Spring AOP 动态多数据源

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当项目中使用到读写分离的时候，我们就会遇到多数据源的问题。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Mybatis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。
这里写图片描述
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：
这里写图片描述

具体代码与配置如下:

1、applicationContext-mgr.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:context="http://www.springframework.org/schema/context"     xmlns:tx="http://www.springframework.org/schema/tx"    xmlns:p="http://www.springframework.org/schema/p"    xsi:schemaLocation="http://www.springframework.org/schema/beans         http://www.springframework.org/schema/beans/spring-beans-2.5.xsdhttp://www.springframework.org/schema/aop/spring-aop-2.5.xsd       http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-2.5.xsd       http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-2.5.xsd">    <!-- use annotation -->    <context:annotation-config />        <context:component-scan base-package="com.carl.o2o.**.mgr">    </context:component-scan>    <!-- master -->    <bean id="master" class="com.mchange.v2.c3p0.ComboPooledDataSource">        <property name="driverClass" value="${driverClassName_master}"/>        <property name="user" value="${username_master}"/>        <property name="password" value="${password_master}"/>        <property name="jdbcUrl" value="${url_master}?Unicode=true&amp;characterEncoding=UTF-8&amp;allowMultiQueries=true"/>        <property name="maxPoolSize" value="150"/>          <property name="minPoolSize" value="10"/>          <property name="initialPoolSize" value="20"/>          <property name="maxIdleTime" value="3600"/>          <property name="acquireIncrement" value="10"/>          <property name="idleConnectionTestPeriod" value="1800"/>        </bean>    <!-- slave -->    <bean id="slave" class="com.mchange.v2.c3p0.ComboPooledDataSource">        <property name="driverClass" value="${driverClassName_slave}"/>        <property name="user" value="${username_slave}"/>        <property name="password" value="${password_slave}"/>        <property name="jdbcUrl" value="${url_slave}?Unicode=true&amp;characterEncoding=UTF-8"/>        <property name="maxPoolSize" value="150"/>          <property name="minPoolSize" value="10"/>          <property name="initialPoolSize" value="20"/>          <property name="maxIdleTime" value="3600"/>          <property name="acquireIncrement" value="10"/>          <property name="idleConnectionTestPeriod" value="1800"/>        </bean>    <!-- spring 动态数据源 -->    <bean id="dynamicDataSource" class="com.carl.dbUtil.DynamicDataSource">        <property name="targetDataSources">             <map key-type="java.lang.String">                  <entry key="slave" value-ref="slave" />              </map>         </property>         <property name="defaultTargetDataSource" ref="master" />         </bean>      <!-- mybatis mapper config -->    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">        <property name="dataSource" ref="dynamicDataSource"/>        <property name="configLocation" value="classpath:o2o_mybatis_config.xml"/>        <property name="mapperLocations" >            <list>                <value>classpath:sqlMap/*.xml</value>                <value>classpath*:/com/carl/o2o/**/*.xml</value>            </list>        </property>    </bean>    <bean id="sqlSession" class="org.mybatis.spring.SqlSessionTemplate">        <constructor-arg index="0" ref="sqlSessionFactory"></constructor-arg>    </bean>    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">        <property name="basePackage" value="com.carl.o2o.**.mgr.dao" />    </bean>    <!-- 多数据源 aop -->    <bean id="DataSourceAspect" class="com.carl.dbUtil.DataSourceAspect" />    <aop:config>          <aop:advisor pointcut="execution(* com.carl.o2o.mgr.*.*(..))" advice-ref="DataSourceAspect" />    </aop:config>      <!-- 事务 -->    <bean name="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">           <property name="dataSource" ref="dynamicDataSource"></property>    </bean> </beans>

2、DynamicDataSource

DynamicDataSource使用Spring中的代码结合AOP实现多数据源切换.

public class DynamicDataSource extends AbstractRoutingDataSource {    public DynamicDataSource() {    }    protected Object determineCurrentLookupKey() {        return DBContextHolder.getDbType();    }    public Logger getParentLogger() {        return null;    }}

3、DBContextHolder

DynamicDataSource的辅助类，用于实际的切换多数据源。

public class DBContextHolder {    private static ThreadLocal<String> contextHolder = new ThreadLocal();    public static String MASTER = "master";    public static String SLAVE = "slave";    public DBContextHolder() {    }    public static String getDbType() {        String db = (String)contextHolder.get();        if(db == null) {            db = MASTER;        }        return db;    }    public static void setDbType(String str) {        contextHolder.set(str);    }    public static void setMaster() {        contextHolder.set(MASTER);    }    public static void setSlave() {        contextHolder.set(SLAVE);    }    public static void clearDBType() {        contextHolder.remove();    }}

4、DataSourceAspect

多数据源AOP切面编程实现。

public class DataSourceAspect implements MethodBeforeAdvice, AfterReturningAdvice, ThrowsAdvice {    private static final Logger log = LogManager.getLogger(DataSourceAspect.class);    public DataSourceAspect() {    }    public void before(Method m, Object[] args, Object target) throws Throwable {        try {            if(m != null) {                if((m.getName().startsWith("list") || m.getName().startsWith("select") || m.getName().startsWith("get")                 || m.getName().startsWith("count")) && !m.getName().contains("FromMaster")) {                    DBContextHolder.setDbType("slave");                } else {                    DBContextHolder.setDbType("master");                }            }        } catch (Exception var5) {            log.error("data source aspect error.", var5);        }    }    public void after(JoinPoint point) {        log.info("clear db type after method.current id {}", new Object[]{Long.valueOf(Thread.currentThread().getId())});        DBContextHolder.clearDBType();    }    public void afterReturning(Object returnValue, Method method, Object[] args, Object target) throws Throwable {    }    public void afterThrowing(Method method, Object[] args, Object target, Exception ex) throws Throwable {        log.info("current db type {} when exception", new Object[]{DBContextHolder.getDbType()});        DBContextHolder.setDbType("master");    }}

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