【源码】Mybatis（二）

上一篇简单介绍了获取SqlSessionFactory的源码，最后是创建了一个DefaultSqlSessionFactory。这篇来看看DefaultSqlSessionFactory具体都做了些什么。

package org.apache.ibatis.session.defaults;

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

import org.apache.ibatis.exceptions.ExceptionFactory;
import org.apache.ibatis.executor.ErrorContext;
import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.mapping.Environment;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.ExecutorType;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.TransactionIsolationLevel;
import org.apache.ibatis.transaction.Transaction;
import org.apache.ibatis.transaction.TransactionFactory;
import org.apache.ibatis.transaction.managed.ManagedTransactionFactory;

/**
 * @author Clinton Begin
 */
//默认SqlSession工厂
public class DefaultSqlSessionFactory implements SqlSessionFactory {

  private final Configuration configuration;//从配置文件中读取的数据都存放在configuration对象里

  public DefaultSqlSessionFactory(Configuration configuration) {
    this.configuration = configuration;
  }

  @Override
  public SqlSession openSession() {//创建SqlSession的默认方法，false代表事务非自动提交
    return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
  }

  @Override
  public SqlSession openSession(boolean autoCommit) {//可以声明事务自动提交
    return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, autoCommit);
  }

  @Override
  public SqlSession openSession(ExecutorType execType) {//可选择ExecutorType，包括SimpleExecutor、BatchExecutor、ReuseExecutor三种
    return openSessionFromDataSource(execType, null, false);
  }

  @Override
  public SqlSession openSession(TransactionIsolationLevel level) {//可选择事务隔离级别
    return openSessionFromDataSource(configuration.getDefaultExecutorType(), level, false);
  }

  //下面的构造器都是大同小异
  @Override
  public SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level) {
    return openSessionFromDataSource(execType, level, false);
  }

  @Override
  public SqlSession openSession(ExecutorType execType, boolean autoCommit) {
    return openSessionFromDataSource(execType, null, autoCommit);
  }

  @Override
  public SqlSession openSession(Connection connection) {
    return openSessionFromConnection(configuration.getDefaultExecutorType(), connection);
  }

  @Override
  public SqlSession openSession(ExecutorType execType, Connection connection) {
    return openSessionFromConnection(execType, connection);
  }

  @Override
  public Configuration getConfiguration() {
    return configuration;
  }

  private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
      //获取transactionManager和dataSource信息
      final Environment environment = configuration.getEnvironment();
      /*事务工厂，如果配置文件里没有配置则返回ManagedTransactionFactory，可配置“JDBC”，返回JdbcTransactionFactory*/
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      //创建transaction，因为在配置文件里配置了JDBC，所以返回JdbcTransaction。JdbcTransaction里面注入了DataSource等信息。
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      //创建Executor，SQL执行器，注入tx和execType，如果配置了cache，则返回CachingExecutor。
      final Executor executor = configuration.newExecutor(tx, execType);
      return new DefaultSqlSession(configuration, executor, autoCommit);//返回DefaultSqlSession
    } 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();
    }
  }

  //与上面方法类似，上面创建Transaction通过拿DataSource的数据，这里直接传入Connection
  private SqlSession openSessionFromConnection(ExecutorType execType, Connection connection) {
    try {
      boolean autoCommit;
      try {
        autoCommit = connection.getAutoCommit();
      } catch (SQLException e) {
        // Failover to true, as most poor drivers
        // or databases won't support transactions
        autoCommit = true;
      }
      final Environment environment = configuration.getEnvironment();
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      final Transaction tx = transactionFactory.newTransaction(connection);
      final Executor executor = configuration.newExecutor(tx, execType);
      return new DefaultSqlSession(configuration, executor, autoCommit);
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

  private TransactionFactory getTransactionFactoryFromEnvironment(Environment environment) {
    if (environment == null || environment.getTransactionFactory() == null) {
      return new ManagedTransactionFactory();
    }
    return environment.getTransactionFactory();
  }

  private void closeTransaction(Transaction tx) {
    if (tx != null) {
      try {
        tx.close();
      } catch (SQLException ignore) {
        // Intentionally ignore. Prefer previous error.
      }
    }
  }

}

总结

DefaultSqlSessionFactory主要的作用就是来创建SqlSession的，通过Configuration里面的数据，组装TransactionFactory，通过TransactionFactory创建Transaction，再将这些数据组装成Executor，最后组装成DefaultSqlSession。至此SqlSession创建成功。

源码来自Mybatis3.5.0版本。