Spring AOP 动态多数据源的实例详解

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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="https://www.springframework.org/schema/beans"
  xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance" 
  xmlns:aop="https://www.springframework.org/schema/aop"
  xmlns:context="https://www.springframework.org/schema/context" 
  xmlns:tx="https://www.springframework.org/schema/tx"
  xmlns:p="https://www.springframework.org/schema/p"
  xsi:schemaLocation="https://www.springframework.org/schema/beans 
  https://www.springframework.org/schema/beans/spring-beans-2.5.xsd
https://www.springframework.org/schema/aop/spring-aop-2.5.xsd
  https://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context-2.5.xsd
  https://www.springframework.org/schema/tx https://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 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");
  }
}

以上就是 Spring AOP 动态多数据源的实例详解，如有疑问请留言或者到本站社区交流讨论，感谢阅读，希望能帮助到大家，谢谢大家对本站的支持！