Spring Transactions

Question 1

On which layer should transaction be applied? Dao or data layer vs serivce or business logic layer?

Answer 1

Transactions should be applied on Service layer or Business logic layer.

Question 2

Which annotation is used for specifying transactional?

Answer 2

@Transactional

Question 3

How are transactions managed in spring technically?

Answer 3

ThreadLocal and AOP are used together to manage transactions in Spring.

Question 4

If you have two databases is it possible to have two different transaction managers and provide detail in annotation as to which should be injected in Bean or Repository?

Answer 4

Yes it is possible to do that.
First we need to define two transaction managers with different qualifiers.

bean id=”tm1” class=”…JpaTransactionmanager”
property name=”entityManagerFactory” ref=”entityManagerFactory1”
qualifier value=”account”

bean id=”transactionManager2” class=”…JpaTransactionManager”
property name=”entityManagerFactory” ref=”entityManagerFactory2”
qualifier value=”businessData”

Then this qualifier can be used in annotation to specify which transaction manager should be used.

public class TransactionalService {

@Transactional("account")
public void doSomethingToAccount() {}

@Transactional(“businessData”)
public void doSomethingInBusinessData() {…}

}

Question 5

Transaction management can be done in how many ways with Spring?

Answer 5

In two ways, declarative transaction management which is high level one, using annotation. Or Programmatic transaction management, which is more advanced and flexible.

Question 6

By default Spring transaction management is single threaded or multi-threaded?

Answer 6

Spring transactions work well with single thread, as they heavily use ThreadLocal for handling transactions. Problem arises when need to manage transactions across multiple threads.

Question 7

How does spring declarative transaction management work?

Answer 7

It uses AOP proxies and the transactional advice is driven by metadata. The combination of AOP with transactional metadata yields an AOP proxy that uses a TransactionInterceptor in conjunction with an appropriate PlatformTransactionManager implementation to drive transactions around method invocations.

Question 8

Flow of declarative transaction management

Answer 8

Caller => AOP Proxy => Transaction Advisor (transaction created on way in and committed or rolled back on way out) => Custom Advisor (Custom interceptors may run before or after the transaction advisor) => Target method (Business logic) => Custom Advisor => Transaction Advisor => AOP Proxy => Caller