Synchronizing resources with transactions - Java-Springs

It should now be clear how you create different transaction managers, and how they are linked to related resources that need to be synchronized to transactions (for example Data Source Transaction Manager to a JDBC Data Source,Hibernate Transaction Manager to a Hibernate Session Factory, and so forth). This how the application code, directly or indirectly using a persistence API such as JDBC, Hibernate, or JDO, ensures that these resources are created, reused, and cleaned up properly.

High-level synchronization approach

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.

Low-level synchronization approach

Classes such as DataSourceUtils (for JDBC), Entity Manager FactoryUtils (for JPA), Session FactoryUtils (for Hibernate), Persistence Manager FactoryUtils (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 Frame work-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 th get Connection() method on the DataSource, you instead use Spring'sorg. spring frame work. jdbc. data source. Data Source Utils class as follows: Connection conn = Data Source Utils. get Connection( data Source);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.

Transaction Aware Data Source Proxy

At the very lowest level exists the Transaction Aware Data Source Proxy 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 Data Source 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.

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