Spring整合Mybatis实现动态数据源切换教程配置

你的名字 2022-07-20 18:26 209阅读 0赞

原文：[Spring整合Mybatis实现动态数据源切换教程配置][Spring_Mybatis]

[http://www.zuidaima.com/share/1816310397144064.htm][Spring_Mybatis]

**一.摘要**

这篇文章将介绍Spring整合Mybatis 如何完成SqlSessionFactory的动态切换的。并且会简单的介绍下MyBatis整合Spring中的官方的相关代码。

Spring整合MyBatis切换SqlSessionFactory有两种方法，第一、 继承SqlSessionDaoSupport，重写获取SqlSessionFactory的方法。第二、继承SqlSessionTemplate 重写getSqlSessionFactory、getConfiguration和SqlSessionInterceptor这个拦截器。其中最为关键还是继承SqlSessionTemplate 并重写里面的方法。

而Spring整合MyBatis也有两种方式，一种是配置MapperFactoryBean，另一种则是利用MapperScannerConfigurer进行扫描接口或包完成对象的自动创建。相对来说后者更方便些。MapperFactoryBean继承了SqlSessionDaoSupport也就是动态切换SqlSessionFactory的第一种方法，我们需要重写和实现SqlSessionDaoSupport方法，或者是继承MapperFactoryBean来重写覆盖相关方法。如果利用MapperScannerConfigurer的配置整合来切换SqlSessionFactory，那么我们就需要继承SqlSessionTemplate，重写上面提到的方法。在整合的配置中很多地方都是可以注入SqlSessionTemplate代替SqlSessionFactory的注入的。因为SqlSessionTemplate的创建也是需要注入SqlSessionFactory的。

**二.实现代码**

1.继承SqlSessionTemplate 重写getSqlSessionFactory，getConfiguration和SqlSessionInterceptor

package com.hoo.framework.mybatis.support;
     
    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;
     
    /**
     * <b>function:</b> 继承SqlSessionTemplate 重写相关方法
     * @author hoojo
     * @createDate 2013-10-18 下午03:07:46
     * @file CustomSqlSessionTemplate.java
     * @package com.hoo.framework.mybatis.support
     * @project SHMB
     * @blog http://blog.csdn.net/IBM_hoojo
     * @email hoojo_@126.com
     * @version 1.0
     */
    public class CustomSqlSessionTemplate 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 void setDefaultTargetSqlSessionFactory(SqlSessionFactory defaultTargetSqlSessionFactory) {
            this.defaultTargetSqlSessionFactory = defaultTargetSqlSessionFactory;
        }
     
        public CustomSqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
            this(sqlSessionFactory, sqlSessionFactory.getConfiguration().getDefaultExecutorType());
        }
     
        public CustomSqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType) {
            this(sqlSessionFactory, executorType, new MyBatisExceptionTranslator(sqlSessionFactory.getConfiguration()
                    .getEnvironment().getDataSource(), true));
        }
     
        public CustomSqlSessionTemplate(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(CustomerContextHolder.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(
                        CustomSqlSessionTemplate.this.getSqlSessionFactory(),
                        CustomSqlSessionTemplate.this.executorType, 
                        CustomSqlSessionTemplate.this.exceptionTranslator);
                try {
                    Object result = method.invoke(sqlSession, args);
                    if (!isSqlSessionTransactional(sqlSession, CustomSqlSessionTemplate.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 (CustomSqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
                        Throwable translated = CustomSqlSessionTemplate.this.exceptionTranslator
                            .translateExceptionIfPossible((PersistenceException) unwrapped);
                        if (translated != null) {
                            unwrapped = translated;
                        }
                    }
                    throw unwrapped;
                } finally {
                    closeSqlSession(sqlSession, CustomSqlSessionTemplate.this.getSqlSessionFactory());
                }
            }
        }
     
    }

重写后的getSqlSessionFactory方法会从我们配置的SqlSessionFactory集合targetSqlSessionFactorys或默认的defaultTargetSqlSessionFactory中获取Session对象。**而改写的SqlSessionInterceptor 是这个MyBatis整合Spring的关键，所有的SqlSessionFactory对象的session都将在这里完成创建、提交、关闭等操作。所以我们改写这里的代码，在这里获取getSqlSessionFactory的时候，从多个SqlSessionFactory中获取我们设置的那个即可。**

上面添加了targetSqlSessionFactorys、defaultTargetSqlSessionFactory两个属性来配置多个SqlSessionFactory对象和默认的SqlSessionFactory对象。

CustomerContextHolder 设置SqlSessionFactory的类型

package com.hoo.framework.mybatis.support;
    /*
     *多数据源
     */
    
    public abstract class CustomerContextHolder {
     
        public final static String SESSION_FACTORY_MYSQL = "mysql";
        public final static String SESSION_FACTORY_ORACLE = "oracle";
        
        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();  
        }  
    }

2、配置相关的文件applicationContext-session-factory.xml

<?xml version="1.0" encoding="UTF-8"?>
    <beans xmlns="http://www.springframework.org/schema/beans"
        xmlns:aop="http://www.springframework.org/schema/aop" 
        xmlns:tx="http://www.springframework.org/schema/tx"
        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:schemaLocation="http://www.springframework.org/schema/beans 
        http://www.springframework.org/schema/beans/spring-beans-3.2.xsd 
        http://www.springframework.org/schema/aop 
        http://www.springframework.org/schema/aop/spring-aop-3.2.xsd 
        http://www.springframework.org/schema/tx  
        http://www.springframework.org/schema/tx/spring-tx-3.2.xsd ">
        
        
        <bean id="dataSourceOracle" class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close">
            <property name="driverClass" value="${datasource.driver}"/>
            <property name="jdbcUrl" value="${datasource.url}"/>
            <property name="user" value="${datasource.username}"/>
            <property name="password" value="${datasource.password}"/>
                    
            <property name="acquireIncrement" value="${c3p0.acquireIncrement}"/>
            <property name="initialPoolSize" value="${c3p0.initialPoolSize}"/>
            <property name="minPoolSize" value="${c3p0.minPoolSize}"/>
            <property name="maxPoolSize" value="${c3p0.maxPoolSize}"/>
            <property name="maxIdleTime" value="${c3p0.maxIdleTime}"/>
            <property name="idleConnectionTestPeriod" value="${c3p0.idleConnectionTestPeriod}"/>
            <property name="maxStatements" value="${c3p0.maxStatements}"/>
            <property name="numHelperThreads" value="${c3p0.numHelperThreads}"/>
            <property name="preferredTestQuery" value="${c3p0.preferredTestQuery}"/>
            <property name="testConnectionOnCheckout" value="${c3p0.testConnectionOnCheckout}"/>
        </bean>
        
        <bean id="dataSourceMySQL" class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close">
            <property name="driverClass" value="com.mysql.jdbc.Driver"/>
            <property name="jdbcUrl" value="jdbc:mysql://172.31.108.178:3306/world?useUnicode=true&characterEncoding=UTF-8&zeroDateTimeBehavior=convertToNull"/>
            <property name="user" value="root"/>
            <property name="password" value="jp2011"/>
                    
            <property name="acquireIncrement" value="${c3p0.acquireIncrement}"/>
            <property name="initialPoolSize" value="${c3p0.initialPoolSize}"/>
            <property name="minPoolSize" value="${c3p0.minPoolSize}"/>
            <property name="maxPoolSize" value="${c3p0.maxPoolSize}"/>
            <property name="maxIdleTime" value="${c3p0.maxIdleTime}"/>
            <property name="idleConnectionTestPeriod" value="${c3p0.idleConnectionTestPeriod}"/>
            <property name="maxStatements" value="${c3p0.maxStatements}"/>
            <property name="numHelperThreads" value="${c3p0.numHelperThreads}"/>
            <property name="preferredTestQuery" value="${c3p0.preferredTestQuery}"/>
            <property name="testConnectionOnCheckout" value="${c3p0.testConnectionOnCheckout}"/>
        </bean>
        
        
        <bean id="oracleSqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
            <property name="dataSource" ref="dataSourceOracle"/>
            <property name="configLocation" value="classpath:mybatis.xml"/>
             
            <property name="mapperLocations">
                <list>
                     
                    <value>classpath:com/hoo/framework/mybatis/mybatis-common.xml</value>
                    <value>classpath:com/hoo/**/resultmap/*-resultmap.xml</value>
                    <value>classpath:com/hoo/**/mapper/*-mapper.xml</value>
                    <value>classpath:com/hoo/**/mapper/**/*-mapper.xml</value>
                </list>
            </property>
        </bean>
        
        
        <bean id="mysqlSqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
            <property name="dataSource" ref="dataSourceMySQL"/>
            <property name="configLocation" value="classpath:mybatis.xml"/>
              
            <property name="mapperLocations">
                <list>
                     
                    <value>classpath:com/hoo/framework/mybatis/mybatis-common.xml</value>
                    <value>classpath:com/hoo/**/resultmap/*-mysql-resultmap.xml</value>
                    <value>classpath:com/hoo/**/mapper/*-mysql-mapper.xml</value>
                    <value>classpath:com/hoo/**/mapper/**/*-mysql-mapper.xml</value>
                    <value>classpath:com/hoo/**/mapper/**/multiple-datasource-mapper.xml</value>
                </list>
            </property>
        </bean>    
        
        
        <bean id="sqlSessionTemplate" class="com.hoo.framework.mybatis.support.CustomSqlSessionTemplate">
            <constructor-arg ref="oracleSqlSessionFactory" />
            <property name="targetSqlSessionFactorys">
                <map>     
                    <entry value-ref="oracleSqlSessionFactory" key="oracle"/>
                    <entry value-ref="mysqlSqlSessionFactory" key="mysql"/>
                </map> 
            </property>
        </bean>
        
        
        <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
            <property name="basePackage" value="com.hoo.**.mapper"/>
            
            <property name="sqlSessionTemplateBeanName" value="sqlSessionTemplate"/>
            <property name="markerInterface" value="com.hoo.framework.mybatis.SqlMapper"/>
        </bean> 
        
    </beans>

上面的配置关键是在MapperScannerConfigurer中注入sqlSessionTemplate，这个要注意。当我们配置了多个SqlSessionFactoryBean的时候，就需要为MapperScannerConfigurer指定一个sqlSessionFactoryBeanName或是sqlSessionTemplateBeanName。一般情况下注入了sqlSessionTemplateBeanName对象，那sqlSessionFactory也就有值了。如果单独的注入了sqlSessionFactory那么程序会创建一个sqlSessionTemplate对象。我们可以看看代码SqlSessionFactoryDaoSupport对象的代码。如果你不喜欢使用扫描的方式，也可以注入sqlSessionTemplate或继承sqlSessionTemplate完成数据库操作。

public abstract class SqlSessionDaoSupport extends DaoSupport {
     
      private SqlSession sqlSession;
     
      private boolean externalSqlSession;
     
      public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
        if (!this.externalSqlSession) {
          this.sqlSession = new SqlSessionTemplate(sqlSessionFactory);
        }
      }
     
      public void setSqlSessionTemplate(SqlSessionTemplate sqlSessionTemplate) {
        this.sqlSession = sqlSessionTemplate;
        this.externalSqlSession = true;
      }
    ......

这段代码很明显，如果注入了sqlSessionTemplate上面的注入也就不会执行了，如果没有注入sqlSessionTemplate，那么会自动new一个sqlSessionTemplate对象。

3、编写相关测试接口和实现的mapper.xml

package com.hoo.server.datasource.mapper;
     
    import java.util.List;
    import java.util.Map;
    import com.hoo.framework.mybatis.SqlMapper;
    /*
     *MyBatis 多数据源 测试查询接口
     */
    public interface MultipleDataSourceMapper extends SqlMapper {
     
        public List<Map<String, Object>> execute4MySQL() throws Exception;
        
        public List<Map<String, Object>> execute4Oracle() throws Exception;
    }

multiple-datasource-mapper.xml
    
    
    <?xml version="1.0" encoding="UTF-8" ?>
    <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    <mapper namespace="com.hoo.server.datasource.mapper.MultipleDataSourceMapper">
        
        <select id="execute4Oracle" resultType="map">
            <![CDATA[
                SELECT
                    *
                FROM
                    deviceInfo_tab t where rownum < 10
            ]]>
        </select>
        
        <select id="execute4MySQL" resultType="map">
            <![CDATA[
                SELECT
                    *
                FROM
                    city limit 2
            ]]>
        </select>
    </mapper>

上面分别查询oracle和mysql两个数据库中的table

4、测试代码

@Autowired
    @Qualifier("multipleDataSourceMapper")
    private MultipleDataSourceMapper mapper;
     
    @Test
    public void testMapper() {
        CustomerContextHolder.setContextType(CustomerContextHolder.SESSION_FACTORY_MYSQL);
        try {
            trace(mapper.execute4MySQL());
        } catch (Exception e1) {
            e1.printStackTrace();
        }
        CustomerContextHolder.setContextType(CustomerContextHolder.SESSION_FACTORY_ORACLE);
        try {
            trace(mapper.execute4Oracle());
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

运行后发现能够顺利查询出数据。

如果你是重写SqlSessionDaoSupport，那么方法如下

package com.hoo.framework.mybatis.support;
     
    import java.util.Map;
    import org.apache.ibatis.session.SqlSession;
    import org.apache.ibatis.session.SqlSessionFactory;
    import org.mybatis.spring.SqlSessionUtils;
    import org.mybatis.spring.support.SqlSessionDaoSupport;
    import org.springframework.beans.BeansException;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.ApplicationContextAware;
    /*
     *MyBatis 动态SqlSessionFactory
     */
    public class DynamicSqlSessionDaoSupport extends SqlSessionDaoSupport implements ApplicationContextAware {
     
        private ApplicationContext applicationContext;
        
        private Map<Object, SqlSessionFactory> targetSqlSessionFactorys;
        private SqlSessionFactory defaultTargetSqlSessionFactory;
        private SqlSession sqlSession;
     
        @Override
        public final SqlSession getSqlSession() {
            SqlSessionFactory targetSqlSessionFactory = targetSqlSessionFactorys.get(CustomerContextHolder.getContextType());
            if (targetSqlSessionFactory != null) {
                setSqlSessionFactory(targetSqlSessionFactory);
            } else if (defaultTargetSqlSessionFactory != null) {
                setSqlSessionFactory(defaultTargetSqlSessionFactory);
                targetSqlSessionFactory = defaultTargetSqlSessionFactory;
            } else {
                targetSqlSessionFactory = (SqlSessionFactory) applicationContext.getBean(CustomerContextHolder.getContextType());
                setSqlSessionFactory(targetSqlSessionFactory);
            }
            this.sqlSession = SqlSessionUtils.getSqlSession(targetSqlSessionFactory);
            return this.sqlSession;
        }
     
        @Override
        protected void checkDaoConfig() {
            //Assert.notNull(getSqlSession(), "Property 'sqlSessionFactory' or 'sqlSessionTemplate' are required");
        }
     
        public void setTargetSqlSessionFactorys(Map<Object, SqlSessionFactory> targetSqlSessionFactorys) {
            this.targetSqlSessionFactorys = targetSqlSessionFactorys;
        }
     
        public void setDefaultTargetSqlSessionFactory(SqlSessionFactory defaultTargetSqlSessionFactory) {
            this.defaultTargetSqlSessionFactory = defaultTargetSqlSessionFactory;
        }
     
        @Override
        public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
            this.applicationContext = applicationContext;
        }
    }

主要重写getSqlSession方法，上面获取SqlSessionFactory的方法。

重写好了后就可以配置这个对象，配置代码如下

//每一个DAO由继承SqlSessionDaoSupport全部改为DynamicSqlSessionDaoSupport

public class UserMapperDaoImpl extends DynamicSqlSessionDaoSupport implements UserDao {  
      
        public int addUser(User user) {            
            return this.getSqlSession().insert("com.hoo.user.dao.UserDao.addUser", user);  
        }    
    }

在上面的配置文件中加入配置

就这样也可以利用DynamicSqlSessionDaoSupport来完成动态切换sqlSessionFactory对象，只需用在注入userMapperDao调用方法的时候设置下CustomerContextHolder的contextType即可。

**三.总结**

为了实现这个功能看了mybatis-spring-1.2.0.jar这个包的部分源代码，代码内容不是很多。所以看了下主要的代码，下面做些简单的介绍。

MapperScannerConfigurer这个类就是我们要扫描的Mapper接口的类，也就是basePackage中继承markerInterface配置的接口。可以看看ClassPathBeanDefinitionScanner、ClassPathMapperScanner中的doScan这个方法。它会扫描basePackage这个包下所有接口，在ClassPathScanningCandidateComponentProvider中有这个方法findCandidateComponents，它会找到所有的BeanDefinition。

最重要的一点是ClassPathMapperScanner中的doScan这个方法它会给这些接口创建一个MapperFactoryBean。并且会检查sqlSessionFactory和sqlSessionTemplate对象的注入情况。

![20140510114402138.png][]

所以我们配置扫描的方式也就相当于我们在配置文件中给每一个Mapper配置一个MapperFactoryBean一样。而这个MapperFactoryBean又继承SqlSessionDaoSupport。所以当初我想重写MapperScannerConfigurer中的postProcessBeanDefinitionRegistry方法，然后重写方法中的ClassPathMapperScanner中的doScan方法，将definition.setBeanClass(MapperFactoryBean.class);改成自己定义的MapperFactoryBean。最后以失败告终，因为这里是Spring装载扫描对象的时候都已经为这些对象创建好了代理、设置好了mapperInterface和注入需要的类。所以在调用相关操作数据库的API方法的时候，设置对应的SqlSessionFactory也是无效的。

辗转反侧我看到了SqlSessionTemplate这个类，它的功能相当于SqlSessionDaoSupport的实现类MapperFactoryBean。最为关键的是SqlSessionTemplate有一个拦截器SqlSessionInterceptor，它复制所有SqlSession的创建、提交、关闭，而且是在每个方法之前。这点在上面也提到过了！所以我们只需要在SqlSessionInterceptor方法中获取SqlSessionFactory的时候，在这之前调用下CustomerContextHolder.setContextType方法即可完成数据库的SqlSessionFactory的切换。而在MapperScannerConfigurer提供了注入SqlSessionFactory和sqlSessionTemplate的方法，如果注入了SqlSessionFactory系统将会new一个sqlSessionTemplate，而注入了sqlSessionTemplate就不会创建其他对象（见下面代码）。所以我们配置一个sqlSessionTemplate并注入到MapperScannerConfigurer中，程序将会使用这个sqlSessionTemplate。本文最后的实现方式就是这样完成的。

public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
      if (!this.externalSqlSession) {
        this.sqlSession = new SqlSessionTemplate(sqlSessionFactory);
      }
    }
     
    public void setSqlSessionTemplate(SqlSessionTemplate sqlSessionTemplate) {
      this.sqlSession = sqlSessionTemplate;
      this.externalSqlSession = true;
    }

原文地址：[http://www.blogjava.net/hoojo/archive/2013/10/22/405488.html][http_www.blogjava.net_hoojo_archive_2013_10_22_405488.html]

欢迎拜访！

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[http_www.blogjava.net_hoojo_archive_2013_10_22_405488.html]: http://www.blogjava.net/hoojo/archive/2013/10/22/405488.html