《Mybatis源码》第15章 Transaction

事务工厂(TransactionFactory)

TransactionFactory该接口有2个子类JdbcTransactionFactory 和 ManagedTransactionFactory，分别代表JDBC类型 和 MANAGED类型

JdbcTransactionFactory 生产JdbcTransaction，会使用Connection对象的commit()、rollback()、close()方法来管理方法

ManagedTransactionFactory生产ManagedTransaction，会把事务交给容器去管理

TransactionFactory

public interface TransactionFactory {

  void setProperties(Properties props);
    
  // 通过连接创建事务对象
  Transaction newTransaction(Connection conn);
    
  // 通过数据源创建事务对象
  Transaction newTransaction(DataSource dataSource, TransactionIsolationLevel level, boolean autoCommit);
    
}

JdbcTransactionFactory

public class JdbcTransactionFactory implements TransactionFactory {

  @Override
  public void setProperties(Properties props) {
  }

  @Override
  public Transaction newTransaction(Connection conn) {
    // 创建JdbcTransaction类型的事务
    return new JdbcTransaction(conn);
  }

  @Override
  public Transaction newTransaction(DataSource ds, TransactionIsolationLevel level, boolean autoCommit) {
    return new JdbcTransaction(ds, level, autoCommit);
  }
}

ManagedTransactionFactory

public class ManagedTransactionFactory implements TransactionFactory {

  private boolean closeConnection = true;

  @Override
  public void setProperties(Properties props) {
    if (props != null) {
      String closeConnectionProperty = props.getProperty("closeConnection");
      if (closeConnectionProperty != null) {
        closeConnection = Boolean.valueOf(closeConnectionProperty);
      }
    }
  }

  @Override
  public Transaction newTransaction(Connection conn) {
    // 创建ManagedTransaction类型的事务
    return new ManagedTransaction(conn, closeConnection);
  }

  @Override
  public Transaction newTransaction(DataSource ds, TransactionIsolationLevel level, boolean autoCommit) {
    // Silently ignores autocommit and isolation level, as managed transactions are entirely
    // controlled by an external manager.  It's silently ignored so that
    // code remains portable between managed and unmanaged configurations.
    return new ManagedTransaction(ds, level, closeConnection);
  }
}

事务(Transaction)

Transaction

上面看到了对象工厂创建了Transaction类，那么接下来看一下，Transaction接口有2个子类JdbcTransaction 和 ManagedTransaction，也就是刚才两个工厂负责创建的

// 方法一看就能看得懂
public interface Transaction {
  
  Connection getConnection() throws SQLException;

  void commit() throws SQLException;

  void rollback() throws SQLException;

  void close() throws SQLException;

  Integer getTimeout() throws SQLException;
  
}

JdbcTransaction

JdbcTransaction，这里面的commit、rollback方法就重写了，仔细看一下，似乎长得一样，都是判断是否自动提交，然后通过连接去执行方法

public class JdbcTransaction implements Transaction {
  @Override
  public void commit() throws SQLException {
    // 验证连接 && 是否自动提交
    if (connection != null && !connection.getAutoCommit()) {
      if (log.isDebugEnabled()) {
        log.debug("Committing JDBC Connection [" + connection + "]");
      }
      connection.commit();
    }
  }

  @Override
  public void rollback() throws SQLException {
    // 验证连接 && 是否自动
    if (connection != null && !connection.getAutoCommit()) {
      if (log.isDebugEnabled()) {
        log.debug("Rolling back JDBC Connection [" + connection + "]");
      }
      connection.rollback();
    }
  }
}

ManagedTransaction

ManagedTransaction含义为托管事务，空壳事务管理器，皮包公司。仅是提醒用户，在其它环境中应用时，把事务托管给其它框架，比如托管给Spring，让Spring去管理事务，从源码中我们看到 commit 和 rollback 都是空实现

public class ManagedTransaction implements Transaction {
  // 省略一些....
    
  @Override
  public void commit() throws SQLException {
    // Does nothing
  }

  @Override
  public void rollback() throws SQLException {
    // Does nothing
  }
  
  // 省略一些....
}