问题起源:

同一个项目适应多种数据库，基本上是企业应用的常见需求。以往在mybatis中的支持是通过扩展dao而来实现的，参考:

http://code.google.com/p/mybatis/issues/detail?id=21.

问题解决:

而在mybatis3.1.0之后就内在的支持multi-db了，可以在select/update/delete/insert加上databaseId的方式来标识不同的数据库，也可以直接使用属性<if test="_databaseId == 'MySQL'">来判断不同的数据库。那如何在spring中集成mybatis使其支持multi-db的特性呢？在mybatis的官方文档中并没有具体说明，后来通过查看源码，得到主要的spring中的配置项如下:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="locations" value="classpath:datasource.properties"/>
    </bean>

    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="${jdbc.driverClassName}" />
        <property name="url" value="${jdbc.url}" />
        <property name="username" value="${jdbc.usename}" />
        <property name="password" value="${jdbc.password}" />
    </bean>

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

    <bean id="vendorProperties" class="org.springframework.beans.factory.config.PropertiesFactoryBean">
        <property name="properties">
            <props>
                <prop key="SQL Server">sqlserver</prop>
                <prop key="DB2">db2</prop>
                <prop key="Oracle">oracle</prop>
                <prop key="MySQL">mysql</prop>
            </props>
        </property>
    </bean>

    <bean id="databaseIdProvider" class="org.apache.ibatis.mapping.VendorDatabaseIdProvider">
         <property name="properties" ref="vendorProperties"/>
    </bean>

    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
       <property name="mapperLocations" value="classpath*:DYCloudTaskMapper.xml" />
       <property name="dataSource" ref="dataSource" />
       <property name="databaseIdProvider" ref="databaseIdProvider"/>
    </bean>


    <bean id="DYCloudTaskMapper" class="org.mybatis.spring.mapper.MapperFactoryBean">
        <property name="mapperInterface" value="DYCloudTaskMapper" />
        <property name="sqlSessionFactory" ref="sqlSessionFactory" />
    </bean>

</beans>