在仅使用ibatis时，多数据源简直就是梦魇，每多一个数据源就需要多一份sql-map-config配置文件。

在仅使用ibatis时，多数据源简直就是梦魇，每多一个数据源就需要多一份sql-map-config配置文件。

采用spring的AbstractRoutingDataSource就可以简单的解决这个问题。

AbstractRoutingDataSource实现了javax.sql.DataSource接口，因此可以理解为一个虚拟的动态DataSource，在需要的时候根据上下文Context动态决定使用哪个数据源。

Spring+iBatis多数据源的配置

下面是一个完整的配置：

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:jee="http://www.springframework.org/schema/jee"
  xsi:schemaLocation="
   http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
   http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-2.5.xsd">


<!-- ========================= RESOURCE DEFINITIONS ========================= -->

<!-- Main JNDI DataSource for J2EE environments -->
<!-- Refers to the main database, containing product and account data -->
<!-- (see dataAccessContext-local.xml for an alternative) -->
<!--<jee:jndi-lookup id="dataSource" jndi-name="jdbc/jpetstore"/>-->

<!-- Additional JNDI DataSource for J2EE environments -->
<!-- Refers to the order database, containing order data -->
<!-- (see dataAccessContext-local.xml for an alternative) -->
<!--<jee:jndi-lookup id="orderDataSource" jndi-name="jdbc/jpetstore-order"/>-->

<bean id="sysDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
  <property name="driverClassName" value="${jdbcsys.driverClassName}"/>
  <property name="url" value="${jdbcsys.url}"/>
  <property name="username" value="${jdbcsys.username}"/>
  <property name="password" value="${jdbcsys.password}"/>
  <property name="defaultAutoCommit" value="false"/>
</bean>

<bean id="coreDataSource1" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
  <property name="driverClassName" value="${jdbccore1.driverClassName}"/>
  <property name="url" value="${jdbccore1.url}"/>
  <property name="username" value="${jdbccore1.username}"/>
  <property name="password" value="${jdbccore1.password}"/>
  <property name="defaultAutoCommit" value="false"/>
</bean>

<bean id="coreDataSource2" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
  <property name="driverClassName" value="${jdbccore2.driverClassName}"/>
  <property name="url" value="${jdbccore2.url}"/>
  <property name="username" value="${jdbccore2.username}"/>
  <property name="password" value="${jdbccore2.password}"/>
  <property name="defaultAutoCommit" value="false"/>
</bean>

<bean id="dataSource" class="com.bitfone.mvp.bulk.dao.DynamicDataSource">
         <property name="targetDataSources">
            <map key-type="java.lang.String">
               <entry key="SYSDB" value-ref="sysDataSource"/>
               <entry key="COREDB1" value-ref="coreDataSource1"/>
               <entry key="COREDB2" value-ref="coreDataSource2"/>
            </map>
         </property>
         <property name="defaultTargetDataSource" ref="sysDataSource"/>
</bean>


<!-- Transaction manager that delegates to JTA (for a transactional JNDI DataSource) -->
<!-- Necessary here due to the need for distributed transactions across two databases -->
<!-- (see dataAccessContext-local.xml for an alternative) -->
<!--<bean id="transactionManager" class="org.springframework.transaction.jta.JtaTransactionManager"/>-->
<!--<bean id="transactionManager" class="org.springframework.transaction.jta.WebLogicJtaTransactionManager"/>-->

<bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
  <property name="dataSource" ref="dataSource"/>
</bean>

<!-- SqlMap setup for iBATIS Database Layer -->
<bean id="sqlMapClient" class="org.springframework.orm.ibatis.SqlMapClientFactoryBean">
     <!--For release-->
  <property name="configLocation" value="../config/dao/sql-map-config.xml"/>
  <!--For Test-->
  <!--<property name="configLocation" value="classpath:dao/sql-map-config.xml"/>-->
</bean>
</beans>

其核心是DynamicDataSource，代码如下

public class DynamicDataSource extends AbstractRoutingDataSource
{
  protected Object determineCurrentLookupKey()
  {
    return DbContextHolder.getDbType();
  }
}

上下文DbContextHolder为一线程安全的ThreadLocal，如下

public class DbContextHolder
{
  private static final ThreadLocal contextHolder = new ThreadLocal();

  public static void setDbType(String dbType) {
    contextHolder.set(dbType);
  }

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

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