深入理解spring多数据源配置

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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