/*
 * Copyright 2002-2004 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
 * 
 *      http://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.hibernate;

import java.util.Properties;

import javax.transaction.TransactionManager;

import net.sf.hibernate.transaction.TransactionManagerLookup;

/**
 * Implementation of Hibernate's TransactionManagerLookup interface that
 * returns a Spring-managed JTA TransactionManager, determined by
 * LocalSessionFactoryBean's "transactionManager" property.
 *
 * <p>The main advantage of this TransactionManagerLookup is that it avoids
 * double configuration of JTA specifics. A single TransactionManager bean can
 * be used for both JtaTransactionManager and LocalSessionFactoryBean, with no
 * JTA setup in Hibernate configuration.
 *
 * <p>Alternatively, use Hibernate's own TransactionManagerLookup implementations:
 * Spring's JtaTransactionManager only requires a TransactionManager for suspending
 * and resuming transactions, so you might not need to apply such special Spring
 * configuration at all.
 *
 * @author Juergen Hoeller
 * @since 21.01.2004
 * @see LocalSessionFactoryBean#setJtaTransactionManager
 * @see org.springframework.transaction.jta.JtaTransactionManager#setTransactionManager
 */
public class LocalTransactionManagerLookup implements TransactionManagerLookup {

	/**
	 * This will hold the TransactionManager to use for the currently configured
	 * Hibernate SessionFactory. It will be set just before initialization
	 * of the respective SessionFactory, and reset immediately afterwards.
	 */
	protected static ThreadLocal configTimeTransactionManagerHolder = new ThreadLocal();

	private final TransactionManager transactionManager;

	public LocalTransactionManagerLookup() {
		TransactionManager tm = (TransactionManager) configTimeTransactionManagerHolder.get();
		// absolutely needs thread-bound DataSource to initialize
		if (tm == null) {
			throw new IllegalStateException("No TransactionManager found - transactionManager property must be set on LocalSessionFactoryBean");
		}
		this.transactionManager = tm;
	}

	public TransactionManager getTransactionManager(Properties props) {
		return transactionManager;
	}

	public String getUserTransactionName() {
		return null;
	}

}