13.4.2Low-level synchronization approach

Classes such asDataSourceUtils(for JDBC),EntityManagerFactoryUtils(for JPA),SessionFactoryUtils(for Hibernate), and so on exist at a lower level. When you want the application code to deal directly with the resource types of the native persistence APIs, you use these classes to ensure that proper Spring Framework-managed instances are obtained, transactions are (optionally) synchronized, and exceptions that occur in the process are properly mapped to a consistent API.

For example, in the case of JDBC, instead of the traditional JDBC approach of calling thegetConnection()method on theDataSource, you instead use Spring’sorg.springframework.jdbc.datasource.DataSourceUtilsclass as follows:

Connection conn = DataSourceUtils.getConnection(dataSource);

If an existing transaction already has a connection synchronized (linked) to it, that instance is returned. Otherwise, the method call triggers the creation of a new connection, which is (optionally) synchronized to any existing transaction, and made available for subsequent reuse in that same transaction. As mentioned, anySQLExceptionis wrapped in a Spring FrameworkCannotGetJdbcConnectionException, one of the Spring Framework’s hierarchy of unchecked DataAccessExceptions. This approach gives you more information than can be obtained easily from theSQLException, and ensures portability across databases, even across different persistence technologies.

This approach also works without Spring transaction management (transaction synchronization is optional), so you can use it whether or not you are using Spring for transaction management.

Of course, once you have used Spring’s JDBC support, JPA support or Hibernate support, you will generally prefer not to useDataSourceUtilsor the other helper classes, because you will be much happier working through the Spring abstraction than directly with the relevant APIs. For example, if you use the SpringJdbcTemplateorjdbc.objectpackage to simplify your use of JDBC, correct connection retrieval occurs behind the scenes and you won’t need to write any special code.