自由飛翔

適用范圍：適合SSH架構訪問多個數據庫，數據庫的類型和表結構不必相同，且沒有跨庫事務的情況（跨庫事務最好用分布式事務處理）。

<!-- Hibernate SessionFactorys -->
<bean id="aSessionFactory"
   class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
   <property name="dataSource">
    <ref local="aDataSource" />
   </property>
   <property name="mappingResources">
    <list>
     <value>
      .hbm.xml文件
     </value>
    </list>
   </property>
   <property name="hibernateProperties">
    <props>
     <prop key="hibernate.dialect">
      ${ahibernate.dialect}
     </prop>
     <prop key="hibernate.show_sql">true</prop>
     <prop key="format_sql">true</prop>
    </props>
   </property>
</bean>

<bean id="bSessionFactory"
   class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
   <property name="dataSource">
    <ref local="bDataSource" />
   </property>
   <property name="mappingResources">
    <list>
     <value>
      .hbm.xml文件
     </value>
    </list>
   </property>
   <property name="hibernateProperties">
    <props>
     <prop key="hibernate.dialect">
      ${bhibernate.dialect}
     </prop>
     <prop key="hibernate.show_sql">true</prop>
     <prop key="format_sql">true</prop>
    </props>
   </property>
</bean>

<bean id="cSessionFactory"
   class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">
   <property name="dataSource">
    <ref local="cDataSource" />
   </property>
   <property name="mappingResources">
    <list>
     <value>
       .hbm.xml文件
     </value>
    </list>
   </property>
   <property name="hibernateProperties">
    <props>
     <prop key="hibernate.dialect">
      ${chibernate.dialect}
     </prop>
     <prop key="hibernate.show_sql">true</prop>
     <prop key="format_sql">true</prop>
    </props>
   </property>
</bean>

<bean id="sessionFactory" class="com.cintel.dcp.datasource.MultiSessionFactory">
   <property name="sessionFactory"><ref local="aSessionFactory"/></property>
</bean>
注意：最后一個com.cintel.dcp.datasource.MultiSessionFactory要自己實現，它實現了SessionFactory接口和ApplicationContext接口，如下：
package com.cintel.dcp.datasource;

import java.io.Serializable;
import java.sql.Connection;
import java.util.Map;
import java.util.Set;

import javax.naming.NamingException;
import javax.naming.Reference;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.hibernate.HibernateException;
import org.hibernate.Interceptor;
import org.hibernate.SessionFactory;
import org.hibernate.StatelessSession;
import org.hibernate.classic.Session;
import org.hibernate.engine.FilterDefinition;
import org.hibernate.metadata.ClassMetadata;
import org.hibernate.metadata.CollectionMetadata;
import org.hibernate.stat.Statistics;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

public class MultiSessionFactory implements SessionFactory, ApplicationContextAware {
private static final long serialVersionUID = 2064557324203496378L;
private static final Log log = LogFactory.getLog(MultiSessionFactory.class);
private ApplicationContext applicationContext = null;
private SessionFactory sessionFactory = null;

public ApplicationContext getApplicationContext() {
   return applicationContext;
}

public void setApplicationContext(ApplicationContext applicationContext) {
   this.applicationContext = applicationContext;
}

public SessionFactory getSessionFactory(String sessionFactoryName) {
   log.debug("sessionFactoryName:"+sessionFactoryName);
   try{
    if(sessionFactoryName==null||sessionFactoryName.equals("")){
     return sessionFactory;
    }
    return (SessionFactory)this.getApplicationContext().getBean(sessionFactoryName);
   }catch(NoSuchBeanDefinitionException ex){
    throw new RuntimeException("There is not the sessionFactory <name:"+sessionFactoryName+"> in the applicationContext!");
   }
}

public SessionFactory getSessionFactory() {
   String sessionFactoryName = CustomerContextHolder.getCustomerType();
   return getSessionFactory(sessionFactoryName);
}

public void setSessionFactory(SessionFactory sessionFactory) {
   this.sessionFactory = sessionFactory;
}


/* (non-Javadoc)
* @see org.hibernate.SessionFactory#close()
*/
public void close() throws HibernateException {
   getSessionFactory().close();
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#evict(java.lang.Class)
*/
public void evict(Class persistentClass) throws HibernateException {
   getSessionFactory().evict(persistentClass);
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#evict(java.lang.Class, java.io.Serializable)
*/
public void evict(Class persistentClass, Serializable id) throws HibernateException {
   getSessionFactory().evict(persistentClass, id);
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#evictCollection(java.lang.String)
*/
public void evictCollection(String roleName) throws HibernateException {
   getSessionFactory().evictCollection(roleName);
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#evictCollection(java.lang.String, java.io.Serializable)
*/
public void evictCollection(String roleName, Serializable id) throws HibernateException {
   getSessionFactory().evictCollection(roleName, id);
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#evictEntity(java.lang.String)
*/
public void evictEntity(String entityName) throws HibernateException {
   getSessionFactory().evictEntity(entityName);
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#evictEntity(java.lang.String, java.io.Serializable)
*/
public void evictEntity(String entityName, Serializable id) throws HibernateException {
   getSessionFactory().evictEntity(entityName, id);
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#evictQueries()
*/
public void evictQueries() throws HibernateException {
   getSessionFactory().evictQueries();
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#evictQueries(java.lang.String)
*/
public void evictQueries(String cacheRegion) throws HibernateException {
   getSessionFactory().evictQueries(cacheRegion);
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#getAllClassMetadata()
*/
public Map getAllClassMetadata() throws HibernateException {
   return getSessionFactory().getAllClassMetadata();
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#getAllCollectionMetadata()
*/
public Map getAllCollectionMetadata() throws HibernateException {
   return getSessionFactory().getAllCollectionMetadata();
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#getClassMetadata(java.lang.Class)
*/
public ClassMetadata getClassMetadata(Class persistentClass) throws HibernateException {
   return getSessionFactory().getClassMetadata(persistentClass);
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#getClassMetadata(java.lang.String)
*/
public ClassMetadata getClassMetadata(String entityName) throws HibernateException {
   return getSessionFactory().getClassMetadata(entityName);
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#getCollectionMetadata(java.lang.String)
*/
public CollectionMetadata getCollectionMetadata(String roleName) throws HibernateException {
   return getSessionFactory().getCollectionMetadata(roleName);
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#getCurrentSession()
*/
public Session getCurrentSession() throws HibernateException {
   return getSessionFactory().getCurrentSession();
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#getDefinedFilterNames()
*/
public Set getDefinedFilterNames() {
   return getSessionFactory().getDefinedFilterNames();
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#getFilterDefinition(java.lang.String)
*/
public FilterDefinition getFilterDefinition(String filterName) throws HibernateException {
   return getSessionFactory().getFilterDefinition(filterName);
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#getStatistics()
*/
public Statistics getStatistics() {
   return getSessionFactory().getStatistics();
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#isClosed()
*/
public boolean isClosed() {
   return getSessionFactory().isClosed();
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#openSession()
*/
public Session openSession() throws HibernateException {
   return getSessionFactory().openSession();
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#openSession(java.sql.Connection)
*/
public Session openSession(Connection connection) {
   return getSessionFactory().openSession(connection);
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#openSession(org.hibernate.Interceptor)
*/
public Session openSession(Interceptor interceptor) throws HibernateException {
   return getSessionFactory().openSession(interceptor);
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#openSession(java.sql.Connection, org.hibernate.Interceptor)
*/
public Session openSession(Connection connection, Interceptor interceptor) {
   return getSessionFactory().openSession(connection, interceptor);
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#openStatelessSession()
*/
public StatelessSession openStatelessSession() {
   return getSessionFactory().openStatelessSession();
}
/* (non-Javadoc)
* @see org.hibernate.SessionFactory#openStatelessSession(java.sql.Connection)
*/
public StatelessSession openStatelessSession(Connection connection) {
   return getSessionFactory().openStatelessSession(connection);
}
/* (non-Javadoc)
* @see javax.naming.Referenceable#getReference()
*/
public Reference getReference() throws NamingException {
   return getSessionFactory().getReference();
}
}

然后我用一個常量類來標識sessionFactory
public class DynamicDataSourceType {
public static final String A= "aSessionFactory";
public static final String B= "bSessionFactory";
public static final String C= "cSessionFactory";
}

最后一個關鍵類：用來存放當前正在使用的sessionFactory
public class CustomerContextHolder {

private static final ThreadLocal contextHolder = new ThreadLocal();

public static void setCustomerType(String customerType) {
   Assert.notNull(customerType, "customerType cannot be null");
   contextHolder.set(customerType);
}

public static String getCustomerType() {
   return (String) contextHolder.get();
}

public static void clearCustomerType() {
   contextHolder.remove();
}
}

可以在action、service、dao中進行數據庫切換，切換方式：
CustomerContextHolder.setCustomerType(DynamicDataSourceType.A);

以上思路來自javaEye論壇的一個高手，在此標識感謝