SqlSession最常用的类

http://chengjisihan.iteye.com/blog/752168(SqlSession,SqlSessionFactory,SqlSessionFactoryBuilder,Environment,Configuration,Mapper)

http://chengjisihan.iteye.com/blog/755104(Interceptor,TypeHandler,ObjectFactory,TypeAlias,SelectBuilder)

http://chengjisihan.iteye.com/blog/760259（Dynamic SQL)

SqlSession中的几个方法在Dao中经常要用到。。
SqlSessionFactory是用来构造SqlSession的

public interface SqlSessionFactory {

  SqlSession openSession();

  SqlSession openSession(boolean autoCommit);
  SqlSession openSession(Connection connection);
  SqlSession openSession(TransactionIsolationLevel level);

  SqlSession openSession(ExecutorType execType);
  SqlSession openSession(ExecutorType execType, boolean autoCommit);
  SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level);
  SqlSession openSession(ExecutorType execType, Connection connection);

  Configuration getConfiguration();

}

默认实现是DefaultSqlSessionFactory,还有一个是SqlSessonManager(身份不明）

public class DefaultSqlSessionFactory implements SqlSessionFactory {

  private final Configuration configuration;

  public DefaultSqlSessionFactory(Configuration configuration) {
    this.configuration = configuration;
  }
  //此处省去很多openSession(...)
  public Configuration getConfiguration() {
    return configuration;
  }
  //这个才是核心
  private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
      final Environment environment = configuration.getEnvironment();
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      final Executor executor = configuration.newExecutor(tx, execType, autoCommit);
      return new DefaultSqlSession(configuration, executor);
    } 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();
    }
  }

从这个方法中可以看到构建顺序
Configuration --> Environment --> TransactionFactory --> Transaction -> Executor --> DefaultSqlSession