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>