().getSession().flush();
                        }
                        catch (HibernateException ex) {
                                throw convertHibernateAccessException(ex);
                        }
                        catch (PersistenceException ex) {
                                if (ex.getCause() instanceof HibernateException) {
                                        throw convertHibernateAccessException((HibernateException) ex.getCause());
                                }
                                throw ex;
                        }
                }
        }


        /**
         * Holder for suspended resources.
         * Used internally by {@code doSuspend} and {@code doResume}.
         */
        private static final class SuspendedResourcesHolder {

                private final SessionHolder sessionHolder;

                @Nullable
                private final ConnectionHolder connectionHolder;

                private SuspendedResourcesHolder(SessionHolder sessionHolder, @Nullable ConnectionHolder conHolder) {
                        this.sessionHolder = sessionHolder;
                        this.connectionHolder = conHolder;
                }

                private SessionHolder getSessionHolder() {
                        return this.sessionHolder;
                }

                @Nullable
                private ConnectionHolder getConnectionHolder() {
                        return this.connectionHolder;
                }
        }

}