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。

 

多数据源配置时的重点：

1. 注意事务拦截器的配置

这是首要的一条。首先你要明白，Spring的事务管理是与数据源绑定的，一旦程序执行到事务管理的那一层（如service）的话，由于在进入该层之前事务已经通过拦截器开启，因此在该层切换数据源是不行的，明白事务的原理是尤为重要的，我之前的文章中，将切换数据源的拦截器配置在了Dao层是有问题的（因为是示例，所以粗心了，对误导了大家我表示道歉），但提供的思路是没有问题的。

Demo中将切换数据源的拦截器（dataSourceInterceptor）配置在了事务拦截器（txadvice）的上一层，也就是Controller层。

2. 注意数据库表的创建

一些人喜欢用hibernate的自动创建表的功能，但需要注意，在多数据源中，尤其是不同数据库的多数据源，想都自动建表是不行的。因为Hibernate自动建表是在项目启动时触发的，因此只会建立项目配置的默认数据源的表，而其他数据源的表则不会自动创建。大家要注意着点。

3. Hibernate的数据库方言（dialect）可以忽略

在多数据源时，方言的设置可以忽略，Hibernate在使用时会自动识别不同的数据库，因此不必纠结这个配置，甚至不配置也可以。

4. 报No current session错误

这个是因为使用了sessionFactory.getCurrentSession()导致的，current session是与线程绑定的，一个线程只会开启一个Session（除非使用openSession()就不会报错），因此需要设置session与线程的绑定关系。

Demo中使用了Spring管理Hibernate的session，因此在web.xml中配置了OpenSessionInViewFilter，并在hibernate.cfg.xml中配置了current_session_context_class。【PS：使用Spring管理Hibernate时，可以去掉hibernate.cfg.xml，而全部配置的Spring的配置文件里，即hibernateProperties