Spring + Mybatis 项目实现动态切换数据源

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://blog.csdn.net/zl3450341/article/details/20150687

http://www.blogjava.net/hoojo/archive/2013/10/22/405488.html

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">
     <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>

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>

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>

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>

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>

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>

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() {
         return this.executorType;
     }

     public PersistenceExceptionTranslator getPersistenceExceptionTranslator() {
         return this.exceptionTranslator;
     }

     /**
      * {@inheritDoc}
      */
     public <T> T selectOne(String statement) {
         return this.sqlSessionProxy.<T> selectOne(statement);
     }

     /**
      * {@inheritDoc}
      */
     public <T> T selectOne(String statement, Object parameter) {
         return this.sqlSessionProxy.<T> selectOne(statement, parameter);
     }

     /**
      * {@inheritDoc}
      */
     public <K, V> Map<K, V> selectMap(String statement, String mapKey) {
         return this.sqlSessionProxy.<K, V> selectMap(statement, mapKey);
     }

     /**
      * {@inheritDoc}
      */
     public <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey) {
         return this.sqlSessionProxy.<K, V> selectMap(statement, parameter, mapKey);
     }

     /**
      * {@inheritDoc}
      */
     public <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey, RowBounds rowBounds) {
         return this.sqlSessionProxy.<K, V> selectMap(statement, parameter, mapKey, rowBounds);
     }

     /**
      * {@inheritDoc}
      */
     public <E> List<E> selectList(String statement) {
         return this.sqlSessionProxy.<E> selectList(statement);
     }

     /**
      * {@inheritDoc}
      */
     public <E> List<E> selectList(String statement, Object parameter) {
         return this.sqlSessionProxy.<E> selectList(statement, parameter);
     }

     /**
      * {@inheritDoc}
      */
     public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
         return this.sqlSessionProxy.<E> selectList(statement, parameter, rowBounds);
     }

     /**
      * {@inheritDoc}
      */
     public void select(String statement, ResultHandler handler) {
         this.sqlSessionProxy.select(statement, handler);
     }

     /**
      * {@inheritDoc}
      */
     public void select(String statement, Object parameter, ResultHandler handler) {
         this.sqlSessionProxy.select(statement, parameter, handler);
     }

     /**
      * {@inheritDoc}
      */
     public void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {
         this.sqlSessionProxy.select(statement, parameter, rowBounds, handler);
     }

     /**
      * {@inheritDoc}
      */
     public int insert(String statement) {
         return this.sqlSessionProxy.insert(statement);
     }

     /**
      * {@inheritDoc}
      */
     public int insert(String statement, Object parameter) {
         return this.sqlSessionProxy.insert(statement, parameter);
     }

     /**
      * {@inheritDoc}
      */
     public int update(String statement) {
         return this.sqlSessionProxy.update(statement);
     }

     /**
      * {@inheritDoc}
      */
     public int update(String statement, Object parameter) {
         return this.sqlSessionProxy.update(statement, parameter);
     }

     /**
      * {@inheritDoc}
      */
     public int delete(String statement) {
         return this.sqlSessionProxy.delete(statement);
     }

     /**
      * {@inheritDoc}
      */
     public int delete(String statement, Object parameter) {
         return this.sqlSessionProxy.delete(statement, parameter);
     }

     /**
      * {@inheritDoc}
      */
     public <T> T getMapper(Class<T> type) {
         return getConfiguration().getMapper(type, this);
     }

     /**
      * {@inheritDoc}
      */
     public void commit() {
         throw new UnsupportedOperationException("Manual commit is not allowed over a Spring managed SqlSession");
     }

     /**
      * {@inheritDoc}
      */
     public void commit(boolean force) {
         throw new UnsupportedOperationException("Manual commit is not allowed over a Spring managed SqlSession");
     }

     /**
      * {@inheritDoc}
      */
     public void rollback() {
         throw new UnsupportedOperationException("Manual rollback is not allowed over a Spring managed SqlSession");
     }

     /**
      * {@inheritDoc}
      */
     public void rollback(boolean force) {
         throw new UnsupportedOperationException("Manual rollback is not allowed over a Spring managed SqlSession");
     }

     /**
      * {@inheritDoc}
      */
     public void close() {
         throw new UnsupportedOperationException("Manual close is not allowed over a Spring managed SqlSession");
     }

     /**
      * {@inheritDoc}
      */
     public void clearCache() {
         this.sqlSessionProxy.clearCache();
     }

     /**
      * {@inheritDoc}
      */
     public Connection getConnection() {
         return this.sqlSessionProxy.getConnection();
     }

     /**
      * {@inheritDoc}
      * @since 1.0.2
      */
     public List<BatchResult> flushStatements() {
         return this.sqlSessionProxy.flushStatements();
     }

     /**
      * Proxy needed to route MyBatis method calls to the proper SqlSession got from Spring's Transaction Manager It also
      * unwraps exceptions thrown by {@code Method#invoke(Object, Object...)} to pass a {@code PersistenceException} to
      * the {@code PersistenceExceptionTranslator}.
      */
     private class SqlSessionInterceptor implements InvocationHandler {
         public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
             final SqlSession sqlSession = getSqlSession(
                     DynamicSqlSessionTemplate.this.getSqlSessionFactory(),
                     DynamicSqlSessionTemplate.this.executorType,
                     DynamicSqlSessionTemplate.this.exceptionTranslator);
             try {
                 Object result = method.invoke(sqlSession, args);
                 if (!isSqlSessionTransactional(sqlSession, DynamicSqlSessionTemplate.this.getSqlSessionFactory())) {
                     // force commit even on non-dirty sessions because some databases require
                     // a commit/rollback before calling close()
                     sqlSession.commit(true);
                 }
                 return result;
             } catch (Throwable t) {
                 Throwable unwrapped = unwrapThrowable(t);
                 if (DynamicSqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
                     Throwable translated = DynamicSqlSessionTemplate.this.exceptionTranslator
                         .translateExceptionIfPossible((PersistenceException) unwrapped);
                     if (translated != null) {
                         unwrapped = translated;
                     }
                 }
                 throw unwrapped;
             } finally {
                 closeSqlSession(sqlSession, DynamicSqlSessionTemplate.this.getSqlSessionFactory());
             }
         }
     }

 }

SqlSessionContentHolder类代码如下：

 package com.sincetimes.slg.framework.util;

 public abstract class SqlSessionContentHolder {

     public final static String SESSION_FACTORY_MASTER = "master";
     public final static String SESSION_FACTORY_SLAVE = "slave";

     private static final ThreadLocal<String> contextHolder = new ThreadLocal<String>();  

     public static void setContextType(String contextType) {
         contextHolder.set(contextType);
     }  

     public static String getContextType() {
         return contextHolder.get();
     }  

     public static void clearContextType() {
         contextHolder.remove();
     }
 }

最后就是写切面去对dao所有方法进行处理了，代码很简单如下：

 package com.sincetimes.slg.framework.core;

 import org.aspectj.lang.JoinPoint;
 import org.aspectj.lang.annotation.Aspect;
 import org.aspectj.lang.annotation.Before;
 import org.aspectj.lang.annotation.Pointcut;

 import com.sincetimes.slg.framework.util.SqlSessionContentHolder;

 @Aspect
 public class DynamicDataSourceAspect {

     @Pointcut("execution( * com.sincetimes.slg.dao.*.*(..))")
     public void pointCut(){

     }
     @Before("pointCut()")
     public void before(JoinPoint jp){
         String methodName = jp.getSignature().getName();
         //dao方法查询走从库
         if(methodName.startsWith("query") || methodName.startsWith("get") || methodName.startsWith("count") || methodName.startsWith("list")){
             SqlSessionContentHolder.setContextType(SqlSessionContentHolder.SESSION_FACTORY_SLAVE);
         }else{
             SqlSessionContentHolder.setContextType(SqlSessionContentHolder.SESSION_FACTORY_MASTER);
         }
     }

 }