spring+mybatis多数据源动态切换

 spring mvc+mybatis+多数据源切换 选取oracle,mysql作为例子切换数据源。oracle为默认数据源，在测试的action中，进行mysql和oracle的动态切换。

web.xml

<context-param>  
        <param-name>webAppRootKey</param-name>  
        <param-value>trac</param-value>  
    </context-param>  
  
    <!-- Spring的log4j监听器 -->  
    <listener>  
        <listener-class>org.springframework.web.util.Log4jConfigListener</listener-class>  
    </listener>  
  
    <!-- 字符集 过滤器 -->  
    <filter>  
        <filter-name>CharacterEncodingFilter</filter-name>  
        <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>  
        <init-param>  
            <param-name>encoding</param-name>  
            <param-value>utf8</param-value>  
        </init-param>  
        <init-param>  
            <param-name>forceEncoding</param-name>  
            <param-value>true</param-value>  
        </init-param>  
    </filter>  
    <filter-mapping>  
        <filter-name>CharacterEncodingFilter</filter-name>  
        <url-pattern>/*</url-pattern>  
    </filter-mapping>  
  
    <!-- Spring view分发器 -->  
    <servlet>  
        <servlet-name>dispatcher</servlet-name>  
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>  
        <init-param>  
            <param-name>contextConfigLocation</param-name>  
            <param-value>/WEB-INF/dispatcher.xml</param-value>  
        </init-param>  
        <load-on-startup>1</load-on-startup>  
    </servlet>  
    <servlet-mapping>  
        <servlet-name>dispatcher</servlet-name>  
        <url-pattern>*.action</url-pattern>  
    </servlet-mapping>  
      
    <listener>  
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>  
    </listener> 

applicationContext.xml 

<bean id="parentDataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">  
    </bean>  
      
    <bean id="mySqlDataSource" parent="parentDataSource">  
        <property name="driverClassName" value="com.mysql.jdbc.Driver"></property>  
        <property name="url" value="jdbc:mysql://localhost:3306/test"></property>  
        <property name="username" value="root"></property>  
        <property name="password" value="root"></property>  
    </bean>  
      
    <bean id="oracleDataSource" parent="parentDataSource">  
        <property name="driverClassName" value="oracle.jdbc.driver.OracleDriver"></property>  
        <property name="url" value="jdbc:oracle:thin:@10.16.17.40:1531:addb"></property>  
        <property name="username" value="trac"></property>  
        <property name="password" value="trac"></property>  
    </bean>  
      
    <bean id="dataSource" class="com.trac.dao.datasource.DataSources">  
        <property name="targetDataSources">  
            <map key-type="java.lang.String">  
                <entry value-ref="mySqlDataSource" key="MYSQL"></entry>  
                <entry value-ref="oracleDataSource" key="ORACLE"></entry>  
            </map>  
        </property>  
        <property name="defaultTargetDataSource" ref="oracleDataSource"></property>  
    </bean>  
  
    <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">  
        <property name="dataSource" ref="dataSource" />  
    </bean>  
  
    <!-- 创建SqlSessionFactory，同时指定数据源和mapper -->  
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">  
        <property name="dataSource" ref="dataSource" />  
        <property name="mapperLocations" value="classpath*:com/trac/ibatis/dbcp/*.xml" />  
    </bean>  
  
    <bean id="sqlSession" class="org.mybatis.spring.SqlSessionTemplate">  
        <constructor-arg index="0" ref="sqlSessionFactory" />  
    </bean>  
  
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">  
        <property name="basePackage" value="com.trac.dao" />  
    </bean> 

配置 parentDataSource 的父bean.再配置多个数据源继承这个父bean,对driverClass,url,username,password,等数据源连接参数进行各自的重写。例如 mySqlDataSource ，在 DataSources bean中注入所有要切换的数据源，并且设置默认的数据源。 

DataSourceInstances.java 

public class DataSourceInstances{  
    public static final String MYSQL="MYSQL";  
    public static final String ORACLE="ORACLE";  
}   

DataSourceSwitch.java 

public class DataSourceSwitch{  
    private static final ThreadLocal contextHolder=new ThreadLocal();  
      
    public static void setDataSourceType(String dataSourceType){  
        contextHolder.set(dataSourceType);  
    }  
      
    public static String getDataSourceType(){  
        return (String) contextHolder.get();  
    }  
      
    public static void clearDataSourceType(){  
        contextHolder.remove();  
    }  
}  

　　

DataSources.java 

import org.springframework.jdbc.datasource.lookup.AbstractRoutingDataSource;  
  
public class DataSources extends AbstractRoutingDataSource{  
  
    @Override  
    protected Object determineCurrentLookupKey() {  
        return DataSourceSwitch.getDataSourceType();  
    }  
  
}  

　　

测试

@Controller  
@SuppressWarnings("unused")  
public class TestAction {  
@Autowired  
    TestMapper testMapper;  
  
   @RequestMapping("/test.action")  
    public ModelAndView test(  
            HttpServletRequest request,  
            HttpServletResponse resp){  
        ModelAndView model = new ModelAndView("test");  
        model.addObject("test1", "这是一个测试,获取默认数据连接MYSQL:"+testMapper.test());  
        DataSourceSwitch.setDataSourceType(DataSourceInstances.ORACLE);  
        model.addObject("test2", "这是一个测试,获取数据连接ORACLE:"+testMapper.test());  
        DataSourceSwitch.setDataSourceType(DataSourceInstances.MYSQL);  
        model.addObject("test3", "这是一个测试,获取数据连接MYSQL:"+testMapper.test());  
        return model;  
    }  
} 

代码解释:

查看AbstractRoutingDataSource中的获取数据库连接源码

    public Connection getConnection()
        throws SQLException
    {
        return determineTargetDataSource().getConnection();
    }

查看determineTargetDataSource方法

protected DataSource determineTargetDataSource()
    {
        Assert.notNull(resolvedDataSources, "DataSource router not initialized");
        Object lookupKey = determineCurrentLookupKey();
        DataSource dataSource = (DataSource)resolvedDataSources.get(lookupKey);
        if(dataSource == null && (lenientFallback || lookupKey == null))
            dataSource = resolvedDefaultDataSource;
        if(dataSource == null)
            throw new IllegalStateException((new StringBuilder()).append("Cannot determine target DataSource for lookup key [").append(lookupKey).append("]").toString());
        else
            return dataSource;
    }

其中DataSource dataSource = (DataSource)resolvedDataSources.get(lookupKey); 中的resolvedDataSources 就是我们spring中设置的targetDataSources,是一个Map类型，里面有我们设置的MYSQL和ORACLE数据库连接池

注意determineCurrentLookupKey方法,

protected abstract Object determineCurrentLookupKey();

是一个抽象方法,需要我们去实现,我们将数据源对应的KEY放在本地线程中,那么可以随时在代码中进行切换数据源

默认数据源

在spring配置文件中，我们将defaultTargetDataSource注入到AbstractRoutingDataSource中

public void afterPropertiesSet()
    {
        if(targetDataSources == null)
            throw new IllegalArgumentException("Property 'targetDataSources' is required");
        resolvedDataSources = new HashMap(targetDataSources.size());
        Object lookupKey;
        DataSource dataSource;
        for(Iterator iterator = targetDataSources.entrySet().iterator(); iterator.hasNext(); resolvedDataSources.put(lookupKey, dataSource))
        {
            java.util.Map.Entry entry = (java.util.Map.Entry)iterator.next();
            lookupKey = resolveSpecifiedLookupKey(entry.getKey());
            dataSource = resolveSpecifiedDataSource(entry.getValue());
        }

        if(defaultTargetDataSource != null)
            resolvedDefaultDataSource = resolveSpecifiedDataSource(defaultTargetDataSource);
    }

AbstractRoutingDataSource类实现了InitializingBean接口,项目启动会实现方法afterPropertiesSet,生成resolvedDefaultDataSource实例,这样在determineTargetDataSource方法中如果获取本地线程变量中的连接位空，那么就选择默认数据源。