项目中目前用的是Oracle数据库，未来不知道什么时刻确定要切换到MySql数据库，老板让现在支持mysql，未来切换只要改下配置灵活切到Mysql，项目用SpringBoot+Mybatis，配置很简单，网上搜了几个直接照着改老是不成功，试了好几个方法，下面分享下可以用的：

1.mybatis配置两个数据库

iwhalecloud.mysql.datasource.driver=com.mysql.jdbc.Driver
#iwhalecloud.mysql.datasource.url=jdbc:mysql://122.***.9.**:19087/
iwhalecloud.mysql.datasource.url=jdbc:mysql://10.45.**.**:3306/testdb?useUnicode=true&characterEncoding=utf-8&useSSL=false
iwhalecloud.mysql.datasource.username=root
iwhalecloud.mysql.datasource.password=root

iwhalecloud.oracle.datasource.driver=oracle.jdbc.driver.OracleDriver
iwhalecloud.oracle.datasource.url=jdbc:oracle:thin:@10.45.**.**:1521:testDb
iwhalecloud.oracle.datasource.username=root
iwhalecloud.oracle.datasource.password=root

在mybatis配置文件配置两个数据源，红色字体是今后我们切换数据库要改动的地方

<bean id="datasource1" parent="parentDataSource" init-method="init" destroy-method="close">
    <property name="url" value="${iwhalecloud.mysql.datasource.url}"/>
    <property name="username" value="${iwhalecloud.mysql.datasource.username}"/>
    <property name="password" value="${iwhalecloud.mysql.datasource.password}"/>
    <property name="driverClassName" value="${iwhalecloud.mysql.datasource.driver}"/>
</bean>

<bean id="datasource2" parent="parentOracleDataSource" init-method="init" destroy-method="close">
    <property name="url" value="${iwhalecloud.oracle.datasource.url}"/>
    <property name="username" value="${iwhalecloud.oracle.datasource.username}"/>
    <property name="password" value="${iwhalecloud.oracle.datasource.password}"/>
    <property name="driverClassName" value="${iwhalecloud.oracle.datasource.driver}"/>
</bean>

<bean id="dataSource" class="com.iwhalecloud.simulation.common.bean.MultiDataSource">
    <property name="targetDataSources">
        <map key-type="java.lang.String">
            <entry value-ref="datasource2" key="oracle"/>
        </map>
    </property>
    <property name="defaultTargetDataSource" ref="datasource2"/>
</bean>

2.配置databaseIdProvider，红色地方是引用下方配置

<bean id="sqlSessionFactory"
      class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource"/>
    <property name="vfs" value="org.mybatis.spring.boot.autoconfigure.SpringBootVFS"/>
    <!-- 自动扫描Mapping.xml文件 -->
    <property name="mapperLocations">
        <array>
            <value>classpath*:/mapper/*.xml</value>
        </array>
    </property>
    <property name="databaseIdProvider" ref="databaseIdProvider" />
    <property name="configLocation" value="classpath:mybatis/mybatisConfig.xml"/>
</bean>

<bean id="vendorProperties"
      class="org.springframework.beans.factory.config.PropertiesFactoryBean">
    <property name="properties">
        <props>
            <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>

3.使用：如果只是简单的增删改查，没有用到函数，一套sql可以共用，不必加databaseId，如果负载sql需要区分

<select id="qryAllUserInfo" databaseId="oracle" parameterType="****" >
    select * from sys_user
</select>

<select id="qryAllUserInfo" databaseId="mysql" parameterType="****" >

    select * from sys_user

</select>