spring+mybaits多数据源使用

一、在利用spring管理mybatis时可以同时配置多个数据源，并且数据源可以随时切换，但在多线程中多数据源的事务需要一定的配置。

多数据源配置：

<bean id="postgresqlDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
<property name="driverClassName" value="${jdbc.postgresql.driver}"/>
<property name="url" value="${jdbc.postgresql.url}"/>
<property name="username" value="${jdbc.postgresql.username}"/>
<property name="password" value="${jdbc.postgresql.password}"/>
<property name="initialSize" value="${jdbc.initialSize}"/>
<property name="minIdle" value="${jdbc.minIdle}"/>
<property name="maxIdle" value="${jdbc.maxIdle}"/>
<property name="maxActive" value="${jdbc.maxActive}"/>
<property name="maxWait" value="${jdbc.maxWait}"/>
<property name="defaultAutoCommit" value="${jdbc.defaultAutoCommit}"/>
<property name="removeAbandoned" value="${jdbc.removeAbandoned}"/>
<property name="removeAbandonedTimeout" value="${jdbc.removeAbandonedTimeout}"/>
<property name="testWhileIdle" value="${jdbc.testWhileIdle}"/>
<property name="timeBetweenEvictionRunsMillis" value="${jdbc.timeBetweenEvictionRunsMillis}"/>
<property name="numTestsPerEvictionRun" value="${jdbc.numTestsPerEvictionRun}"/>
<property name="minEvictableIdleTimeMillis" value="${jdbc.minEvictableIdleTimeMillis}"/>
</bean>
<bean id="oracleDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
<property name="driverClassName" value="${jdbc.oracle.driver}"/>
<property name="url" value="${jdbc.oracle.url}"/>
<property name="username" value="${jdbc.oracle.username}"/>
<property name="password" value="${jdbc.oracle.password}"/>
<property name="initialSize" value="${jdbc.initialSize}"/>
<property name="minIdle" value="${jdbc.minIdle}"/>
<property name="maxIdle" value="${jdbc.maxIdle}"/>
<property name="maxActive" value="${jdbc.maxActive}"/>
<property name="maxWait" value="${jdbc.maxWait}"/>
<property name="defaultAutoCommit" value="${jdbc.defaultAutoCommit}"/>
<property name="removeAbandoned" value="${jdbc.removeAbandoned}"/>
<property name="removeAbandonedTimeout" value="${jdbc.removeAbandonedTimeout}"/>
<property name="testWhileIdle" value="${jdbc.testWhileIdle}"/>
<property name="timeBetweenEvictionRunsMillis" value="${jdbc.timeBetweenEvictionRunsMillis}"/>
<property name="numTestsPerEvictionRun" value="${jdbc.numTestsPerEvictionRun}"/>
<property name="minEvictableIdleTimeMillis" value="${jdbc.minEvictableIdleTimeMillis}"/>
</bean>
<bean id="mysqlDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
<property name="driverClassName" value="${jdbc.mysql.driver}"/>
<property name="url" value="${jdbc.mysql.url}"/>
<property name="username" value="${jdbc.mysql.username}"/>
<property name="password" value="${jdbc.mysql.password}"/>
<property name="initialSize" value="${jdbc.initialSize}"/>
<property name="minIdle" value="${jdbc.minIdle}"/>
<property name="maxIdle" value="${jdbc.maxIdle}"/>
<property name="maxActive" value="${jdbc.maxActive}"/>
<property name="maxWait" value="${jdbc.maxWait}"/>
<property name="defaultAutoCommit" value="${jdbc.defaultAutoCommit}"/>
<property name="removeAbandoned" value="${jdbc.removeAbandoned}"/>
<property name="removeAbandonedTimeout" value="${jdbc.removeAbandonedTimeout}"/>
<property name="testWhileIdle" value="${jdbc.testWhileIdle}"/>
<property name="timeBetweenEvictionRunsMillis" value="${jdbc.timeBetweenEvictionRunsMillis}"/>
<property name="numTestsPerEvictionRun" value="${jdbc.numTestsPerEvictionRun}"/>
<property name="minEvictableIdleTimeMillis" value="${jdbc.minEvictableIdleTimeMillis}"/>
</bean>

<bean id="dataSource" class="orm.user.datasource.DataSource">
<property name="targetDataSources">
<map key-type="java.lang.String">
<entry key="postgres" value-ref="postgresqlDataSource" />
<entry key="oracle" value-ref="oracleDataSource" />
<entry key="mysql" value-ref="mysqlDataSource"></entry>
</map>
</property>
<property name="defaultTargetDataSource" ref="postgresqlDataSource"></property>
</bean>

<!-- mybatis 配置 -->
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="dataSource" ref="dataSource" />
<property name="databaseIdProvider" ref="databaseIdProvider" />
<property name="configLocation" value="classpath:mybatis-config.xml" />

</bean>

<bean id="sqlSessionTemplate" class="org.mybatis.spring.SqlSessionTemplate">
<constructor-arg ref="sqlSessionFactory" />
</bean>

二、多数据源存在的问题是各个数据库类型直接的sql语句并不相同，比如mysql和postgresql的分页语句就不同，mybatis提供了一种简单的方法，首先你需要根据数据库类型写对应的sql语句，mybatis的VendorDatabaseIdProvider会根据数据源的类型选择对应的sql语句进行执行。

如下配置：

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

三、在mybatis的mapper配置文件中进行 "_databaseId" 判断，是哪种数据源类型就使用相对应的sql语句

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="orm.user">
<select id="getUser"  resultType="orm.user.entity.User">

<if test="_databaseId == 'mysql'">
select * from tbl_user  order by id desc limit 5
</if>

<if test="_databaseId == 'postgresql'">
select * from tbl_user  order by id desc  limit 1 offset 0
</if>

</select>

</mapper>