使用spring配置多个数据源

1.数据源定义

这里以2个c3p0数据库连接池的数据源作为实例。在spring框架下需要加入c3p0的依赖。这里以数据同步为例：

（1）数据库来源的连接池数据源配置

<bean id="dataSourceFrom" class="com.mchange.v2.c3p0.ComboPooledDataSource">
<property name="driverClass" value="${jdbc.driver}" />
<property name="jdbcUrl" value="${jdbc.from.url}" />
<property name="user" value="${jdbc.from.username}" />
<property name="password" value="${jdbc.from.password}" />
<property name="autoCommitOnClose" value="true" />
<property name="checkoutTimeout" value="${cpool.checkoutTimeout}" />
<property name="initialPoolSize" value="${cpool.minPoolSize}" />
<property name="minPoolSize" value="${cpool.minPoolSize}" />
<property name="maxPoolSize" value="${cpool.maxPoolSize}" />
<property name="maxIdleTime" value="${cpool.maxIdleTime}" />
<property name="acquireIncrement" value="${cpool.acquireIncrement}" />
<property name="maxIdleTimeExcessConnections" value="${cpool.maxIdleTimeExcessConnections}" />
</bean>

（2）数据插入库的连接池数据源配置

<bean id="dataSourceTo" class="com.mchange.v2.c3p0.ComboPooledDataSource">
<property name="driverClass" value="${jdbc.driver}" />
<property name="jdbcUrl" value="${jdbc.from.url}" />
<property name="user" value="${jdbc.from.username}" />
<property name="password" value="${jdbc.from.password}" />
<property name="autoCommitOnClose" value="true" />
<property name="checkoutTimeout" value="${cpool.checkoutTimeout}" />
<property name="initialPoolSize" value="${cpool.minPoolSize}" />
<property name="minPoolSize" value="${cpool.minPoolSize}" />
<property name="maxPoolSize" value="${cpool.maxPoolSize}" />
<property name="maxIdleTime" value="${cpool.maxIdleTime}" />
<property name="acquireIncrement" value="${cpool.acquireIncrement}" />
<property name="maxIdleTimeExcessConnections" value="${cpool.maxIdleTimeExcessConnections}" />
</bean>

2.扩展Spring的AbstractRoutingDataSource

AbstractRoutingDataSource中的抽象方法determineCurrentLookupKey是实现数据源的route的核心，这里对该方法进行重写

public class DynamicDataSource extends AbstractRoutingDataSource{

@Override
protected Object determineCurrentLookupKey() {
return DBContextHolder.getDBType();
}
}

其中DBContextHolder是一个线程安全的ThreadLocal，具体代码如下：

public class DBContextHolder{
public static final String DATA_SOURCE_FROM = "dataSourceFrom";
public static final String DATA_SOURCE_TO = "dataSourceTo";

private static final ThreadLocal contextHolder = new ThreadLocal();

public static void setDBType(String dbType) {
contextHolder.set(dbType);
}

public static String getDBType() {
return contextHolder.get();
}

public static void clearDBType() {
contextHolder.remove();
}
}

3.配置动态数据源

将DynamicDataSource加入到spring的配置文件中，同时配置DynamicDataSource的targetDataSource（也就是多个数据源）属性的Map映射

<bean id="dynamicDataSource" class="datasource.DynamicDataSource" >

<property name="targetDataSources">
<map>
<entry value-ref="dataSourceFrom" key="dataSourceFrom"></entry>
<entry value-ref="dataSourceTo" key="dataSourceTo"></entry>
</map>
</property>
<property name="defaultTargetDataSource" ref="dataSourceFrom" />
</bean>

4.使用动态数据源

说明：例子中的DynamicDataSource继承自AbstractRoutingDataSource，而AbstractRoutingDataSource有继承自AbstractDataSource，AbstractDataSource实现了统一的DataSource接口，所以DynamicDataSource同样可以当做一个DataSource来使用

这里使用ibatis作为持久层框架

<bean id="sqlMapClient" class="org.springframework.orm.ibatis.SqlMapClientFactoryBean">
<property name="dataSource" ref="dynamicDataSource<span style="font-family: Arial, Helvetica, sans-serif;">"</span><span style="font-family: Arial, Helvetica, sans-serif;">/>  </span>
<property name="configLocation" value="classpath:com/xxx/xxx/dao/sqlmap/sql-map-config.xml"/>
</bean>
<bean id="userDAO" class="com.xxx.xxx.dao.impl.UserDAO">
<property name="sqlMapClient" ref="sqlMapClient"/>
</bean>

5.事务管理

使用动态数据源的时候，事务管理和单数据源没有差别

<bean id="txManager"
class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
<property name="dataSource" ref="dynamicDataSource" <span style="font-family: Arial, Helvetica, sans-serif;">/>  </span>
</bean>

<tx:advice id="txAdvice" transaction-manager="txManager">
<tx:attributes>
<tx:method name="save*" propagation="REQUIRED" />
<tx:method name="delete*" propagation="REQUIRED" />
<tx:method name="update*" propagation="REQUIRED" />
<tx:method name="select*" propagation="REQUIRED" />
<tx:method name="*" propagation="REQUIRES_NEW"
rollback-for="Exception" />
</tx:attributes>
</tx:advice>

<aop:config proxy-target-class="false">
<aop:advisor pointcut="execution(* com.mycompany.app.service.impl.*.*(..))"
advice-ref="txAdvice" />
</aop:config>

<bean id="sqlMapClient" class="org.springframework.orm.ibatis.SqlMapClientFactoryBean">
<property name="configLocation">  <!-- name 为configLocation或s 不可为其他 -->
<value>sqlMap.xml</value> <!-- 不区分大小写，路径前可加'/' -->
</property>
<!-- dataSource不是必需 -->
<property name="dataSource">
<ref local="dynamicDataSource"<span style="font-family: Arial, Helvetica, sans-serif;"> />  </span>
</property>
</bean>

6.使用

（1）手动控制

ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
BaseDAO dao = (BaseDAO) context.getBean("sqlBaseDAO", BaseDAOImpl.class);

try {
DBContextHolder.setCustomerType(DBContextHolder.DATA_SOURCE_FROM);
System.err.println(dao.select("select count(*) sum from TEST t ").get(0).get("SUM"));
DBContextHolder.setCustomerType(DBContextHolder.DATA_SOURCE_TO);
System.err.println(dao.select("select count(*) sum from TEST t ").get(0).get("SUM"));

} catch (Exception e) {
e.printStackTrace();
}

（2）使用AOP控制

@Aspect
public class DynamicDataSourceAspect {
@Pointcut("execution (public service.impl..*.*(..))")
public void serviceExecution(){}

@Before("serviceExecution()")
public void setDynamicDataSource(JoinPoint jp) {
for(Object o : jp.getArgs()) {
//处理具体的逻辑 ，根据具体的境况CustomerContextHolder.setCustomerType()选取DataSource
}
}
}

7.注意

必须在开启事务之前就切换好数据源，因为事务是和数据源绑定的。

如事务控制设置在service层，那么切换数据源就必须在上一层，也就是Controller层