M03 Q10 How are you going to define a transaction in Spring? What does @Transactional do? What is the PlatformTransactionManager?

To use transactions in Spring Framework, you need to:

1. Enable transaction management by using @EnableTransactionManagement annotation on top of your Configuration class.
2. Create bean method in configuration class that will return bean implementing interface PlatformTransactionManager, examples of transactions managers (DataSourceTransactionManager, JtaTransactionManager, JpaTransactionManager)
3. Use @Transactional annotation on top of classes or methods that should involve transaction management

@Transactional annotation can be used on top of classes or methods to enable transaction management for entire class or specified methods. When method with @Transactional annotation is called, invocation is proxied by TransactionInterceptor and TransactionAspectSupport which are using PlatformTransactionManager to manage transaction.

Transaction is being started at the beginning of the method (if none transaction exists), and it is being committed at the end of successful execution. Transaction can be rolled back upon exception being thrown. This behavior is dependent on transaction propagation type.

@Transactional annotation allows you to configure following attributes:

• Transaction Manager
• Propagation Type
• Isolation Level
• Timeout for Transaction
• Read Only Flag
• Define which exception types will cause transaction rollback
• Define which exception types will not cause transaction rollback

PlatformTransactionManager is an interface that is used by declarative Spring’s AOP Transaction Management to create, commit and rollback transactions.

PlatformTransactionManager contains following methods:

• getTransaction – returns currently active transaction or creates new one
• commit – commits transaction, or rolls back transaction if it was marked for rollback
• rollback – performs rollback of transaction