專案中我們經常會遇到多資料來源的問題，尤其是資料同步或定時任務等專案更是如此。多資料來源讓人最頭痛的，不是配置多個數據源，而是如何能靈活動態的切換資料來源。例如在一個spring和hibernate的框架的專案中，我們在spring配置中往往是配置一個dataSource來連線資料庫，然後繫結給sessionFactory，在dao層程式碼中再指定sessionFactory來進行資料庫操作。

正如上圖所示，每一塊都是指定綁死的，如果是多個數據源，也只能是下圖中那種方式。

可看出在Dao層程式碼中寫死了兩個SessionFactory，這樣日後如果再多一個數據源，還要改程式碼新增一個SessionFactory，顯然這並不符合開閉原則。

那麼正確的做法應該是

1. applicationContext.xml如下

<span style="font-size:12px;"><?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
	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-3.0.xsd
       	   http://www.springframework.org/schema/context
           http://www.springframework.org/schema/context/spring-context-3.0.xsd
           http://www.springframework.org/schema/tx
     http://www.springframework.org/schema/tx/spring-tx-3.0.xsd
           http://www.springframework.org/schema/aop
           http://www.springframework.org/schema/aop/spring-aop-3.0.xsd">
           
    <context:annotation-config />
    <!-- 隱式地向 Spring 容器註冊
    AutowiredAnnotationBeanPostProcessor、
    CommonAnnotationBeanPostProcessor、
    PersistenceAnnotationBeanPostProcessor、
    RequiredAnnotationBeanPostProcessor  -->
	<context:component-scan base-package="com.saleSystem,com.interfaces" /><!-- 掃描包中的所有Bean,配置掃描包路徑選項 -->
	<tx:annotation-driven transaction-manager="txManager" /><
 
[email protected]這個註解進行的驅動，這是基於註解的方式使用事務配置宣告 -->
	<bean id="propertyConfigurer"
		class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
		<property name="locations">
			<value>classpath:app/jdbc.properties</value>
		</property>
	</bean>

	<bean id="parentDataSource" class="org.apache.commons.dbcp.BasicDataSource">
		<property name="driverClassName" value="${jdbc.driverClassName}" />
		<property name="username" value="${jdbc.username}" />
		<property name="password" value="${jdbc.password}" />		
        <property name="initialSize" value="5" />
        <property name="maxActive" value="50" />
        <property name="maxIdle" value="50" />
        <property name="minIdle" value="0" />
        <property name="maxWait" value="6000" />
        <property name="timeBetweenEvictionRunsMillis" value="60000" />
        <property name="minEvictableIdleTimeMillis" value="25200000" />
	</bean>
	
	<bean id="adminDataSource" parent="parentDataSource">  
        <property name="url" value="${jdbc.url}" />
    </bean>  
       
    <bean id="logDataSource" parent="parentDataSource">  
        <property name="url" value="${log.url}" />
    </bean>  	
	<bean id="dataSource" class="com.datasource.DynamicDataSource">  
       <property name="targetDataSources">  
          <map key-type="java.lang.String">  
             <entry key="logDataSource" value-ref="logDataSource"/>  
          </map>  
       </property>  
       <property name="defaultTargetDataSource" ref="adminDataSource"/>  
    </bean>  
	<bean id="sessionFactory"
		class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean">
		<property name="dataSource" ref="dataSource" />

		<!-- hibernate 方言 -->
		<property name="hibernateProperties">
			<props>
				<prop key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop>
				<prop key="hibernate.show_sql">true</prop>
				<prop key="javax.persistence.validation.mode">none</prop>
				<prop key="hibernate.format_sql">false</prop>
				<prop key="hibernate.hbm2ddl.auto">validate</prop>
			</props>
		</property>

		<property name="mappingDirectoryLocations">
			<list>
				<value>
					classpath:hibernate
				</value>
			</list>
		</property>
	</bean>
	
	<bean id="hibernateTemplate" class="org.springframework.orm.hibernate3.HibernateTemplate">
		<property name="sessionFactory" ref="sessionFactory"></property>
	</bean>
	
	<bean id="txManager"
		class="org.springframework.orm.hibernate3.HibernateTransactionManager">
		<property name="sessionFactory" ref="sessionFactory" />
	</bean>

	<!-- 面向切面控制權限 -->
	 <aop:config>
		<aop:pointcut expression="execution(public * com.saleSystem.services..*.* (..))"
			id="bussinessService" />
		<aop:advisor pointcut-ref="bussinessService" advice-ref="txAdvice" />
	</aop:config>

	<!-- 諫言 -->
	<!-- 事務 -->
	<tx:advice id="txAdvice" transaction-manager="txManager">
		<tx:attributes>
			<tx:method name="get*" read-only="true" /><!--以get開頭的方法只能從資料庫中讀取資料  -->
			<tx:method name="find*" read-only="true" />
			<tx:method name="query*" read-only="true"/>
            <tx:method name="load*" propagation="SUPPORTS" />
            <tx:method name="search*" propagation="SUPPORTS" />
            <tx:method name="datagrid*" propagation="SUPPORTS" />
            
			<tx:method name="add*" propagation="REQUIRED" rollback-for="Exception"/><!--以add開頭的方法能對資料庫進行查詢、新增、刪除、編輯1  -->
            <tx:method name="edit*" propagation="REQUIRED" rollback-for="Exception"/>
			<tx:method name="save*" propagation="REQUIRED" rollback-for="Exception" />
			<tx:method name="update*" propagation="REQUIRED" rollback-for="Exception"/>
			<tx:method name="remove*" propagation="REQUIRED" rollback-for="Exception"/>
			<tx:method name="delete*" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="modify*" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="repair" propagation="REQUIRED" rollback-for="Exception"/>
           <tx:method name="deleteAndRepair" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="put*" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="restart*" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="stop*" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="change*" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="check*" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="start*" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="porkDiv" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="send*" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="porkRej" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="porkPdtRej" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="loginTimeAdd" propagation="REQUIRED" rollback-for="Exception"/>   
            <tx:method name="productSaleBySaleIdAndType" propagation="REQUIRED" rollback-for="Exception"/>
            <tx:method name="sale*" propagation="REQUIRED"/>      
		</tx:attributes>
	</tx:advice>
</beans></span>
 

2. DynamicDataSource.java

import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;

public class DynamicDataSource extends AbstractRoutingDataSource {

	protected Object determineCurrentLookupKey() {
		return CustomerContextHolder.getCustomerType();
	}

}

3.CustomerContextHolder.java

public class CustomerContextHolder {
	private static final ThreadLocal contextHolder = new ThreadLocal();

	public static void setCustomerType(String customerType) {
		contextHolder.set(customerType);
	}

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

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

}

 CustomerContextHolder.setCustomerType(DataSourceMap.Admin);//設定資料來源

但是實際運用中，無需再選擇資料來源，Spring會自動根據不同的Model找到相應的資料來源。

另外AbstractRoutingDataSource類也可以實現主從表讀寫分離，目前還未嘗試，但是通過AOP+Annotation即可。