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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;@Componentpublic 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;@Repositorypublic 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;@Repositorypublic 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());	}}
      
     

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。