项目中我们经常会遇到多数据源的问题，尤其是数据同步或定时任务等项目更是如此。多数据源让人最头痛的，不是配置多个数据源，而是如何能灵活动态的切换数据源。例如在一个spring和hibernate的框架的项目中，我们在spring配置中往往是配置一个dataSource来连接数据库，然后绑定给sessionFactory，在dao层代码中再指定sessionFactory来进行数据库操作。

正如上图所示，每一块都是指定绑死的，如果是多个数据源，也只能是下图中那种方式。

可看出在Dao层代码中写死了两个SessionFactory，这样日后如果再多一个数据源，还要改代码添加一个SessionFactory，显然这并不符合开闭原则。

那么正确的做法应该是

代码如下：

1. applicationContext.xml

<?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:aop="http://www.springframework.org/schema/aop"

	xmlns:cache="http://www.springframework.org/schema/cache"

	xmlns:context="http://www.springframework.org/schema/context"

	xmlns:jdbc="http://www.springframework.org/schema/jdbc" xmlns:jee="http://www.springframework.org/schema/jee"

	xmlns:jms="http://www.springframework.org/schema/jms" xmlns:lang="http://www.springframework.org/schema/lang"

	xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:oxm="http://www.springframework.org/schema/oxm"

	xmlns:p="http://www.springframework.org/schema/p" xmlns:task="http://www.springframework.org/schema/task"

	xmlns:tx="http://www.springframework.org/schema/tx" xmlns:util="http://www.springframework.org/schema/util"

	xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd

	http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.1.xsd

   	http://www.springframework.org/schema/cache http://www.springframework.org/schema/cache/spring-cache-3.1.xsd

    http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.1.xsd

    http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc-3.1.xsd

    http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee-3.1.xsd

    http://www.springframework.org/schema/jms http://www.springframework.org/schema/jms/spring-jms-3.1.xsd

  	http://www.springframework.org/schema/lang http://www.springframework.org/schema/lang/spring-lang-3.1.xsd

   	http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.1.xsd

  	http://www.springframework.org/schema/oxm http://www.springframework.org/schema/oxm/spring-oxm-3.1.xsd

 	http://www.springframework.org/schema/task http://www.springframework.org/schema/task/spring-task-3.1.xsd

    http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.1.xsd

    http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.1.xsd">

	<context:annotation-config />

	<context:component-scan base-package="com"></context:component-scan>

	<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">

		<property name="locations">

			<list>

				<value>classpath:com/resource/config.properties</value>

			</list>

		</property>

	</bean>

	<bean id="dataSourceOne" class="com.mchange.v2.c3p0.ComboPooledDataSource"

		destroy-method="close">

		<property name="driverClass" value="${dbOne.jdbc.driverClass}" />

		<property name="jdbcUrl" value="${dbOne.jdbc.url}" />

		<property name="user" value="${dbOne.jdbc.user}" />

		<property name="password" value="${dbOne.jdbc.password}" />

		<property name="initialPoolSize" value="${dbOne.jdbc.initialPoolSize}" />

		<property name="minPoolSize" value="${dbOne.jdbc.minPoolSize}" />

		<property name="maxPoolSize" value="${dbOne.jdbc.maxPoolSize}" />

	</bean>

	<bean id="dataSourceTwo" class="com.mchange.v2.c3p0.ComboPooledDataSource"

		destroy-method="close">

		<property name="driverClass" value="${dbTwo.jdbc.driverClass}" />

		<property name="jdbcUrl" value="${dbTwo.jdbc.url}" />

		<property name="user" value="${dbTwo.jdbc.user}" />

		<property name="password" value="${dbTwo.jdbc.password}" />

		<property name="initialPoolSize" value="${dbTwo.jdbc.initialPoolSize}" />

		<property name="minPoolSize" value="${dbTwo.jdbc.minPoolSize}" />

		<property name="maxPoolSize" value="${dbTwo.jdbc.maxPoolSize}" />

	</bean>

	<bean id="dynamicDataSource" class="com.core.DynamicDataSource">

		<property name="targetDataSources">

			<map key-type="java.lang.String">

				<entry value-ref="dataSourceOne" key="dataSourceOne"></entry>

				<entry value-ref="dataSourceTwo" key="dataSourceTwo"></entry>

			</map>

		</property>

		<property name="defaultTargetDataSource" ref="dataSourceOne">

		</property>

	</bean>

	<bean id="sessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">

		<property name="dataSource" ref="dynamicDataSource" />

		<property name="hibernateProperties">

			<props>

				<prop key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop>

				<prop key="hibernate.current_session_context_class">org.springframework.orm.hibernate4.SpringSessionContext</prop>

				<prop key="hibernate.show_sql">false</prop>

				<prop key="hibernate.format_sql">true</prop>

				<prop key="hbm2ddl.auto">create</prop>

			</props>

		</property>

		<property name="packagesToScan">

			<list>

				<value>com.po</value>

			</list>

		</property>

	</bean>

	<bean id="transactionManager" class="org.springframework.orm.hibernate4.HibernateTransactionManager">

		<property name="sessionFactory" ref="sessionFactory" />

	</bean>

	<aop:config>

		<aop:pointcut id="transactionPointCut" expression="execution(* com.dao..*.*(..))" />

		<aop:advisor advice-ref="txAdvice" pointcut-ref="transactionPointCut" />

	</aop:config>

	<tx:advice id="txAdvice" transaction-manager="transactionManager">

		<tx:attributes>

			<tx:method name="add*" propagation="REQUIRED" />

			<tx:method name="save*" propagation="REQUIRED" />

			<tx:method name="update*" propagation="REQUIRED" />

			<tx:method name="delete*" propagation="REQUIRED" />

			<tx:method name="*" read-only="true" />

		</tx:attributes>

	</tx:advice>

	<aop:config>

		<aop:aspect id="dataSourceAspect" ref="dataSourceInterceptor">

			<aop:pointcut id="daoOne" expression="execution(* com.dao.one.*.*(..))" />

			<aop:pointcut id="daoTwo" expression="execution(* com.dao.two.*.*(..))" />

			<aop:before pointcut-ref="daoOne" method="setdataSourceOne" />

			<aop:before pointcut-ref="daoTwo" method="setdataSourceTwo" />

		</aop:aspect>

	</aop:config>

</beans>

2. DynamicDataSource.class

package com.core;

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

public class DynamicDataSource extends AbstractRoutingDataSource{

	@Override

	protected Object determineCurrentLookupKey() {

		return DatabaseContextHolder.getCustomerType();

	}

}

3. DatabaseContextHolder.class　

package com.core;

public class DatabaseContextHolder {

	private static final ThreadLocal<String> contextHolder = new ThreadLocal<String>();

	public static void setCustomerType(String customerType) {

		contextHolder.set(customerType);

	}

	public static String getCustomerType() {

		return contextHolder.get();

	}

	public static void clearCustomerType() {

		contextHolder.remove();

	}

}

　4. DataSourceInterceptor.class

package com.core;

import org.aspectj.lang.JoinPoint;

import org.springframework.stereotype.Component;

@Component

public class DataSourceInterceptor {

	public void setdataSourceOne(JoinPoint jp) {

		DatabaseContextHolder.setCustomerType("dataSourceOne");

	}

	public void setdataSourceTwo(JoinPoint jp) {

		DatabaseContextHolder.setCustomerType("dataSourceTwo");

	}

}

　5. po实体类

package com.po;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.Table;

@Entity

@Table(name = "BTSF_BRAND", schema = "hotel")

public class Brand {

	private String id;

	private String names;

	private String url;

	@Id

	@Column(name = "ID", unique = true, nullable = false, length = 10)

	public String getId() {

		return this.id;

	}

	public void setId(String id) {

		this.id = id;

	}

	@Column(name = "NAMES", nullable = false, length = 50)

	public String getNames() {

		return this.names;

	}

	public void setNames(String names) {

		this.names = names;

	}

	@Column(name = "URL", length = 200)

	public String getUrl() {

		return this.url;

	}

	public void setUrl(String url) {

		this.url = url;

	}

}

　　

package com.po;

import javax.persistence.Column;

import javax.persistence.Entity;

import javax.persistence.Id;

import javax.persistence.Table;

@Entity

@Table(name = "CITY", schema = "car")

public class City {

	private Integer id;

	private String name;

	@Id

	@Column(name = "ID", unique = true, nullable = false)

	public Integer getId() {

		return id;

	}

	public void setId(Integer id) {

		this.id = id;

	}

	@Column(name = "NAMES", nullable = false, length = 50)

	public String getName() {

		return name;

	}

	public void setName(String name) {

		this.name = name;

	}

}

　　6. BrandDaoImpl.class

package com.dao.one;

import java.util.List;

import javax.annotation.Resource;

import org.hibernate.Query;

import org.hibernate.SessionFactory;

import org.springframework.stereotype.Repository;

import com.po.Brand;

@Repository

public class BrandDaoImpl implements IBrandDao {

	@Resource

	protected SessionFactory sessionFactory;

	@SuppressWarnings("unchecked")

	@Override

	public List<Brand> findAll() {

		String hql = "from Brand";

		Query query = sessionFactory.getCurrentSession().createQuery(hql);

		return query.list();

	}

}

　7. CityDaoImpl.class

package com.dao.two;

import java.util.List;

import javax.annotation.Resource;

import org.hibernate.Query;

import org.hibernate.SessionFactory;

import org.springframework.stereotype.Repository;

import com.po.City;

@Repository

public class CityDaoImpl implements ICityDao {

	@Resource

	private SessionFactory sessionFactory;

	@SuppressWarnings("unchecked")

	@Override

	public List<City> find() {

		String hql = "from City";

		Query query = sessionFactory.getCurrentSession().createQuery(hql);

		return query.list();

	}

}

　　8. DaoTest.class

package com.test;

import java.util.List;

import javax.annotation.Resource;

import org.junit.Test;

import org.junit.runner.RunWith;

import org.springframework.test.context.ContextConfiguration;

import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

import org.springframework.test.context.transaction.TransactionConfiguration;

import com.dao.one.IBrandDao;

import com.dao.two.ICityDao;

import com.po.Brand;

import com.po.City;

@RunWith(SpringJUnit4ClassRunner.class)

@ContextConfiguration(locations = "classpath:com/resource/applicationContext.xml")

@TransactionConfiguration(transactionManager = "transactionManager", defaultRollback = false)

public class DaoTest {

	@Resource

	private IBrandDao brandDao;

	@Resource

	private ICityDao cityDao;

	@Test

	public void testList() {

		List<Brand> brands = brandDao.findAll();

		System.out.println(brands.size());

		List<City> cities = cityDao.find();

		System.out.println(cities.size());

	}

}

　　利用aop，达到动态更改数据源的目的。当需要增加数据源的时候，我们只需要在applicationContext配置文件中添加aop配置，新建个DataSourceInterceptor即可。而不需要更改任何代码。

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