mybatis之spring对事务的处理

短命女 2022-09-10 02:27 4阅读 0赞

## 写在前面 ##

这里[这篇文章][Link 1]分析了spring封装mybaits的SqlSession的`org.mybatis.spring.SqlSessionTemplate`对象，但是其中事务相关内容并没有深入探究，本文作为补充来看下。在阅读本文之前，先通过[这篇文章][Link 2]看下mybatis对于事务抽象的相关API。  
在`mybaits-spring`中针对事务接口`org.apache.ibatis.transaction.Transaction`接口提供的针对spring环境中事务管理的实现类是`org.ibatis.spring.transaction.SpringManagedTransaction`，我们就从该类开始分析。

## 1：SpringManagedTransaction ##

源码如下：

org.mybatis.spring.transaction.SpringManagedTransaction
    /** * {@code SpringManagedTransaction} handles the lifecycle of a JDBC connection. * It retrieves a connection from Spring's transaction manager and returns it back to it * when it is no longer needed. * <p> * If Spring's transaction handling is active it will no-op all commit/rollback/close calls * assuming that the Spring transaction manager will do the job. * <p> * If it is not it will behave like {@code JdbcTransaction}. * * @author Hunter Presnall * @author Eduardo Macarron */
    // spring环境中管理JDBC连接，会spring的事务管理器中获取一个连接，在不使用的时候归还给数据库连接器
    //,
    public class SpringManagedTransaction implements Transaction { 
    
      private static final Log LOGGER = LogFactory.getLog(SpringManagedTransaction.class);
    
      private final DataSource dataSource;
    
      private Connection connection;
    
      private boolean isConnectionTransactional;
    
      private boolean autoCommit;
    
      public SpringManagedTransaction(DataSource dataSource) { 
        notNull(dataSource, "No DataSource specified");
        this.dataSource = dataSource;
      }
    
      @Override
      public Connection getConnection() throws SQLException { 
        if (this.connection == null) { 
          openConnection();
        }
        return this.connection;
      }
    
      // 从spring的事务管理器中获取连接
      private void openConnection() throws SQLException { 
        // 通过spring的DaSourceUtils工具类获取连接对象
        this.connection = DataSourceUtils.getConnection(this.dataSource);
        // 获取是否自动提交
        this.autoCommit = this.connection.getAutoCommit();
        // 是否为事务连接，如果是则说明是被spring管理的，否则不是被spring管理的
        this.isConnectionTransactional = DataSourceUtils.isConnectionTransactional(this.connection, this.dataSource);
    
        if (LOGGER.isDebugEnabled()) { 
          LOGGER.debug(
              "JDBC Connection ["
                  + this.connection
                  + "] will"
                  + (this.isConnectionTransactional ? " " : " not ")
                  + "be managed by Spring");
        }
      }
    
      @Override
      public void commit() throws SQLException { 
    	// 如果不是被spring事务管理器管理的，则在此处提交，否则不操作
        if (this.connection != null && !this.isConnectionTransactional && !this.autoCommit) { 
          if (LOGGER.isDebugEnabled()) { 
            LOGGER.debug("Committing JDBC Connection [" + this.connection + "]");
          }
          // 直接提交事务
          this.connection.commit();
        }
      }
    
      @Override
      public void rollback() throws SQLException { 
    	// 如果不是被spring事务管理器管理的，则回滚，否则此处不操作
        if (this.connection != null && !this.isConnectionTransactional && !this.autoCommit) { 
          if (LOGGER.isDebugEnabled()) { 
            LOGGER.debug("Rolling back JDBC Connection [" + this.connection + "]");
          }
          // 回滚
          this.connection.rollback();
        }
      }
    
      @Override
      public void close() throws SQLException { 
    	// 关闭连接
        DataSourceUtils.releaseConnection(this.connection, this.dataSource);
      }
    
      @Override
      public Integer getTimeout() throws SQLException { 
        ConnectionHolder holder = (ConnectionHolder) TransactionSynchronizationManager.getResource(dataSource);
        if (holder != null && holder.hasTimeout()) { 
          return holder.getTimeToLiveInSeconds();
        } 
        return null;
      }
    
    }

对应的工厂类是`org.mybatis.spring.transaction.SpringManagedTransactionFactory`具体参考`2：SpringManagedTransactionFactory`。

## 2：SpringManagedTransactionFactory ##

源码如下：

// 创建SpringManagedTransaction实例的工厂类
    public class SpringManagedTransactionFactory implements TransactionFactory { 
    
      @Override
      public Transaction newTransaction(DataSource dataSource, TransactionIsolationLevel level, boolean autoCommit) { 
        return new SpringManagedTransaction(dataSource);
      }
    
      @Override
      public Transaction newTransaction(Connection conn) { 
        throw new UnsupportedOperationException("New Spring transactions require a DataSource");
      }
    
      @Override
      public void setProperties(Properties props) { 
        // not needed in this version
      }
    
    }

[Link 1]: https://blog.csdn.net/wang0907/article/details/120081717
[Link 2]: https://blog.csdn.net/wang0907/article/details/120095257