The preferred approach is to use Spring's highest level template based persistence integration APIs or to use native ORM APIs with transaction- aware factory beans or proxies for managing the native resource factories. These transaction-aware solutions internally handle resource creation and reuse, cleanup, optional transaction synchronization of the resources, and exception mapping. Thus user data access code does not have to address these tasks, but can be focused purely on non-boilerplate persistence logic. Generally, you use the native ORM API or take a template approach for JDBC access by using the JdbcTemplate. These solutions are detailed in subsequent chapters of this reference documentation.

Classes such as DataSourceUtils (for JDBC), EntityManagerFactoryUtils (for JPA), SessionFactoryUtils (for Hibernate), PersistenceManagerFactoryUtils (for JDO), 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 the getConnection() method on the DataSource, you instead use Spring's org.springframework.jdbc.datasource.DataSourceUtils class 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, any SQLException is wrapped in a Spring Framework CannotGetJdbcConnectionException, one of the Spring Framework's hierarchy of unchecked DataAccessExceptions. This approach gives you more information than can be obtained easily from the SQLException, 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 use DataSourceUtils or 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 Spring JdbcTemplate or jdbc.object package to simplify your use of JDBC, correct connection retrieval occurs behind the scenes and you won't need to write any special code.

At the very lowest level exists the TransactionAwareDataSourceProxy class. This is a proxy for a target DataSource, which wraps the target DataSource to add awareness of Spring-managed transactions. In this respect, it is similar to a transactional JNDI DataSource as provided by a Java EE server.

It should almost never be necessary or desirable to use this class, except when existing code must be called and passed a standard JDBC DataSource interface implementation. In that case, it is possible that this code is usable, but participating in Spring managed transactions. It is preferable to write your new code by using the higher level abstractions mentioned above.