Transactions with Spring and JPA

1. Overview

This tutorial will discuss the right way to configure Spring Transactions, how to use the @Transactional annotation and common pitfalls.

For a more in-depth discussion on the core persistence configuration, check out the Spring with JPA tutorial.

Basically, there are two distinct ways to configure Transactions, annotations and AOP, each with its own advantages. We’re going to discuss the more common annotation config here.

2. Configure Transactions

Spring 3.1 introduces the @EnableTransactionManagement annotation that we can use in a @Configuration class to enable transactional support:

@Configuration
@EnableTransactionManagement
public class PersistenceJPAConfig{

   @Bean
   public LocalContainerEntityManagerFactoryBean entityManagerFactory() {
       //...
   }

   @Bean
   public PlatformTransactionManager transactionManager() {
      JpaTransactionManager transactionManager = new JpaTransactionManager();
      transactionManager.setEntityManagerFactory(entityManagerFactory().getObject());
      return transactionManager;
   }
}

However, if we’re using a Spring Boot project and have a spring-data-* or spring-tx dependencies on the classpath, then transaction management will be enabled by default.

3. Configure Transactions With XML

For versions before 3.1, or if Java is not an option, here is the XML configuration using annotation-driven and namespace support:

<bean id="txManager" class="org.springframework.orm.jpa.JpaTransactionManager">
   <property name="entityManagerFactory" ref="myEmf" />
</bean>
<tx:annotation-driven transaction-manager="txManager" />

4. The @Transactional Annotation

With transactions configured, we can now annotate a bean with @Transactional either at the class or method level:

@Service
@Transactional
public class FooService {
    //...
}

The annotation supports further configuration as well:

• the Propagation Type of the transaction
• the Isolation Level of the transaction
• a Timeout for the operation wrapped by the transaction
• a readOnly flag – a hint for the persistence provider that the transaction should be read only
• the Rollback rules for the transaction

Note that by default, rollback happens for runtime, unchecked exceptions only. The checked exception does not trigger a rollback of the transaction. We can, of course, configure this behavior with the rollbackFor and noRollbackFor annotation parameters.

5. Potential Pitfalls

5.1. Transactions and Proxies

At a high level, Spring creates proxies for all the classes annotated with @Transactional, either on the class or on any of the methods. The proxy allows the framework to inject transactional logic before and after the running method, mainly for starting and committing the transaction.

What’s important to keep in mind is that, if the transactional bean is implementing an interface, by default the proxy will be a Java Dynamic Proxy. This means that only external method calls that come in through the proxy will be intercepted. Any self-invocation calls will not start any transaction, even if the method has the @Transactional annotation.

Another caveat of using proxies is that only public methods should be annotated with @Transactional. Methods of any other visibilities will simply ignore the annotation silently as these are not proxied.

5.2. Changing the Isolation Level

courseDao.createWithRuntimeException(course);

We can also change the transaction isolation level:

@Transactional(isolation = Isolation.SERIALIZABLE)

Note that this has actually been introduced in Spring 4.1; if we run the above example before Spring 4.1, it will result in:

org.springframework.transaction.InvalidIsolationLevelException: Standard JPA does not support custom isolation levels – use a special JpaDialect for your JPA implementation

5.3. Read-Only Transactions

The readOnly flag usually generates confusion, especially when working with JPA. From the Javadoc:

This just serves as a hint for the actual transaction subsystem; it will not necessarily cause failure of write access attempts. A transaction manager which cannot interpret the read-only hint will not throw an exception when asked for a read-only transaction.

The fact is that we can’t be sure that an insert or update won’t occur when the readOnly flag is set. This behavior is vendor-dependent, whereas JPA is vendor agnostic.

It’s also important to understand that the readOnly flag is only relevant inside a transaction. If an operation occurs outside of a transactional context, the flag is simply ignored. A simple example of that would call a method annotated with:

@Transactional(propagation = Propagation.SUPPORTS, readOnly = true)

From a non-transactional context, a transaction will not be created and the readOnly flag will be ignored.

5.4. Transaction Logging

A helpful method to understand transactional-related issues is fine-tuning logging in the transactional packages. The relevant package in Spring is “org.springframework.transaction”, which should be configured with a logging level of TRACE.

5.5. Transaction Rollback

The @Transactional annotation is the metadata that specifies the semantics of the transactions on a method. We have two ways to rollback a transaction: declarative and programmatic.

In the declarative approach, we annotate the methods with the @Transactional annotation. The @Transactional annotation makes use of the attributes rollbackFor or rollbackForClassName to rollback the transactions, and the attributes noRollbackFor or noRollbackForClassName to avoid rollback on listed exceptions.

The default rollback behavior in the declarative approach will rollback on runtime exceptions.

Let’s see a simple example using the declarative approach to rollback a transaction for runtime exceptions or errors:

@Transactional
public void createCourseDeclarativeWithRuntimeException(Course course) {
    courseDao.create(course);
    throw new DataIntegrityViolationException("Throwing exception for demoing Rollback!!!");
}

Next, we’ll use the declarative approach to rollback a transaction for the listed checked exceptions. The rollback in our example is on SQLException:

@Transactional(rollbackFor = { SQLException.class })
public void createCourseDeclarativeWithCheckedException(Course course) throws SQLException {
    courseDao.create(course);
    throw new SQLException("Throwing exception for demoing rollback");
}

Let’s see a simple use of attribute noRollbackFor in the declarative approach to prevent rollback of the transaction for the listed exception:

@Transactional(noRollbackFor = { SQLException.class })
public void createCourseDeclarativeWithNoRollBack(Course course) throws SQLException {
    courseDao.create(course);
    throw new SQLException("Throwing exception for demoing rollback");
}

In the programmatic approach, we rollback the transactions using TransactionAspectSupport:

public void createCourseDefaultRatingProgramatic(Course course) {
    try {
       courseDao.create(course);
    } catch (Exception e) {
       TransactionAspectSupport.currentTransactionStatus().setRollbackOnly();
    }
}

6. Conclusion

In this article, we covered the basic configuration of transactional semantics using both Java and XML. We also learned how to use @Transactional, and the best practices of a Transactional Strategy.