EDIT

/**

* Copyright (C) 2009 EDIT

* European Distributed Institute of Taxonomy

* http://www.e-taxonomy.eu

*

* The contents of this file are subject to the Mozilla Public License Version 1.1

* See LICENSE.TXT at the top of this package for the full license terms.

*/

package eu.etaxonomy.cdm.api.conversation;

import java.sql.SQLException;

import javax.sql.DataSource;

import org.apache.log4j.Logger;

import org.hibernate.FlushMode;

import org.hibernate.LockMode;

import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.springframework.beans.factory.annotation.Autowired;

import org.springframework.jdbc.datasource.ConnectionHolder;

import org.springframework.orm.hibernate5.SessionHolder;

import org.springframework.transaction.PlatformTransactionManager;

import org.springframework.transaction.TransactionDefinition;

import org.springframework.transaction.TransactionStatus;

import org.springframework.transaction.support.TransactionSynchronizationManager;

import eu.etaxonomy.cdm.persistence.hibernate.CdmPostDataChangeObservableListener;

/**

 * This is an implementation of the session-per-conversation pattern for usage in a Spring context.

 *

 * The primary aim of this class is to create and maintain sessions across multiple transactions.

 * It is important to ensure that these (long running) sessions must always behave consistently

 * with regards to session management behaviour expected by Hibernate.

 * <p>

 * This behaviour essentially revolves around the resources map in the {@link org.springframework.transaction.support.TransactionSynchronizationManager TransactionSynchronizationManager}.

 * This resources map contains two entries of interest,

 *  - (Autowired) {@link org.hibernate.SessionFactory} mapped to the {@link org.springframework.orm.hibernate5.SessionHolder}

 *  - (Autowired) {@link javax.sql.DataSource} mapped to the {@link org.springframework.jdbc.datasource.ConnectionHolder}

 *  <p>

 * The SessionHolder object itself contains the {@link org.hibernate.Session Session} as well as the {@link org.hibernate.Transaction object.

 * The ConnectionHolder contains the (JDBC) {@link java.sql.Connection Connection} to the database. For every action to do with the

 * transaction object it is required to have both entries present in the resources. Both the session as well as the connection

 * objects must not be null and the corresponding holders must have their 'synchronizedWithTransaction' flag set to true.

 * <p>

 * The default behaviour of the {@link org.springframework.transaction.PlatformTransactionManager PlatformTransactionManager} which in the CDM case is autowired

 * to {@link org.springframework.orm.hibernate5.HibernateTransactionManager HibernateTransactionManager}, is to check these entries

 * when starting a transaction. If this entries do not exist in the resource map then they are created, implying a new session, which

 * is in fact how hibernate implements the default 'session-per-request' pattern internally.

 * <p>

 * Given the above conditions, this class manages long running sessions by providing the following methods,

 * - {@link #bind()} : binds the session owned by this conversation to the resource map

 * - {@link #startTransaction()} : starts a transaction

 * - {@link #commit()} : commits the current transaction, with the option of restarting a new transaction.

 * - {@link #unbind()} : unbinds the session owned by this conversation from the resource map.

 * - {@link #close()} : closes the session owned by this conversation

 * <p>

 * With the exception of {@link #unbind()} (which should be called explicitly), the above sequence must be strictly followed to

 * maintain a consistent session state. Even though it is possible to interweave multiple conversations at the same time, for a

 * specific conversation the above sequence must be followed.

 *

 * @see http://www.hibernate.org/42.html

 *

 * @author n.hoffmann,c.mathew

 * @created 12.03.2009

 * @version 1.0

 */

public class ConversationHolder {

    private static final Logger logger = Logger.getLogger(ConversationHolder.class);

    @Autowired

    private SessionFactory sessionFactory;

    @Autowired

    private DataSource dataSource;

    @Autowired

    private PlatformTransactionManager transactionManager;

    /**

     * The persistence context for this conversation

     */

    private Session longSession = null;

    /**

     * Spring communicates with hibernate sessions via a SessionHolder object

     */

    private SessionHolder sessionHolder = null;

    /**

     * @see TransactionDefinition

     */

    private TransactionDefinition definition;

    /**

     * This conversations transaction

     */

    private TransactionStatus transactionStatus;

    private boolean closed = false;

    /**

     * Simple constructor used by Spring only

     */

    protected ConversationHolder(){

        closed = false;

    }

    public ConversationHolder(DataSource dataSource, SessionFactory sessionFactory,

            PlatformTransactionManager transactionManager) {

        this();

        this.dataSource = dataSource;

        this.sessionFactory = sessionFactory;

        this.transactionManager = transactionManager;

        bind();

        if(TransactionSynchronizationManager.hasResource(getDataSource())){

            TransactionSynchronizationManager.unbindResource(getDataSource());

        }

    }

    /**

     * This method has to be called when starting a new unit-of-work. All required resources are

     * bound so that SessionFactory.getCurrentSession() returns the right session for this conversation

     */

    public void bind() {

        logger.info("Binding resources for ConversationHolder");

        if(TransactionSynchronizationManager.isSynchronizationActive()){

            TransactionSynchronizationManager.clearSynchronization();

        }

        try{

            logger.info("Starting new Synchronization in TransactionSynchronizationManager");

            TransactionSynchronizationManager.initSynchronization();

            if(TransactionSynchronizationManager.hasResource(getSessionFactory())){

                TransactionSynchronizationManager.unbindResource(getSessionFactory());

            }

            logger.info("Binding Session to TransactionSynchronizationManager: Session: " + getSessionHolder());

            TransactionSynchronizationManager.bindResource(getSessionFactory(), getSessionHolder());

        } catch(Exception e){

            logger.error("Error binding resources for session", e);

        }

    }

    /**

     * This method has to be called when suspending the current unit of work. The conversation can be later bound again.

     */

    public void unbind() {

        logger.info("Unbinding resources for ConversationHolder");

        if(TransactionSynchronizationManager.isSynchronizationActive()){

            TransactionSynchronizationManager.clearSynchronization();

        }

        if(isBound()) {

            // unbind the current session.

            // there is no need to bind a new session, since HibernateTransactionManager will create a new one

            // if the resource map does not contain one (ditto for the datasource-to-connection entry).

            TransactionSynchronizationManager.unbindResource(getSessionFactory());

            if(TransactionSynchronizationManager.hasResource(getDataSource())){

                TransactionSynchronizationManager.unbindResource(getDataSource());

            }

        }

    }

    public SessionHolder getSessionHolder(){

        if(this.sessionHolder == null){

            logger.info("Creating new SessionHolder");

            this.sessionHolder = new SessionHolder(getSession());

        }

        return this.sessionHolder;

    }

    /**

     * @return

     */

    private DataSource getDataSource() {

        return this.dataSource;

    }

    /**

     * @return true if this longSession is bound to the session factory.

     */

    public boolean isBound(){

        //return sessionHolder != null && longSession != null && longSession.isConnected();

        SessionHolder currentSessionHolder = (SessionHolder)TransactionSynchronizationManager.getResource(getSessionFactory());

        return longSession != null && currentSessionHolder != null && getSessionFactory().getCurrentSession() == longSession;

    }

    /**

     * Creates an instance of TransactionStatus and binds it to this conversation manager.

     * At the moment we allow only one transaction per conversation holder.

     *

     * @return the transaction status bound to this conversation holder

     */

    public TransactionStatus startTransaction(){

        if (isTransactionActive()){

            logger.warn("We allow only one transaction at the moment but startTransaction " +

                    "was called a second time.\nReturning the transaction already associated with this " +

                    "ConversationManager");

        }else{

            //always safe to remove the datasource-to-connection entry since we

            // know that HibernateTransactionManager will create a new one

            if(TransactionSynchronizationManager.hasResource(getDataSource())){

                TransactionSynchronizationManager.unbindResource(getDataSource());

            }

            transactionStatus = transactionManager.getTransaction(definition);

            logger.info("Transaction started: " + transactionStatus);

        }

        return transactionStatus;

    }

    /**

     * @return if there is a running transaction

     */

    public boolean isTransactionActive(){

        return transactionStatus != null;

    }

    /* (non-Javadoc)

     * @see org.hibernate.Session#evict(java.lang.Object object)

     */

    public void evict(Object object){

        getSession().evict(object);

    }

    /* (non-Javadoc)

     * @see org.hibernate.Session#refresh(java.lang.Object object)

     */

    public void refresh(Object object){

        getSession().refresh(object);

    }

    /* (non-Javadoc)

     * @see org.hibernate.Session#clear()

     */

    public void clear(){

        getSession().clear();

    }

    /**

     * Commit the running transaction.

     */

    public void commit(){

        commit(true);

    }

    /**

     * Commit the running transaction but optionally start a

     * new one right away.

     *

     * @param restartTransaction whether to start a new transaction

     */

    public TransactionStatus commit(boolean restartTransaction){

        if(isTransactionActive()){

            if(getSessionHolder().isRollbackOnly()){

                logger.error("Commiting this session will not work. It has been marked as rollback only.");

            }

            // if a datasource-to-connection entry already exists in the resource map

            // then its setSynchronizedWithTransaction should be true, since hibernate has added

            // this entry.

            // if the datasource-to-connection entry does not exist then we need to create one

            // and explicitly setSynchronizedWithTransaction to true.

            TransactionSynchronizationManager.getResource(getDataSource());

            if(!TransactionSynchronizationManager.hasResource(getDataSource())){

                try {

                    ConnectionHolder ch = new ConnectionHolder(getDataSource().getConnection());

                    ch.setSynchronizedWithTransaction(true);

                    TransactionSynchronizationManager.bindResource(getDataSource(),ch);

                } catch (IllegalStateException e) {

                    // TODO Auto-generated catch block

                    e.printStackTrace();

                } catch (SQLException e) {

                    // TODO Auto-generated catch block

                    e.printStackTrace();

                }

            }

            // commit the changes

            transactionManager.commit(transactionStatus);

			logger.info("Committing  Session: " + getSessionHolder());

            // propagate transaction end

            CdmPostDataChangeObservableListener.getDefault().delayedNotify();

            // Reset the transactionStatus.

            transactionStatus = null;

            // Committing a transaction frees all resources.

            // Since we are in a conversation we directly rebind those resources and start a new transaction

            bind();

            if(restartTransaction){

                return startTransaction();

            }

        }else{

            logger.warn("No active transaction but commit was called");

        }

        return null;

    }

    /**

     * @return the session associated with this conversation manager

     */

    public Session getSession() {

        if(longSession == null){

            longSession = getNewSession();

        }

        return longSession;

    }

    /**

     * @return a new session to be managed by this conversation

     */

    private Session getNewSession() {

        // Interesting: http://stackoverflow.com/questions/3526556/session-connection-deprecated-on-hibernate

        // Also, http://blog-it.hypoport.de/2012/05/10/hibernate-4-migration/

        // This will create a new session which must be explicitly managed by this conversation, which includes

        // binding / unbinding / closing session as well as starting / committing transactions.

        Session session = sessionFactory.openSession();

        session.setFlushMode(FlushMode.COMMIT);

        logger.info("Creating Session: [" + longSession + "]");

        return session;

    }

    /**

     * @return the session factory that is bound to this conversation manager

     */

    public SessionFactory getSessionFactory() {

        return sessionFactory;

    }

    public void delete(Object object){

        this.getSession().delete(object);

    }

    /**

     * Facades Session.lock()

     */

    public void lock(Object persistentObject, LockMode lockMode) {

        getSession().lock(persistentObject, lockMode);

    }

    public void lock(String entityName, Object persistentObject, LockMode lockMode){

        getSession().lock(entityName, persistentObject, lockMode);

    }

    /**

     * @return the definition

     */

    public TransactionDefinition getDefinition() {

        return definition;

    }

    /**

     * @param definition the definition to set

     */

    public void setDefinition(TransactionDefinition definition) {

        this.definition = definition;

    }

    /**

     * Register to get updated after any interaction with the datastore

     */

    public void registerForDataStoreChanges(IConversationEnabled observer) {

        CdmPostDataChangeObservableListener.getDefault().register(observer);

    }

    /**

     * Register to get updated after any interaction with the datastore

     */

    public void unregisterForDataStoreChanges(IConversationEnabled observer) {

        CdmPostDataChangeObservableListener.getDefault().unregister(observer);

    }

    /**

     * Free resources bound to this conversationHolder

     */

    public void close(){

        if(getSession().isOpen()) {

            getSession().close();

            unbind();

        }

        longSession = null;

        sessionHolder = null;

        closed = true;

    }

    public boolean isClosed(){

        return closed;

    }

    public boolean isCompleted(){

        return transactionStatus == null || transactionStatus.isCompleted();

    }

}