The annotation @Transactional in Spring Boot

Introduce

The @Transactional annotation is part of the Spring Framework and is used to manage transactions declaratively. It can be applied to classes or methods in your service layer.

@Transactional under the hook.

The image depicts that the transactional bound context will applied to all methods in this class. When we call the method annotated by @Transactional by default it will be wrapped within an TransactionAspectSupport class and the actual method is executed in invokeWithinTransaction method (We can use this to check if we are configure transaction in our application correctly).

• In a transaction, a connection is reused across multiple database access object (DAO) method calls. So when we have a limited connection pool and process a business for a long time we can shortly run out of database connection if the business is called frequently.
• Depending on propagation we define in @Transactional the code at line 225 will reuse the existing transaction or create a new one.
• If we mixed use JdbcTemplate and JPA does @Transactional bounded context still apply? The answer is yes. In the below image the update invoke within TransactionAspectSupport

Key to takeaways

• In Spring Data JPA, when we only want to retrieve data without modifying it we should use @Transactional(readOnly=true). Since the JPA doesn't need to keep track state of objects.

Luckily, the spring framework does the job for us to make SimpleJpaRepository (which is the parent class of JpaRepository we usually use) annotated with read-only transactions.

• By default mode of Spring AOP the call directly to a @Transactional annotated methods of the same class will not work.

With this setup, the @Transactional we write is useless since we can't find any TransactionAspectSupport in the call stack.