古い新人-「mybatisソースコードの読み取り-」トランザクショントランザクションモジュール

その他 2021-02-28 07:25:00 訪問数: null

I.概要

このモジュールはトランザクションに関するものです。私はコードを見ました。深くないのなら読んでみたらわかりますが、これで取引は実現するのでしょうか？いけませんか？どのようになります。もっと難しいのではないですか？これらは単純な実装だと思います。それは情事の巣であってはなりません。私たちの通常のプロジェクトでは、春に書かれた一連の事柄を使用する必要があります。とりあえず、まず何が起こっているのか見てみましょう。

パッケージの下にあるカテゴリの数を見てください

 

2：TransactionFactoryクラス

/**
 *    Copyright 2009-2020 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.transaction;

import java.sql.Connection;
import java.util.Properties;

import javax.sql.DataSource;

import org.apache.ibatis.session.TransactionIsolationLevel;

/**
 * Creates {@link Transaction} instances.
 *
 * @author Clinton Begin
 */
public interface TransactionFactory {

  /**
   * Sets transaction factory custom properties.
   *
   * 这个加了default 所以实现类可以实现也可以不实现。JdbcTransactionFactory就没有进行实现
   *
   * 设置工厂的属性
   *
   * @param props 属性
   */
  default void setProperties(Properties props) {
    // NOP
  }

  /**
   * Creates a {@link Transaction} out of an existing connection.
   * 创建 Transaction 事务
   *
   * @param conn Existing database connection
   * @return Transaction
   * @since 3.1.0
   */
  Transaction newTransaction(Connection conn);

  /**
   * Creates a {@link Transaction} out of a datasource.
   * 创建 Transaction 事务
   *
   * @param dataSource DataSource to take the connection from
   * @param level Desired isolation level
   * @param autoCommit Desired autocommit
   * @return Transaction
   * @since 3.1.0
   */
  Transaction newTransaction(DataSource dataSource, TransactionIsolationLevel level, boolean autoCommit);

}

JdbcTransactionFactory 类，就没有实现接口中的setProperties方法，代码如下
/**
 *    Copyright 2009-2019 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.transaction.jdbc;

import java.sql.Connection;

import javax.sql.DataSource;

import org.apache.ibatis.session.TransactionIsolationLevel;
import org.apache.ibatis.transaction.Transaction;
import org.apache.ibatis.transaction.TransactionFactory;

/**
 * Creates {@link JdbcTransaction} instances.
 * 创建实例 JdbcTransaction 的工厂类
 * @author Clinton Begin
 *
 * @see JdbcTransaction
 */
public class JdbcTransactionFactory implements TransactionFactory {

  @Override
  public Transaction newTransaction(Connection conn) {
    // 创建 JdbcTransaction 对象
    return new JdbcTransaction(conn);
  }

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

ManagedTransactionFactory 类，
/**
 *    Copyright 2009-2019 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.transaction.managed;

import java.sql.Connection;
import java.util.Properties;

import javax.sql.DataSource;

import org.apache.ibatis.session.TransactionIsolationLevel;
import org.apache.ibatis.transaction.Transaction;
import org.apache.ibatis.transaction.TransactionFactory;

/**
 * Creates {@link ManagedTransaction} instances.
 *
 * @author Clinton Begin
 *
 * @see ManagedTransaction
 */
public class ManagedTransactionFactory implements TransactionFactory {
  /**
   * 是否关闭连接
   */
  private boolean closeConnection = true;

  @Override
  public void setProperties(Properties props) {
    // 获得是否关闭连接属性
    if (props != null) {
      String closeConnectionProperty = props.getProperty("closeConnection");
      if (closeConnectionProperty != null) {
        closeConnection = Boolean.parseBoolean(closeConnectionProperty);
      }
    }
  }

  @Override
  public Transaction newTransaction(Connection conn) {
    // 创建 ManagedTransaction 对象
    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.
    //静默忽略autocommit和隔离级别，因为托管事务是完全的
    //由外部管理者控制。它被无声地忽略了
    //代码在托管和非托管配置之间保持可移植性。
    return new ManagedTransaction(ds, level, closeConnection);
  }
}

TransactionFactory 和2个实现类的代码就是这么简单。说这个叫什么模式呢，工厂模式吗？我感觉不像，我也不知道他是什么鬼模式，反正代码先是这个样，等我以后知道了。再来补充

3：トランザクションインターフェイスとその実装クラスJdbcTransaction、ManagedTransaction

トランザクションコードは次のとおりです。

/**
 *    Copyright 2009-2020 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.transaction;

import java.sql.Connection;
import java.sql.SQLException;

/**
 * Wraps a database connection.
 * Handles the connection lifecycle that comprises: its creation, preparation, commit/rollback and close.
 *
 * 封装数据库连接。
 * 处理连接生命周期，包括:它的创建，准备，提交/回滚和关闭
 * @author Clinton Begin
 */
public interface Transaction {

  /**
   * Retrieve inner database connection.
   * 连接相关-》获得连接
   *
   * @return DataBase connection
   * @throws SQLException
   *           the SQL exception
   */
  Connection getConnection() throws SQLException;
  /**
   * 连接相关-》关闭连接
   * Close inner database connection.
   * @throws SQLException
   *           the SQL exception
   */
  void close() throws SQLException;

  /**
   * 事务相关-》事务提交
   *
   * Commit inner database connection.
   * @throws SQLException
   *           the SQL exception
   */
  void commit() throws SQLException;

  /**
   *  事务相关-》事务回滚
   *
   *  只能回滚未提交的事务
   * Rollback inner database connection.
   * @throws SQLException
   *           the SQL exception
   */
  void rollback() throws SQLException;

  /**
   * 事务相关-》获得事务超时时间
   *
   * Get transaction timeout if set.
   *
   * @return the timeout
   * @throws SQLException
   *           the SQL exception
   */
  Integer getTimeout() throws SQLException;

}

JdbcTransaction 类，这个类的close方法值得关注和思考。这个方法里面的Connection connection对象是代理对象还是真实的数据库连接对象。要想明白。我想了好一会。我嘛，比较菜。
/**
 *    Copyright 2009-2020 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
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;

/**
 * {@link Transaction} that makes use of the JDBC commit and rollback facilities directly.
 * It relies on the connection retrieved from the dataSource to manage the scope of the transaction.
 * Delays connection retrieval until getConnection() is called.
 * Ignores commit or rollback requests when autocommit is on.
 *
 * 它直接使用JDBC提交和回滚功能。
 * *依赖于从数据源检索到的连接来管理事务的范围。
 * *延迟连接检索，直到getConnection()被调用。
 * *当自动提交时忽略提交或回滚请求。
 * @author Clinton Begin
 *
 * @see JdbcTransactionFactory
 */
public class JdbcTransaction implements Transaction {

  private static final Log log = LogFactory.getLog(JdbcTransaction.class);
  /**
   * Connection 对象
   */
  protected Connection connection;
  /**
   * DataSource 对象
   */
  protected DataSource dataSource;
  /**
   * 事务隔离级别
   */
  protected TransactionIsolationLevel level;
  /**
   * 是否自动提交
   */
  protected boolean autoCommit;

  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 {
    // 连接为空，进行创建
    if (connection == null) {
      openConnection();
    }
    return connection;
  }

  @Override
  public void commit() throws SQLException {
    // 非自动提交的事务，则可以提交事务
    if (connection != null && !connection.getAutoCommit()) {
      if (log.isDebugEnabled()) {
        log.debug("Committing JDBC Connection [" + connection + "]");
      }
      connection.commit();
    }
  }

  @Override
  public void rollback() throws SQLException {
    // 非自动提交的事务，则可以回滚事务
    if (connection != null && !connection.getAutoCommit()) {
      if (log.isDebugEnabled()) {
        log.debug("Rolling back JDBC Connection [" + connection + "]");
      }
      connection.rollback();
    }
  }

  /**
   * 连接要关闭了。为啥要重置自动提交呢？ todo
   * 数据源使用的是线程池PooledDataSource：
   * 如果使用了连接池，也就是使用了PooledDataSource 里面的getConnection方法，那么获取到的连接就是一个代理对象
   * 代理对象中。PooledConnection 类的invoke方法会对关闭进行拦截。会调用pushConnection方法。
   * 这个方法在DataSource模块有说过的，这个方法就是把连接放到闲置的连接池中去。那么我们把这个自动提交进行重置就是正确的。因为害怕下次取的连接这个属性被设置过。
   *
   * 数据源使用的是 “非” 线程池PooledDataSource：
   * 那么connection.close() 就是直接调用数据库中的关闭方法了。那么就算设置了自动提交，其实也无所谓的。
   *
   * @throws SQLException 异常。
   */
  @Override
  public void close() throws SQLException {
    if (connection != null) {
      // 重置为自动提交
      resetAutoCommit();
      if (log.isDebugEnabled()) {
        log.debug("Closing JDBC Connection [" + connection + "]");
      }
      // 关闭连接
      connection.close();
    }
  }

  /**
   * 设置指定的 autoCommit 属性
   *
   * @param desiredAutoCommit 是否自动提交的标识
   */
  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);
    }
  }

  /**
   * 重置为自动提交。
   */
  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);
      }
    }
  }

  protected void openConnection() throws SQLException {
    if (log.isDebugEnabled()) {
      log.debug("Opening JDBC Connection");
    }
    // 从数据库中获取连接
    connection = dataSource.getConnection();
    if (level != null) {
      // 设置事务的级别
      connection.setTransactionIsolation(level.getLevel());
    }
    // 设置自动提交
    setDesiredAutoCommit(autoCommit);
  }

  @Override
  public Integer getTimeout() throws SQLException {
    return null;
  }

}

ManagedTransaction 这个类里面干的事更少了。我就不相信这个类，单纯就靠这个类能实现事务。我认为这个肯定也只是个外壳。如果我以后看到了。会回来补充的。todo
/**
 *    Copyright 2009-2020 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.transaction.managed;

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;

/**
 * {@link Transaction} that lets the container manage the full lifecycle of the transaction.
 * 让容器管理事务的整个生命周期
 * Delays connection retrieval until getConnection() is called.
 * 延迟连接检索，直到getConnection()被调用
 * Ignores all commit or rollback requests.
 *忽略所有提交或回滚请求
 * By default, it closes the connection but can be configured not to do it.
 * 默认情况下，它关闭连接，但可以配置不这样做。
 * @author Clinton Begin
 *
 * @see ManagedTransactionFactory
 */
public class ManagedTransaction implements Transaction {

  private static final Log log = LogFactory.getLog(ManagedTransaction.class);
  /**
   * DataSource 对象
   */
  private DataSource dataSource;
  /**
   * 事务隔离级别
   */
  private TransactionIsolationLevel level;
  /**
   * Connection 对象
   */
  private Connection connection;
  /**
   * 是否关闭连接
   *
   * 这个属性是和 {@link org.apache.ibatis.transaction.jdbc.JdbcTransaction} 不同的
   */
  private final boolean closeConnection;

  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 {
    // 连接为空，进行创建
    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 {
    // 如果开启关闭连接功能，则关闭连接
    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");
    }
    // 获得连接
    this.connection = this.dataSource.getConnection();
    // 设置隔离级别
    if (this.level != null) {
      this.connection.setTransactionIsolation(this.level.getLevel());
    }
  }

  @Override
  public Integer getTimeout() throws SQLException {
    return null;
  }

}

4：まとめ

 私は将来自分自身に答えます

ManagedTransactionクラスは単純すぎます。このように物事を成し遂げることは不可能だと思います。追加するために戻ってきたい。

TransactionFactoryインターフェースの下には2つの実装クラスがあります。シンプルなインターフェイスであり、複数の実装であり、デザインパターンではないと思います。デザインパターンはまだ見たことがなく、デザインパターンについても深く理解していません。私はそれを理解するまでこの質問を続けたいと思います。追加するために戻ってきます

結論として

  1.  このパッケージでは、考慮する必要があるのはJdbcTransactionクラスだけです。このクラスのcloseメソッドは注意と検討に値するものであり、他のコードは比較的単純です。
  2. OK！仕事の初日。作業を終了しました。私はこのブログを書くために残業しました。お役に立てば幸いです。あなたが私のようなら。いくつかの料理が、和解していません。

次のプレビュー：キャッシュパッケージコードの読み取り。

 

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