TransactionFactory是产生Transaction的工厂

接口如下：

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

  /**
   * Sets transaction factory custom properties.
   * @param props
   */
  void setProperties(Properties props);

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

}

每种Transaction都有一个对应的工厂。
分别是JdbcTransactionFactory, ManagedTransactionFactory和SpringManagedTransactionFactory
实现都极其简单，直接new相应的产品即可

public class JdbcTransactionFactory implements TransactionFactory {

  public void setProperties(Properties props) {
  }

  public Transaction newTransaction(Connection conn) {
    return new JdbcTransaction(conn);
  }

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

xx