TransactionManagerLookupFactory

TransactionManagerLookupFactory.getTransactionManagerLookup根据hibernate.transaction.manager_lookup_class确定TransactionMangerLookup,简要介绍TransactionMangerLookup 

public TransactionManager getTransactionManager(Properties props) throws HibernateException//获取JTA 事务管理器 

public String getUserTransactionName();//获取JTA UserTransaction的JNDI名称 

TransactionManager实现方式可分为通过JNDI查找实例和通过实例化方式; 
如WeblogicTransactionManagerLookup会在JNDI上下文中查找名称为javax.transaction.TransactionManager的事务管理器 
而WebSphereTransactionManagerLookup根据webSphere服务器版本加载对应的class,查找顺序为 
5.1 ->com.ibm.ws.Transaction.TransactionManagerFactory 
5.0->com.ibm.ejs.jts.jta.TransactionManagerFactory 
4.0->com.ibm.ejs.jts.jta.JTSXA 
这些类都实现了getTransactionManager静态方法，通过java反射机制获取事务管理器 
JOnASTransactionManagerLookup加载org.objectweb.jonas_tm.Current，再通过反射机制调用getTransactionManager静态方法 
JOTMTransactionManagerLookup(开源实现，不需要应用服务器提供)加载org.objectweb.jotm.Current 
当然还提供了LocalTransactionManagerLookup，查找spring管理的JTA TransactionManager实现（通过注入LocalSessionFactoryBean的transactionManager属性）。 
//$Id: TransactionManagerLookupFactory.java 11406 2007-04-15 12:52:46Z [e-mail] $
package org.hibernate.transaction;

import java.util.Properties;

import javax.transaction.TransactionManager;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.hibernate.HibernateException;
import org.hibernate.cfg.Environment;
import org.hibernate.util.ReflectHelper;

/**
 * @author Gavin King
 */
public final class TransactionManagerLookupFactory {

	private static final Log log = LogFactory.getLog(TransactionManagerLookupFactory.class);

	private TransactionManagerLookupFactory() {}

	public static final TransactionManager getTransactionManager(Properties props) throws HibernateException {
		log.info("obtaining TransactionManager");
		return getTransactionManagerLookup(props).getTransactionManager(props);
	}

	public static final TransactionManagerLookup getTransactionManagerLookup(Properties props) throws HibernateException {

		String tmLookupClass = props.getProperty(Environment.TRANSACTION_MANAGER_STRATEGY);
		if (tmLookupClass==null) {
			log.info("No TransactionManagerLookup configured (in JTA environment, use of read-write or transactional second-level cache is not recommended)");
			return null;
		}
		else {

			log.info("instantiating TransactionManagerLookup: " + tmLookupClass);

			try {
				TransactionManagerLookup lookup = (TransactionManagerLookup) ReflectHelper.classForName(tmLookupClass).newInstance();
				log.info("instantiated TransactionManagerLookup");
				return lookup;
			}
			catch (Exception e) {
				log.error("Could not instantiate TransactionManagerLookup", e);
				throw new HibernateException("Could not instantiate TransactionManagerLookup '" + tmLookupClass + "'");
			}
		}
	}
}