随着业务增长，一般会对数据进行垂直切分与水平切分， 一般会有一个应用对应多个数据源的需求。

本文基于Spring 3.1.1.RELEASE 和 iBatis 实现多数据源配置， 有以下两种方法。

配置多个SqlMapClientTemplate

一个SqlMapClientTemplate 对应一个数据源

  <!-- global 数据源配置 -->
  <bean id="globalDataSource" class="com.alibaba.druid.pool.DruidDataSource"
        init-method="init" destroy-method="close">
    <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
    <property name="url" value="${redisa.database.global.url}"/>
    <property name="username" value="${redisa.database.global.username}"/>
    <property name="password" value="${redisa.database.global.password}" />
  </bean>
  <bean id="globalSqlMapClientTemplate" class="org.springframework.orm.ibatis.SqlMapClientTemplate">
    <property name="sqlMapClient">
      <bean class="org.springframework.orm.ibatis.SqlMapClientFactoryBean">
        <property name="configLocation">
          <value>classpath:ibatis/sqlmap-config.xml</value>
        </property>
        <property name="dataSource">
          <ref local="globalDataSource"/>
        </property>
      </bean>
    </property>
    <property name="dataSource">
      <ref local="globalDataSource"/>
    </property>
  </bean>
  <!-- // -->

  <!-- region 数据源配置 -->
  <bean id="regionDataSource" class="com.alibaba.druid.pool.DruidDataSource"
        init-method="init" destroy-method="close">
    <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
    <property name="url" value="${redisa.database.region.url}"/>
    <property name="username" value="${redisa.database.region.username}"/>
    <property name="password" value="${redisa.database.region.password}" />
  </bean>

  <bean id="regionSqlMapClientTemplate" class="org.springframework.orm.ibatis.SqlMapClientTemplate">
    <property name="sqlMapClient">
      <bean class="org.springframework.orm.ibatis.SqlMapClientFactoryBean">
        <property name="configLocation">
          <value>classpath:ibatis/sqlmap-config.xml</value>
        </property>
        <property name="dataSource">
          <ref local="regionDataSource"/>
        </property>
      </bean>
    </property>
    <property name="dataSource">
      <ref local="regionDataSource"/>
    </property>
  </bean>

设置好 sqlMapClientTemplate 后，在不同的DAO 中引用对应的sqlMapClientTemplate

  <bean id="redisaConfigDao" class="com.aliyun.redisa.phoenix.dao.impl.RedisaConfigDaoImpl">
    <property name="sqlMapClientTemplate" ref="globalSqlMapClientTemplate" />
  </bean>

  <bean id="redisaInstanceDAO" class="com.aliyun.redisa.phoenix.dao.impl.RedisaInstanceDAOImpl">
    <property name="regionSqlMapClientTemplate" ref="regionSqlMapClientTemplate" />
  </bean>

重写AbstractRoutingDataSource 的determineCurrentLookupKey 方法

• 使用ThreadLocal 来保存当前线程使用的数据源

public class DynamicDataSourceHolder {
    /**
     * 数据源标识保存在线程变量中，避免多线程操作数据源时互相干扰
     */
    private static final ThreadLocal<String> THREAD_DATA_SOURCE = new ThreadLocal<String>();

    public static String getDataSource() {
        return THREAD_DATA_SOURCE.get();
    }

    public static void setDataSource(String dataSource) {
        THREAD_DATA_SOURCE.set(dataSource);
    }

    public static void clearDataSource() {
        THREAD_DATA_SOURCE.remove();
    }
}

• 编写DynamicDataSource.java 类重写AbstractRoutingDataSource 的determineCurrentLookupKey 方法

public class DynamicDataSource extends AbstractRoutingDataSource {
    @Override
    protected Object determineCurrentLookupKey() {
        // 从自定义的位置获取数据源标识
        return DynamicDataSourceHolder.getDataSource();
    }
}

• 配置数据源

  <!-- apsaradb phoenix global config begin -->
  <bean id="globalDataSource" class="com.alibaba.druid.pool.DruidDataSource"
        init-method="init" destroy-method="close">
    <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
    <property name="url" value="${adb.database.global.url}"/>
    <property name="username" value="${adb.database.global.username}"/>
    <property name="password" value="${adb.database.global.password}"/>
  </bean>
  <!-- apsaradb phoenix global config end-->

  <!-- product database begin-->
  <!-- rds database config -->
  <bean id="rdsDataSource" class="com.alibaba.druid.pool.DruidDataSource"
        init-method="init" destroy-method="close">
    <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
    <property name="url" value="${rds.database.url}"/>
    <property name="username" value="${rds.database.username}"/>
    <property name="password" value="${rds.database.password}"/>
  </bean>
  <!-- product datasource end-->

  <!-- multi datasource config -->
  <util:map id="dataSources">
    <!-- 指定lookupKey和与之对应的数据源 -->
    <entry key="global" value-ref="globalDataSource" />
    <entry key="rds" value-ref="rdsDataSource" />
  </util:map>
  <bean id="dataSourceLookup" class="org.springframework.jdbc.datasource.lookup.MapDataSourceLookup">
    <constructor-arg ref="dataSources"/>
  </bean>
  <bean id="dynamicDataSource" class="com.aliyun.adb.dao.datasource.DynamicDataSource">
    <property name="targetDataSources" ref="dataSources"/>
    <!-- 这里可以指定默认的数据源 -->
    <property name="defaultTargetDataSource" ref="globalDataSource" />
    <property name="dataSourceLookup" ref="dataSourceLookup" />
  </bean>
  <!-- multi datasource config end-->

  <!-- sqlMapClient config-->
  <bean id="sqlMapClientFactory" class="org.springframework.orm.ibatis.SqlMapClientFactoryBean">
    <property name="dataSource" ref="dynamicDataSource"/>
    <property name="configLocation" value="classpath:ibatis/sqlmap-config.xml"/>
  </bean>
  <bean id="sqlMapClientTemplate" class="org.springframework.orm.ibatis.SqlMapClientTemplate">
    <property name="sqlMapClient" ref="sqlMapClientFactory" />
    <property name="dataSource">
      <ref local="dynamicDataSource"/>
    </property>
  </bean>
  <!-- -->

• 在各个DAO引用sqlMapClientTemplate

  <bean id="rdsInstanceDao" class="com.aliyun.adb.dao.impl.RdsInstanceDAOImpl">
    <property name="sqlMapClientTemplate" ref="sqlMapClientTemplate" />
  </bean>

• 在使用DAO 来进行查询之前设置成应该使用的数据源

    public InstanceDO getByInstanceId(NewBaseRequest request) {
        DynamicDataSourceHolder.setDataSource("rds");

        InstanceDO instance = instanceDAO.getByInstanceId(request.getDbInstanceId());
        
        return instance;
    }