MyBatis源码解析之基础模块—Transaction

transaction
- jdbc
  - JdbcTransaction
  - JdbcTransactionFactory
- managed
  - ManagedTransaction
  - ManagedTransactionFactory
- DataSourceException
- TransactionFactory
- Transaction：

// Handles the connection lifecycle that comprises: its creation, preparation, commit/rollback and close.

/**
 * 处理整个连接生命周期的各种操作，包括连接创建，事务提交、回滚及连接关闭等数据库事务相关的操作。
 */
public interface Transaction {
​
  /** 获取数据库连接 */
  Connection getConnection() throws SQLException;
​
  /** 数据提交 */
  void commit() throws SQLException;
​
  /** 数据回滚 */
  void rollback() throws SQLException;
​
  /** 关闭数据库连接 */
  void close() throws SQLException;
​
  /** 获取超时时间，如果设置的话，Mybatis默认的两种实现，均设置为null */
  Integer getTimeout() throws SQLException;
}

package org.apache.ibatis.transaction;
​
import java.sql.Connection;
import java.util.Properties;
import javax.sql.DataSource;
import org.apache.ibatis.session.TransactionIsolationLevel;
​
/**
 * 事务创建工厂接口
 */
public interface TransactionFactory {
   */
  /** 设置相关配置信息 */
  default void setProperties(Properties props) {
    // NOP
  }
​
  /** 根据连接对象获取事务对象 */
  Transaction newTransaction(Connection conn);
​
  /**根据数据源、事务隔离级别、是否自动提交属性 构建事务对象*/
  Transaction newTransaction(DataSource dataSource, TransactionIsolationLevel level, boolean autoCommit);
}

package org.apache.ibatis.transaction.jdbc;
​
import java.sql.Connection;
import java.sql.SQLException;
import javax.sql.DataSource;
​
import org.apache.ibatis.logging.Log;
import org.apache.ibatis.logging.LogFactory;
import org.apache.ibatis.session.TransactionIsolationLevel;
import org.apache.ibatis.transaction.Transaction;
import org.apache.ibatis.transaction.TransactionException;
​
public class JdbcTransaction implements Transaction {
​
  private static final Log log = LogFactory.getLog(JdbcTransaction.class);
​
  protected Connection connection; //连接对象
  protected DataSource dataSource; //数据源
  protected TransactionIsolationLevel level;  //事务隔离级别
  protected boolean autoCommit; //是否自动提交
​
  public JdbcTransaction(DataSource ds, TransactionIsolationLevel desiredLevel, boolean desiredAutoCommit) {
    dataSource = ds;
    level = desiredLevel;
    autoCommit = desiredAutoCommit;
  }
​
  public JdbcTransaction(Connection connection) {
    this.connection = connection;
  }
​
  @Override
  public Connection getConnection() throws SQLException {
    if (connection == null) {
      openConnection();
    }
    return connection;
  }
​
  @Override
  public void commit() throws SQLException {
    if (connection != null && !connection.getAutoCommit()) {
      if (log.isDebugEnabled()) {
        log.debug("Committing JDBC Connection [" + connection + "]");
      }
      connection.commit();
    }
  }
​
  @Override
  public void rollback() throws SQLException {
    if (connection != null && !connection.getAutoCommit()) {
      if (log.isDebugEnabled()) {
        log.debug("Rolling back JDBC Connection [" + connection + "]");
      }
      connection.rollback();
    }
  }
​
  @Override
  public void close() throws SQLException {
    if (connection != null) {
      // 非自动提交情况下，设置为自动提交
      resetAutoCommit();
      if (log.isDebugEnabled()) {
        log.debug("Closing JDBC Connection [" + connection + "]");
      }
      // 关闭连接
      connection.close();
    }
  }
​
  protected void resetAutoCommit() {
    try {
      if (!connection.getAutoCommit()) {
        // MyBatis does not call commit/rollback on a connection if just selects were performed.
        // Some databases start transactions with select statements
        // and they mandate a commit/rollback before closing the connection.
        // A workaround is setting the autocommit to true before closing the connection.
        // Sybase throws an exception here.
        if (log.isDebugEnabled()) {
          log.debug("Resetting autocommit to true on JDBC Connection [" + connection + "]");
        }
        connection.setAutoCommit(true);
      }
    } catch (SQLException e) {
      if (log.isDebugEnabled()) {
        log.debug("Error resetting autocommit to true "
            + "before closing the connection.  Cause: " + e);
      }
    }
  }
​
  /**通过datasource获取数据库连接，然后属性level、autoCommit设置对应的事务隔离级别和是否自动提交*/
  protected void openConnection() throws SQLException {
    if (log.isDebugEnabled()) {
      log.debug("Opening JDBC Connection");
    }
    connection = dataSource.getConnection();
    if (level != null) {
      connection.setTransactionIsolation(level.getLevel());
    }
    setDesiredAutoCommit(autoCommit);
  }
  
  /** 设置是否自动提交 */
  protected void setDesiredAutoCommit(boolean desiredAutoCommit) {
    try {
      if (connection.getAutoCommit() != desiredAutoCommit) {
        if (log.isDebugEnabled()) {
          log.debug("Setting autocommit to " + desiredAutoCommit + " on JDBC Connection [" + connection + "]");
        }
        connection.setAutoCommit(desiredAutoCommit);
      }
    } catch (SQLException e) {
      // Only a very poorly implemented driver would fail here,
      // and there's not much we can do about that.
      throw new TransactionException("Error configuring AutoCommit.  "
        + "Your driver may not support getAutoCommit() or setAutoCommit(). "
        + "Requested setting: " + desiredAutoCommit + ".  Cause: " + e, e);
    }
  }
​
  @Override
  public Integer getTimeout() throws SQLException {
    return null;
  }
}

public class JdbcTransactionFactory implements TransactionFactory {
​
  /** 通过数据库连接获取事务 */
  @Override
  public Transaction newTransaction(Connection conn) {
    return new JdbcTransaction(conn);
  }
  /** 通过数据源、事务隔离级别、提交方式 获取事务 */
  @Override
  public Transaction newTransaction(DataSource ds, TransactionIsolationLevel level, boolean autoCommit) {
    return new JdbcTransaction(ds, level, autoCommit);
  }
}

public class ManagedTransaction implements Transaction {
​
  private static final Log log = LogFactory.getLog(ManagedTransaction.class);
​
  private DataSource dataSource; //数据源
  private TransactionIsolationLevel level; //事务隔离级别
  private Connection connection; //数据库连接
  private final boolean closeConnection; //是否关闭连接
​
  public ManagedTransaction(Connection connection, boolean closeConnection) {
    this.connection = connection;
    this.closeConnection = closeConnection;
  }
​
  public ManagedTransaction(DataSource ds, TransactionIsolationLevel level, boolean closeConnection) {
    this.dataSource = ds;
    this.level = level;
    this.closeConnection = closeConnection;
  }
​
  @Override
  public Connection getConnection() throws SQLException {
    if (this.connection == null) {
      openConnection();
    }
    return this.connection;
  }
​
  @Override
  public void commit() throws SQLException {
    // Does nothing
  }
​
  @Override
  public void rollback() throws SQLException {
    // Does nothing
  }
​
  @Override
  public void close() throws SQLException {
    // closeConnection 为true 且connection不为空时执行关闭
    if (this.closeConnection && this.connection != null) {
      if (log.isDebugEnabled()) {
        log.debug("Closing JDBC Connection [" + this.connection + "]");
      }
      this.connection.close();
    }
  }
​
  protected void openConnection() throws SQLException {
    if (log.isDebugEnabled()) {
      log.debug("Opening JDBC Connection");
    }
    this.connection = this.dataSource.getConnection();
    if (this.level != null) {
      this.connection.setTransactionIsolation(this.level.getLevel());
    }
  }
}