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Spring AOP 动态多数据源的实例详解
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。
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：
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.xsd
http://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 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 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 动态数据源 -->
<bean 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 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 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 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");
}
}
