对多数据源进行aop声明式事务管理

当在对数据库表进行横向切分(将一个表的数据拆分为到多个数据库中)之后, 在操作数据库的时候需要路由到合适的数据源, 这里我参照了Spring对多数据源的路由处理方式(http://blog.springsource.com/2007/01/23/dynamic-datasource-routing). 具体实现如下.
首先是TransactionManager的配置:

<?xml version="1.0" encoding="gb2312"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
	xmlns:tx="http://www.springframework.org/schema/tx"
	xsi:schemaLocation="
       http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-2.0.xsd
       http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.0.xsd
       http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-2.0.xsd">
	<bean id="db1Tx"
		class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
		<property name="dataSource">
            <ref bean="db1" />
		</property>
	</bean>

	<bean id="db2Tx"
		class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
		<property name="dataSource">
			<ref bean="db2" />
		</property>
	</bean>

	<bean id="dbcTx"
		class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
		<property name="dataSource">
		      <ref bean="dbc" />
		</property>
	</bean>

	<bean id="routingTransactionManager" class="com.mysoft.manager.impl.RoutingTransactionManager">
		<property name="targetTransactionManagers">
			<map value-type="org.springframework.transaction.PlatformTransactionManager">
				<entry key="db1" value-ref="db1Tx" />
				<entry key="db2" value-ref="db2Tx" />
				<entry key="dbc" value-ref="dbcTx" />
			</map>
		</property>
	</bean>

	<!--     配置事务回滚的场景   -->
	<tx:advice id="txAdvice" transaction-manager="routingTransactionManager">
		<tx:attributes>
            		<tx:method name="*" rollback-for="java.lang.Exception"/>
		</tx:attributes>
	</tx:advice>
	
	<!--   指定那些类的哪些方法参与事务   -->
	<aop:config>
        <aop:advisor advice-ref="txAdvice" pointcut="execution(* com.mysoft.manager.Manager1.publish(..))"/>
        <aop:advisor advice-ref="txAdvice" pointcut="execution(* com.mysoft.manager.Manager2.audit(..))"/>
	</aop:config>
</beans>

这里用到了spring的tx和aop标签, 都是spring的参考手册中的典型配置. 当调用指定的packageName.method(..)方法的时候, 将采用事务拦截, 如果在对该方法的调用过程中出现了任何异常将导致事务回滚.

接下来就是路由的问题, 其中RoutingContextHolder类内部使用一个ThreadLocal类用来指定db1, db2, db3等key值, RoutingTransactionManager类则根据当前线程中的key值取得对应的tx.

/**
* 用来存储路由到指定tx的Context
 * 
 * @since 2009-10-28 下午01:54:46
 */
@SuppressWarnings("unchecked")
public class RoutingContextHolder<T> {
    private static final ThreadLocal contextHolder = new ThreadLocal();

    public static <T> void setContext(T context) {
        Validate.notNull(context, "必须指定路由的context");
        contextHolder.set(context);
    }

    public static <T> T getContext() {
        return (T) contextHolder.get();
    }
}

/**
* 根据给定的路由规则来路由到合适的tx类
 * 
 * @since 2009-10-28 下午01:34:11
 * @see RoutingContextHolder
 */
public class RoutingTransactionManager implements PlatformTransactionManager {
    private Map<Object, PlatformTransactionManager> targetTransactionManagers =
            new HashMap<Object, PlatformTransactionManager>();

    /**
     * 根据给定的规则获取指定的tx
     * 
     * @return
     */
    protected PlatformTransactionManager getTargetTransactionManager() {
        Object context = RoutingContextHolder.getContext();
        Validate.notNull(context, "必须指定路由的context");
        return targetTransactionManagers.get(context);
    }

    public void setTargetTransactionManagers(Map<Object, PlatformTransactionManager> targetTransactionManagers) {
        this.targetTransactionManagers = targetTransactionManagers;
    }

    public void commit(TransactionStatus status) throws TransactionException {
        getTargetTransactionManager().commit(status);
    }

    public TransactionStatus getTransaction(TransactionDefinition definition) throws TransactionException {
        return getTargetTransactionManager().getTransaction(definition);
    }

    public void rollback(TransactionStatus status) throws TransactionException {
        getTargetTransactionManager().rollback(status);
    }
}

其调用代码如下:

// 指定tx的路由context
RoutingContextHolder.setContext("db1");
return manager1.publish(item);