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项目背景：项目开发中数据库使用了读写分离，所有查询语句走从库，除此之外走主库。
最简单的办法其实就是建两个包，把之前数据源那一套配置copy一份，指向另外的包，但是这样扩展很有限，所有采用下面的办法。
参考了两篇文章如下：
http://www.weikejianghu.com/article/111840.htm
http://www.weikejianghu.com/article/111842.htm
这两篇文章都对原理进行了分析，下面只写自己的实现过程其他不再叙述。
实现思路是：
第一步，实现动态切换数据源：配置两个DataSource，配置两个SqlSessionFactory指向两个不同的DataSource，两个SqlSessionFactory都用一个SqlSessionTemplate，同时重写Mybatis提供的SqlSessionTemplate类，最后配置Mybatis自动扫描。
第二步，利用aop切面，拦截dao层所有方法，因为dao层方法命名的特点，比如所有查询sql都是select开头，或者get开头等等，拦截这些方法，并把当前数据源切换至从库。
spring中配置如下：
主库数据源配置：
<bean id="masterDataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close">2 <property name="driverClass" value="${master_mysql_jdbc_driver}" />
<property name="jdbcUrl" value="${master_mysql_jdbc_url}" />
<property name="user" value="${master_mysql_jdbc_user}" />
<property name="password" value="${master_mysql_jdbc_password}" />
</bean>
</div>
从库数据源配置：
<bean id="masterDataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close">
<property name="driverClass" value="${slave_mysql_jdbc_driver}" />
<property name="jdbcUrl" value="${slave_mysql_jdbc_url}" />
<property name="user" value="${slave_mysql_jdbc_user}" />
<property name="password" value="${slave_mysql_jdbc_password}" />
</bean>
</div>
主库SqlSessionFactory配置：
<bean id="masterSqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"> <property name="dataSource" ref="masterDataSource" /> <property name="mapperLocations" value="classpath:com/sincetimes/slg/dao/*.xml"/> </bean></div>
从库SqlSessionFactory配置：
<bean id="slaveSqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"> <property name="dataSource" ref="slaveDataSource" /> <property name="mapperLocations" value="classpath:com/sincetimes/slg/dao/*.xml"/> </bean></div>
两个SqlSessionFactory使用同一个SqlSessionTemplate配置：
<bean id="MasterAndSlaveSqlSessionTemplate" class="com.sincetimes.slg.framework.core.DynamicSqlSessionTemplate"> <constructor-arg index="0" ref="masterSqlSessionFactory" /> <property name="targetSqlSessionFactorys"> <map> <entry value-ref="masterSqlSessionFactory" key="master"/> <entry value-ref="slaveSqlSessionFactory" key="slave"/> </map> </property> </bean></div>
配置Mybatis自动扫描dao
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer"> <property name="basePackage" value="com.sincetimes.slg.dao" /> <property name="sqlSessionTemplateBeanName" value="MasterAndSlaveSqlSessionTemplate" /> </bean></div>
自己重写了SqlSessionTemplate代码如下：
package com.sincetimes.slg.framework.core;
import static java.lang.reflect.Proxy.newProxyInstance;
import static org.apache.ibatis.reflection.ExceptionUtil.unwrapThrowable;
import static org.mybatis.spring.SqlSessionUtils.closeSqlSession;
import static org.mybatis.spring.SqlSessionUtils.getSqlSession;
import static org.mybatis.spring.SqlSessionUtils.isSqlSessionTransactional;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.util.List;
import java.util.Map;
import org.apache.ibatis.exceptions.PersistenceException;
import org.apache.ibatis.executor.BatchResult;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.ExecutorType;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.mybatis.spring.MyBatisExceptionTranslator;
import org.mybatis.spring.SqlSessionTemplate;
import org.springframework.dao.support.PersistenceExceptionTranslator;
import org.springframework.util.Assert;
import com.sincetimes.slg.framework.util.SqlSessionContentHolder;
/**
*
* TODO 重写SqlSessionTemplate
* @author ccg
* @version 1.0
* Created 2017年4月21日 下午3:15:15
*/
public class DynamicSqlSessionTemplate extends SqlSessionTemplate {
private final SqlSessionFactory sqlSessionFactory;
private final ExecutorType executorType;
private final SqlSession sqlSessionProxy;
private final PersistenceExceptionTranslator exceptionTranslator;
private Map<Object, SqlSessionFactory> targetSqlSessionFactorys;
private SqlSessionFactory defaultTargetSqlSessionFactory;
public void setTargetSqlSessionFactorys(Map<Object, SqlSessionFactory> targetSqlSessionFactorys) {
this.targetSqlSessionFactorys = targetSqlSessionFactorys;
}
public Map<Object, SqlSessionFactory> getTargetSqlSessionFactorys(){
return targetSqlSessionFactorys;
}
public void setDefaultTargetSqlSessionFactory(SqlSessionFactory defaultTargetSqlSessionFactory) {
this.defaultTargetSqlSessionFactory = defaultTargetSqlSessionFactory;
}
public DynamicSqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
this(sqlSessionFactory, sqlSessionFactory.getConfiguration().getDefaultExecutorType());
}
public DynamicSqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType) {
this(sqlSessionFactory, executorType, new MyBatisExceptionTranslator(sqlSessionFactory.getConfiguration()
.getEnvironment().getDataSource(), true));
}
public DynamicSqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
PersistenceExceptionTranslator exceptionTranslator) {
super(sqlSessionFactory, executorType, exceptionTranslator);
this.sqlSessionFactory = sqlSessionFactory;
this.executorType = executorType;
this.exceptionTranslator = exceptionTranslator;
this.sqlSessionProxy = (SqlSession) newProxyInstance(
SqlSessionFactory.class.getClassLoader(),
new Class[] { SqlSession.class },
new SqlSessionInterceptor());
this.defaultTargetSqlSessionFactory = sqlSessionFactory;
}
@Override
public SqlSessionFactory getSqlSessionFactory() {
SqlSessionFactory targetSqlSessionFactory = targetSqlSessionFactorys.get(SqlSessionContentHolder.getContextType());
if (targetSqlSessionFactory != null) {
return targetSqlSessionFactory;
} else if (defaultTargetSqlSessionFactory != null) {
return defaultTargetSqlSessionFactory;
} else {
Assert.notNull(targetSqlSessionFactorys, "Property 'targetSqlSessionFactorys' or 'defaultTargetSqlSessionFactory' are required");
Assert.notNull(defaultTargetSqlSessionFactory, "Property 'defaultTargetSqlSessionFactory' or 'targetSqlSessionFactorys' are required");
}
return this.sqlSessionFactory;
}
@Override
public Configuration getConfiguration() {
return this.getSqlSessionFactory().getConfiguration();
}
public ExecutorType getExecutorType() {
retur