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

 
 
  
   
  
   
  
   
     
       
        classpath:com/resource/config.properties 
       
     
   
  
   
     
     
     
     
     
     
     
   
  
   
     
     
     
     
     
     
     
   
  
   
     
       
     
     
     
   
  
   
     
     
       
        org.hibernate.dialect.MySQLDialect 
        org.springframework.orm.hibernate4.SpringSessionContext 
        false 
        true 
        create 
       
     
     
       
        com.po 
       
     
   
  
   
     
   
  
   
     
     
   
  
   
     
       
       
       
       
       
     
   
  
   
     
       
       
       
       
     
   

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 contextHolder = new ThreadLocal(); 
  
  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

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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 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 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 brands = brandDao.findAll();
    System.out.println(brands.size());
  
    List 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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