我們在開發項目的時候經常會遇到數據源這個問題，特別是在數據同步的時候，下面錯新技術頻道小編就給大家介紹Spring AOP 動態多數據源的實例詳解。
?Spring AOP 動態多數據源的實例詳解
當項目中使用到讀寫分離的時候，我們就會遇到多數據源的問題。多數據源讓人最頭痛的，不是配置多個數據源，而是如何能靈活動態的切換數據源。例如在一個spring和Mybatis的框架的項目中，我們在spring配置中往往是配置一個dataSource來連接數據庫，然后綁定給sessionFactory，在dao層代碼中再指定sessionFactory來進行數據庫操作。
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正如上圖所示，每一塊都是指定綁死的，如果是多個數據源，也只能是下圖中那種方式。
可看出在Dao層代碼中寫死了兩個SessionFactory，這樣日后如果再多一個數據源，還要改代碼添加一個SessionFactory，顯然這并不符合開閉原則。
那么正確的做法應該是：
具體代碼與配置如下:
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&characterEncoding=UTF-8&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&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 動態數據源 --> <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> <!-- 多數據源 aop --> <bean id="DataSourceAspect" class="com.carl.dbUtil.DataSourceAspect" /> <aop:config> <aop:advisor pointcut="execution(* com.carl.o2o.mgr.*.*(..))" advice-ref="DataSourceAspect" /> </aop:config> <!-- 事務 --> <bean name="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager"> <property name="dataSource" ref="dynamicDataSource"></property> </bean> </beans>2、DynamicDataSource
DynamicDataSource使用Spring中的代碼結合AOP實現多數據源切換.
public class DynamicDataSource extends AbstractRoutingDataSource { public DynamicDataSource() { } protected Object determineCurrentLookupKey() { return DBContextHolder.getDbType(); } public Logger getParentLogger() { return null; }}3、DBContextHolder
DynamicDataSource的輔助類，用于實際的切換多數據源。
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
多數據源AOP切面編程實現。
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"); }}通過以上的介紹，相信大家已經知道了Spring AOP 動態多數據源的實例詳解，大家按照上面的方法來操作，就能獲得想要的效果了。
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