Mybatis+ Spring + JTA

多库数据源深入分析（Mybatis+ Spring + JTA）（一）

博客分类：

• java

多库 多数据源 AbstractRoutingDataSource JTA 

 

最近搭建架构，碰到JTA和事务Transaction的问题，在此做个总结：

 

架构：Mybatis+ Spring

 

技术：spring的AbstractRoutingDataSource和JTA

 

老规矩，先贴代码，在讲原理，刚开始的时候不使用JTA，代码如下：

 

 

/**
* DataSource上下文句柄，通过此类设置需要访问的对应数据源
*
*/
public class DataSourceContextHolder {

    /**
     * DataSource上下文，每个线程对应相应的数据源key
     */
    public static final ThreadLocal contextHolder = new ThreadLocal();

    public static void setDataSourceType(String dataSourceType)
    {
        contextHolder.set(dataSourceType);
    }

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

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

 

 

 

/**
* 动态数据源
*
*/
public class DynamicDataSource extends AbstractRoutingDataSource {

    @Override
    protected Object determineCurrentLookupKey() {
        return DataSourceContextHolder.getDataSourceType();
    }

}

 

 

spring中配置如下：

 

 

<!-- 配置数据源 -->
        <bean id="ds1" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"
                lazy-init="false">
                <property name="driverClassName" value="${jdbc.ds1.driverClassName}" />
                <property name="url" value="${jdbc.ds1.url}" />
                <property name="username" value="${jdbc.ds1.username}" />
                <property name="password" value="${jdbc.ds1.password}" />
                <property name="initialSize" value="5" />
                <property name="maxActive" value="10" />
                <property name="maxWait" value="60000" />
                <property name="poolPreparedStatements" value="true" />
        </bean>

        <bean id="ds2" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"
                lazy-init="false">
                <property name="driverClassName" value="${jdbc.ds2.driverClassName}" />
                <property name="url" value="${jdbc.ds2.url}" />
                <property name="username" value="${jdbc.ds2.username}" />
                <property name="password" value="${jdbc.ds2.password}" />
                <property name="initialSize" value="5" />
                <property name="maxActive" value="10" />
                <property name="maxWait" value="60000" />
                <property name="poolPreparedStatements" value="true" />
        </bean>

        <!-- 动态数据源 -->
        <bean id="dataSource" class="xxx.DynamicDataSource">
                <property name="targetDataSources">
                        <map>
                                <entry key="ds1" value-ref="ds1" />
                                <entry key="ds2" value-ref="ds2" />
                        </map>
                </property>
                <property name="defaultTargetDataSource" ref="ds1" />

        </bean>

        <!-- 事务管理 -->
        <bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
                <property name="dataSource" ref="dataSource" />
        </bean>
        <tx:annotation-driven/>

        <!-- myBatis配置 -->
        <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
                <property name="configLocation" value="classpath:mybatis-config.xml" />
                <property name="dataSource" ref="dataSource" />
        </bean>

<span style="white-space: pre;">        </span><!-- DAO层由 MapperScannerConfigurer自动生成mapper bean -->
        <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
                <property name="basePackage" value="xxx.mapper" />
        </bean>

 

因为每个Service目前只可能访问一个DataSource，所以在调用Service的时候，调用DataSourceContextHolder.setDataSourceType(key)（key可以为ds1,ds2），

就可以动态切换数据源了（当然最好用AOP思想，技术上spring + AspectJ，在每个Service需要的方法切上一刀），

而且对于spring的@Transactional事务管理是起作用的

 

 

OK，按照这种模式，如果Service可能访问多个库，就将DataSourceTransactionManager换成JtaTransactionManager

 

 

<bean id="transactionManager"
        class="org.springframework.transaction.jta.JtaTransactionManager" />
    <tx:annotation-driven transaction-manager="transactionManager" />

 

当然，Datasource换成JNDI获取

 

 

<!-- 创建数据源。 -->
    <bean id="ds1" class="org.springframework.jndi.JndiObjectFactoryBean">
        <property name="jndiName">
            <value>ds1</value>
        </property>
        <property name="resourceRef">
            <value>true</value>
        </property>
    </bean>
    <bean id="ds2" class="org.springframework.jndi.JndiObjectFactoryBean">
        <property name="jndiName">
            <value>ds2</value>
        </property>
        <property name="resourceRef">
            <value>true</value>
        </property>
    </bean>

 

在spring的@Transactional事务管理中，那是死活无法切换数据源

接上篇，为什么此种模式下，在spring托管CMT管理的JTA事务中，无法切换数据源，忙活了好久，对着日志流程和源代码，貌似问题出现在下面的代码中：

 

 

org.mybatis.spring .SqlSessionUtils

public static SqlSession getSqlSession方法：


SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);

//7.当前在事务中，且session的holder存在，则取得当前事务的session
if (holder != null && holder.isSynchronizedWithTransaction()) {

            if (logger.isDebugEnabled()) {
                logger.debug("Fetched SqlSession [" + holder.getSqlSession() + "] from current transaction");
            }

            return holder.getSqlSession();
        }


if (logger.isDebugEnabled()) {
            logger.debug("Creating SqlSession with JDBC Connection [" + conn + "]");
}

//1.创建SqlSession
SqlSession session = sessionFactory.openSession(executorType, conn);

//2.判断当前有事务
if (TransactionSynchronizationManager.isSynchronizationActive()) {
            if (logger.isDebugEnabled()) {
                logger.debug("Registering transaction synchronization for SqlSession [" + session + "]");
            }

//3.创建当前session的holder
            holder = new SqlSessionHolder(session, executorType, exceptionTranslator);

//4.将session的holder注册到事务中
 TransactionSynchronizationManager.bindResource(sessionFactory, holder);
TransactionSynchronizationManager.registerSynchronization(new SqlSessionSynchronization(holder, sessionFactory));
            holder.setSynchronizedWithTransaction(true);
            holder.requested();

//5.（8.）执行sql。。。。

public static void closeSqlSession方法：
SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);

//6.（9.）释放掉当前事务的session
if ((holder != null) && (holder.getSqlSession() == session)) {
     if (logger.isDebugEnabled()) {
logger.debug("Releasing transactional SqlSession [" + session + "]");
     }
holder.released();


public void beforeCommit(boolean readOnly) 方法：

//10.session提交
if (TransactionSynchronizationManager.isActualTransactionActive()) {
                try {
                    if (logger.isDebugEnabled()) {
                        logger.debug("Transaction synchronization committing SqlSession [" + this.holder.getSqlSession() + "]");
                    }
                    this.holder.getSqlSession().commit();


public void afterCompletion(int status) 方法：

//11.解除事务绑定的session并关闭
            if (!this.holder.isOpen()) {
                TransactionSynchronizationManager.unbindResource(this.sessionFactory);
                try {
                    if (logger.isDebugEnabled()) {
                        logger.debug("Transaction synchronization closing SqlSession [" + this.holder.getSqlSession() + "]");
                    }
                    this.holder.getSqlSession().close();

 

在事务中，mybatis操作两个数据库的步骤流程：

1.创建SqlSession--第一个DAO，操作第一个DB

2.判断当前有事务

3.创建当前session的holder

4.将当前session的sessionFacotry的holder注册到事务中

5.执行sql。。。。

6.holder释放掉当前事务的session

7.当前在事务中，且sessionFactory的holder存在，则取得当前事务的session--第二个DAO，操作第二个DB

8.执行sql。。。。

9.释放掉当前事务的session

 

10.session提交

11.解除事务绑定的sessionFactory并关闭

 

可以知道在操作第二个DAO的时候取得的是，在事务中绑定的第一个SqlSession，整个Service用同一个SqlSession，所以无法切换数据源。

 

问题解决思路：通过上面的源代码

 

 

SqlSessionHolder holder = (SqlSessionHolder) TransactionSynchronizationManager.getResource(sessionFactory);


/4.将session的holder注册到事务中
TransactionSynchronizationManager.bindResource(sessionFactory, holder);
ransactionSynchronizationManager.registerSynchronization(new SqlSessionSynchronization(holder, sessionFactory));
           holder.setSynchronizedWithTransaction(true);

 

 

可以知道，事务绑定的是mybatis的当前SqlSessionFactory，如果SqlSessionFactory变了，则事务TransactionSynchronizationManager通过SqlSessionFactory（getResource(sessionFactory)）获取

的SqlSessionHolder必定不是上一个事务中的，即holder.isSynchronizedWithTransaction()为false。

由此，可以找出一个方法解决，动态切换SqlSessionFactory

OK，代码如下：

 

 

 

/**
 * 上下文Holder
 *
 */
@SuppressWarnings("unchecked")
public class ContextHolder<T> {

    private static final ThreadLocal contextHolder = new ThreadLocal();

    public static <T> void setContext(T context)
    {
        contextHolder.set(context);
    }

    public static <T> T getContext()
    {
        return (T) contextHolder.get();
    }

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

 

 

 

 

/**
 * 动态切换SqlSessionFactory的SqlSessionDaoSupport
 *
 * @see org.mybatis.spring.support.SqlSessionDaoSupport
 */
public class DynamicSqlSessionDaoSupport extends DaoSupport {

    private Map<Object, SqlSessionFactory> targetSqlSessionFactorys;

    private SqlSessionFactory              defaultTargetSqlSessionFactory;

    private SqlSession                     sqlSession;

    private boolean                        externalSqlSession;

    @Autowired(required = false)
    public final void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
        if (!this.externalSqlSession) {
            this.sqlSession = new SqlSessionTemplate(sqlSessionFactory);
        }
    }

    @Autowired(required = false)
    public final void setSqlSessionTemplate(SqlSessionTemplate sqlSessionTemplate) {
        this.sqlSession = sqlSessionTemplate;
        this.externalSqlSession = true;
    }

    /**
     * Users should use this method to get a SqlSession to call its statement
     * methods This is SqlSession is managed by spring. Users should not
     * commit/rollback/close it because it will be automatically done.
     *
     * @return Spring managed thread safe SqlSession
     */
    public final SqlSession getSqlSession() {
        SqlSessionFactory targetSqlSessionFactory = targetSqlSessionFactorys.get(ContextHolder
                .getContext());
        if (targetSqlSessionFactory != null) {
            setSqlSessionFactory(targetSqlSessionFactory);
        } else if (defaultTargetSqlSessionFactory != null) {
            setSqlSessionFactory(defaultTargetSqlSessionFactory);
        }
        return this.sqlSession;
    }

    /**
     * {@inheritDoc}
     */
    protected void checkDaoConfig() {
        Assert.notNull(this.sqlSession,
                "Property 'sqlSessionFactory' or 'sqlSessionTemplate' are required");
    }

    public Map<Object, SqlSessionFactory> getTargetSqlSessionFactorys() {
        return targetSqlSessionFactorys;
    }

    /**
     * Specify the map of target SqlSessionFactory, with the lookup key as key.
     * @param targetSqlSessionFactorys
     */
    public void setTargetSqlSessionFactorys(Map<Object, SqlSessionFactory> targetSqlSessionFactorys) {
        this.targetSqlSessionFactorys = targetSqlSessionFactorys;
    }

    public SqlSessionFactory getDefaultTargetSqlSessionFactory() {
        return defaultTargetSqlSessionFactory;
    }

    /**
     * Specify the default target SqlSessionFactory, if any.
     * @param defaultTargetSqlSessionFactory
     */
    public void setDefaultTargetSqlSessionFactory(SqlSessionFactory defaultTargetSqlSessionFactory) {
        this.defaultTargetSqlSessionFactory = defaultTargetSqlSessionFactory;
    }

}

 

 

 

//每一个DAO由继承SqlSessionDaoSupport全部改为DynamicSqlSessionDaoSupport
public class xxxDaoImpl extends DynamicSqlSessionDaoSupport implements xxxDao {

    public int insertUser(User user) {

        return this.getSqlSession().insert("xxx.xxxDao.insertUser", user);
    }

}

 

 

 

spring配置如下：

 

 

<!-- 创建数据源。 -->
    <bean id="ds1" class="org.springframework.jndi.JndiObjectFactoryBean">
        <property name="jndiName">
            <value>testxa</value>
        </property>
        <property name="resourceRef">
            <value>true</value>
        </property>
    </bean>
    <bean id="ds2" class="org.springframework.jndi.JndiObjectFactoryBean">
        <property name="jndiName">
            <value>testxa1</value>
        </property>
        <property name="resourceRef">
            <value>true</value>
        </property>
    </bean>


<!-- sqlSessionFactory工厂 -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="ds1" />
        <property name="configLocation" value="classpath:config/mybatis-config.xml" />
    </bean>
    <bean id="sqlSessionFactory1" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="ds2" />
        <property name="configLocation" value="classpath:config/mybatis-config.xml" />
    </bean>

<span style="white-space: pre;">    </span><!-- 动态切换SqlSessionFactory  -->
    <bean id="dynamicSqlSessionDaoSupport" class="com.suning.cmp.common.multidatasource.DynamicSqlSessionDaoSupport">
        <property name="targetSqlSessionFactorys">
            <map value-type="org.apache.ibatis.session.SqlSessionFactory">
                <entry key="ds1" value-ref="sqlSessionFactory" />
                <entry key="ds2" value-ref="sqlSessionFactory1" />
            </map>
        </property>
        <property name="defaultTargetSqlSessionFactory" ref="sqlSessionFactory" />
    </bean>

    <bean id="xxxDao" class="xxx.xxxDaoImpl" parent="dynamicSqlSessionDaoSupport"></bean>

 

 

 

Service测试代码如下：

 

 

@Transactional
    public void testXA() {

        ContextHolder.setContext("ds1");

        xxxDao.insertUser(user);


        ContextHolder.setContext("ds2");

        xxxDao.insertUser(user);


    }

 

 

 

通过Service代码，每个DAO访问都会调用getSqlSession()方法，此时就会调用DynamicSqlSessionDaoSupport的如下代码：

 

 

public final SqlSession getSqlSession() {
        SqlSessionFactory targetSqlSessionFactory = targetSqlSessionFactorys.get(ContextHolder
                .getContext());
        if (targetSqlSessionFactory != null) {
            setSqlSessionFactory(targetSqlSessionFactory);
        } else if (defaultTargetSqlSessionFactory != null) {
            setSqlSessionFactory(defaultTargetSqlSessionFactory);
        }
        return this.sqlSession;
    }

 

 

起到动态切换SqlSessionFactory（每一个SqlSessionFactory对应一个DB）。OK，到此圆满解决，动态切换和事务这两个问题。

在此，我补充下为什么到用到动态切换，其实每一个SqlSessionFactory对应一个DB，而关于此DB操作的所有DAO对应此SqlSessionFactory，在Service中不去切换，直接用对应不同SqlSessionFactory

的DAO也可以，此种方式可以参考附件：《Spring下mybatis多数据源配置》

问题就在于，项目中不同DB存在相同的Table，动态可以做到只配置一个DAO，且操作哪个DB是通过路由Routing或者通过什么获取才能知道（延迟到Service时才知道对应哪个DB），此种情况用到动态切换，就显得方便很多。。。