spring的jdbc和mybatis

引用：由于JdbcTemplate、NamedParameterJdbcTemplate、SimpleJdbcTemplate类使用DataSourceUtils获取及释放连接，而且连接是与线程绑定的，因此这些JDBC模板类是线程安全的，即JdbcTemplate对象可以在多线程中重用。

 

spring的JDBC：

DataSourceUtils得到一个数据库连接的实现，和hibernate等ORM框架一样，得到连接后放入ThreadLocal中，同一个线程用同一个连接，源码如下：

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())) {
			conHolder.requested();
			if (!conHolder.hasConnection()) {
				logger.debug("Fetching resumed JDBC Connection from DataSource");
				conHolder.setConnection(dataSource.getConnection());
			}
			return conHolder.getConnection();
		}
		// Else we either got no holder or an empty thread-bound holder here.

		logger.debug("Fetching JDBC Connection from DataSource");
		Connection con = dataSource.getConnection();

		if (TransactionSynchronizationManager.isSynchronizationActive()) {
			logger.debug("Registering transaction synchronization for JDBC Connection");
			// Use same Connection for further JDBC actions within the transaction.
			// Thread-bound object will get removed by synchronization at transaction completion.
			ConnectionHolder holderToUse = conHolder;
			if (holderToUse == null) {
				holderToUse = new ConnectionHolder(con);
			}
			else {
				holderToUse.setConnection(con);
			}
			holderToUse.requested();
			TransactionSynchronizationManager.registerSynchronization(
					new ConnectionSynchronization(holderToUse, dataSource));
			holderToUse.setSynchronizedWithTransaction(true);
			if (holderToUse != conHolder) {
				TransactionSynchronizationManager.bindResource(dataSource, holderToUse);
			}
		}

		return con;
	}

 其中，获取到一个数据库连接后，放入一个事务中并放入ThreadLocal，源码如下：

private static final ThreadLocal<Set<TransactionSynchronization>> synchronizations =
			new NamedThreadLocal<Set<TransactionSynchronization>>("Transaction synchronizations");

//...

public static void registerSynchronization(TransactionSynchronization synchronization)
			throws IllegalStateException {

		Assert.notNull(synchronization, "TransactionSynchronization must not be null");
		if (!isSynchronizationActive()) {
			throw new IllegalStateException("Transaction synchronization is not active");
		}
		synchronizations.get().add(synchronization);
	}

 

MyBites:

1）我们在配置文件中，一般这么配置，但是只是获取读取解析配置session工厂的一个bean，该bean其中一个属性为SqlSessionFactory sqlSessionFactory;即session工厂，通过该对象可获得一个数据库连接：

配置文件：

 

<!-- spring和MyBatis完美整合，不需要mybatis的配置映射文件 ,自动扫描加载Sql映射文件/接口-->  
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">  
        <property name="dataSource" ref="dataSource" />  
        <!-- 自动扫描mapping.xml文件 -->  
        <property name="mapperLocations" value="classpath:mapping/*.xml"></property>  
    </bean> 

 在mybatis中，session工厂的默认实现为DefaultSqlSessionFactory类：

 

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
      final Environment environment = configuration.getEnvironment();
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      final Executor executor = configuration.newExecutor(tx, execType);
      return new DefaultSqlSession(configuration, executor, autoCommit);
    } catch (Exception e) {
      closeTransaction(tx); // may have fetched a connection so lets call close()
      throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

 2）其中，获取数据库连接，仍然是用底层rt.jar的DataSource，具体要看配置的事务类型TransactionFactory，比如下面这种，就是使用spring本身的，即DataSourceUtils的。

 

<bean id="txManager"  
        class="org.springframework.jdbc.datasource.DataSourceTransactionManager">  
        <property name="dataSource" ref="dataSource" />  
    </bean> 

mybatis中，可以使用三种处理事务类型，如下图，前两种是mybatis本身封装的，使用原生的rt.jar中DataSource获取数据库连接。

 3）session中的Executor executor，也有三种实现（BatchExecutor批量执行、ClosedExecutor、ReuseExecutor、SimpleExecutor），如下图，但都会继承BaseExecutor这个基本类，具体属性之后再看，待续.......