mybatis--MapperProxy事务

上篇详细分析了org.mybatis.spring.mapper.MapperScannerConfigurer 和 org.mybatis.spring.SqlSessionFactoryBean的作用，可以直接看最后的总结

MapperFactoryBean是mapper接口的入口，它包含了sqlSessionFactory的封装SqlSessionTemplate，而sqlSessionFactory又包含了mapper xml的组装Configuration对象

从SqlSessionTemplate的

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

开始，进入Configuration的getMapper(type,sqlsession)

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {    return this.mapperRegistry.getMapper(type, sqlSession);}

进入MapperRegistry

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {    MapperProxyFactory mapperProxyFactory = (MapperProxyFactory)this.knownMappers.get(type);    if(mapperProxyFactory == null) {        throw new BindingException("Type " + type + " is not known to the MapperRegistry.");    } else {        try {            return mapperProxyFactory.newInstance(sqlSession);        } catch (Exception var5) {            throw new BindingException("Error getting mapper instance. Cause: " + var5, var5);        }    }}

由MapperProxyFactory生成代理MapperProxy

protected T newInstance(MapperProxy<T> mapperProxy) {    return Proxy.newProxyInstance(this.mapperInterface.getClassLoader(), new Class[]{this.mapperInterface}, mapperProxy);}

public T newInstance(SqlSession sqlSession) {    MapperProxy mapperProxy = new MapperProxy(sqlSession, this.mapperInterface, this.methodCache);    return this.newInstance(mapperProxy);}

所以最终的调用会进入MapperProxy，接下来几步在 mybatis缓存中有介绍，会调用sqlSession（实际是SqlSessionTemplate）中的方法，看构造方法：

public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) {Assert.notNull(sqlSessionFactory, "Property \'sqlSessionFactory\' is required");Assert.notNull(executorType, "Property \'executorType\' is required");this.sqlSessionFactory = sqlSessionFactory;this.executorType = executorType;this.exceptionTranslator = exceptionTranslator;this.sqlSessionProxy = (SqlSession)Proxy.newProxyInstance(SqlSessionFactory.class.getClassLoader(), new Class[]{SqlSession.class}, new SqlSessionTemplate.SqlSessionInterceptor());}

会对SqlSessionFactory生成代理，实际调用这个代理的方法

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

1. 进入SqlSessionTemplate.SqlSessionInterceptor

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {    SqlSession sqlSession = SqlSessionUtils.getSqlSession(SqlSessionTemplate.this.sqlSessionFactory, SqlSessionTemplate.this.executorType, SqlSessionTemplate.this.exceptionTranslator);　　 ......    Object t = method.invoke(sqlSession, args);    ......}

看SqlSessionUtils.getSqlSession方法：

public static SqlSession getSqlSession(SqlSessionFactory sessionFactory, ExecutorType executorType, PersistenceExceptionTranslator exceptionTranslator) {Assert.notNull(sessionFactory, "No SqlSessionFactory specified");Assert.notNull(executorType, "No ExecutorType specified");SqlSessionHolder holder = (SqlSessionHolder)TransactionSynchronizationManager.getResource(sessionFactory);if(holder != null && holder.isSynchronizedWithTransaction()) {if(holder.getExecutorType() != executorType) {throw new TransientDataAccessResourceException("Cannot change the ExecutorType when there is an existing transaction");} else {holder.requested();if(logger.isDebugEnabled()) {logger.debug("Fetched SqlSession [" + holder.getSqlSession() + "] from current transaction");}return holder.getSqlSession();}} else {//进入这里呀呀呀if(logger.isDebugEnabled()) {logger.debug("Creating a new SqlSession");}
　　　　　　　//step 1.1SqlSession session = sessionFactory.openSession(executorType);if(TransactionSynchronizationManager.isSynchronizationActive()) {Environment environment = sessionFactory.getConfiguration().getEnvironment();if(environment.getTransactionFactory() instanceof SpringManagedTransactionFactory) {if(logger.isDebugEnabled()) {logger.debug("Registering transaction synchronization for SqlSession [" + session + "]");}//step 1.2holder = new SqlSessionHolder(session, executorType, exceptionTranslator);TransactionSynchronizationManager.bindResource(sessionFactory, holder);TransactionSynchronizationManager.registerSynchronization(new SqlSessionUtils.SqlSessionSynchronization(holder, sessionFactory));holder.setSynchronizedWithTransaction(true);holder.requested();} else {if(TransactionSynchronizationManager.getResource(environment.getDataSource()) != null) {throw new TransientDataAccessResourceException("SqlSessionFactory must be using a SpringManagedTransactionFactory in order to use Spring transaction synchronization");}if(logger.isDebugEnabled()) {logger.debug("SqlSession [" + session + "] was not registered for synchronization because DataSource is not transactional");}}} else if(logger.isDebugEnabled()) {logger.debug("SqlSession [" + session + "] was not registered for synchronization because synchronization is not active");}return session;}}

1.1 进入DefaultSqlSessionFactory openSession方法：

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {Transaction tx = null;DefaultSqlSession var8;try {Environment e = this.configuration.getEnvironment();//springManagedTransactionFactoryTransactionFactory transactionFactory = this.getTransactionFactoryFromEnvironment(e);tx = transactionFactory.newTransaction(e.getDataSource(), level, autoCommit);Executor executor = this.configuration.newExecutor(tx, execType, autoCommit);var8 = new DefaultSqlSession(this.configuration, executor);} catch (Exception var12) {this.closeTransaction(tx);throw ExceptionFactory.wrapException("Error opening session.  Cause: " + var12, var12);} finally {ErrorContext.instance().reset();}return var8;}

进入SpringManagedTransactionFactory的

newTransaction(e.getDataSource(), level, autoCommit);

return new SpringManagedTransaction(dataSource);

这个SpringManagedTransaction比较特别，因为

private void openConnection() throws SQLException {    this.connection = DataSourceUtils.getConnection(this.dataSource);    this.autoCommit = this.connection.getAutoCommit();    this.isConnectionTransactional = DataSourceUtils.isConnectionTransactional(this.connection, this.dataSource);    if(this.logger.isDebugEnabled()) {        this.logger.debug("JDBC Connection [" + this.connection + "] will" + (this.isConnectionTransactional?" ":" not ") + "be managed by Spring");    }}

因为它的连接来自DataSourceUtils

public static Connection doGetConnection(DataSource dataSource) throws SQLException {Assert.notNull(dataSource, "No DataSource specified");ConnectionHolder conHolder = (ConnectionHolder)TransactionSynchronizationManager.getResource(dataSource);if(conHolder == null || !conHolder.hasConnection() && !conHolder.isSynchronizedWithTransaction()) {logger.debug("Fetching JDBC Connection from DataSource");Connection con = dataSource.getConnection();if(TransactionSynchronizationManager.isSynchronizationActive()) {logger.debug("Registering transaction synchronization for JDBC Connection");ConnectionHolder holderToUse = conHolder;if(conHolder == null) {holderToUse = new ConnectionHolder(con);} else {conHolder.setConnection(con);}holderToUse.requested();TransactionSynchronizationManager.registerSynchronization(new DataSourceUtils.ConnectionSynchronization(holderToUse, dataSource));holderToUse.setSynchronizedWithTransaction(true);if(holderToUse != conHolder) {TransactionSynchronizationManager.bindResource(dataSource, holderToUse);}}return con;} else {conHolder.requested();if(!conHolder.hasConnection()) {logger.debug("Fetching resumed JDBC Connection from DataSource");conHolder.setConnection(dataSource.getConnection());}return conHolder.getConnection();}}

这一步就和 spring--事务原理中分析的对接了！！！connection连接对象来自当前线程绑定的ConnectionHolder中的connection对象

最终 DefaultSqlSession-》Executor-》Transaction-》当前线程绑定的ConnectionHolder中的connection对象

1.2 构建SqlSessionHolder-》DefaultSqlSession，并绑定到当前线程<sessionFactory,session holder>

2. DefaultSqlSession的执行见 mybatis缓存

转载于:https://www.cnblogs.com/yhzh/p/5588390.html

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