Introducción a las transacciones en Java y Spring

Programación

1. Introducción

En este tutorial, entenderemos qué se entiende por transacciones en Java. De ese modo, entenderemos cómo realizar transacciones locales de recursos y transacciones globales. Esto también nos permitirá explorar diferentes formas de administrar transacciones en Java y Spring.

2. ¿Qué es una transacción?

Las transacciones en Java, como en general, se refieren a una serie de acciones que deben completarse con éxito. Por lo tanto, si una o más acciones fallan, todas las demás deben retroceder dejando el estado de la aplicación sin cambios . Esto es necesario para garantizar que la integridad del estado de la aplicación nunca se vea comprometida.

Además, estas transacciones pueden involucrar uno o más recursos como base de datos, cola de mensajes, dando lugar a diferentes formas de realizar acciones bajo una transacción. Estos incluyen la realización de transacciones de recursos locales con recursos individuales. Alternativamente, varios recursos pueden participar en una transacción global.

3. Transacciones locales de recursos

Primero exploraremos cómo podemos usar transacciones en Java mientras trabajamos con recursos individuales. Aquí, podemos tener varias acciones individuales que realizamos con un recurso como una base de datos . Pero, podemos querer que sucedan como un todo unificado, como en una unidad de trabajo indivisible. En otras palabras, queremos que estas acciones se realicen en una sola transacción.

En Java, tenemos varias formas de acceder y operar en un recurso como una base de datos. Por lo tanto, la forma en que manejamos las transacciones tampoco es la misma. En esta sección, encontraremos cómo podemos usar transacciones con algunas de estas bibliotecas en Java que se usan con bastante frecuencia.

3.1. JDBC

Java Database Connectivity (JDBC) es la API en Java que define cómo acceder a las bases de datos en Java . Los diferentes proveedores de bases de datos proporcionan controladores JDBC para conectarse a la base de datos de manera independiente del proveedor. Entonces, recuperamos una conexión de un controlador para realizar diferentes operaciones en la base de datos:

JDBC nos brinda las opciones para ejecutar declaraciones en una transacción. El comportamiento predeterminado de una conexión es la confirmación automática . Para aclarar, lo que esto significa es que cada declaración se trata como una transacción y se confirma automáticamente inmediatamente después de la ejecución.

Sin embargo, si deseamos agrupar varias declaraciones en una sola transacción, esto también es posible:

Connection connection = DriverManager.getConnection(CONNECTION_URL, USER, PASSWORD); try { connection.setAutoCommit(false); PreparedStatement firstStatement = connection .prepareStatement("firstQuery"); firstStatement.executeUpdate(); PreparedStatement secondStatement = connection .prepareStatement("secondQuery"); secondStatement.executeUpdate(); connection.commit(); } catch (Exception e) { connection.rollback(); }

Aquí, hemos desactivado el modo de confirmación automática de Connection . Por lo tanto, podemos definir manualmente el límite de la transacción y realizar una confirmación o una reversión . JDBC también nos permite establecer un punto de guardado que nos brinda más control sobre cuánto revertir.

3.2. JPA

La API de persistencia de Java (JPA) es una especificación en Java que se puede utilizar para cerrar la brecha entre los modelos de dominio orientados a objetos y los sistemas de bases de datos relacionales . Por lo tanto, existen varias implementaciones de JPA disponibles de terceros como Hibernate, EclipseLink e iBatis.

En JPA, podemos definir clases regulares como una entidad que les proporciona una identidad persistente. La clase EntityManager proporciona la interfaz necesaria para trabajar con múltiples entidades dentro de un contexto de persistencia . El contexto de persistencia se puede considerar como una caché de primer nivel donde se administran las entidades:

El contexto de persistencia aquí puede ser de dos tipos, de ámbito de transacción o de ámbito extendido. Un contexto de persistencia con alcance de transacción está vinculado a una sola transacción. Mientras que el contexto de persistencia de alcance extendido puede abarcar varias transacciones. El alcance predeterminado de un contexto de persistencia es el alcance de la transacción .

Veamos cómo podemos crear un EntityManager y definir un límite de transacción manualmente:

EntityManagerFactory entityManagerFactory = Persistence.createEntityManagerFactory("jpa-example"); EntityManager entityManager = entityManagerFactory.createEntityManager(); try { entityManager.getTransaction().begin(); entityManager.persist(firstEntity); entityManager.persist(secondEntity); entityManager.getTransaction().commit(); } catch (Exceotion e) { entityManager.getTransaction().rollback(); }

Aquí, estamos creando un EntityManager desde EntityManagerFactory dentro del contexto de un contexto de persistencia con alcance de transacción. Luego, estamos definiendo el límite de la transacción con los métodos begin , commit y rollback .

3.3. JMS

Java Messaging Service (JMS) es una especificación en Java que permite que las aplicaciones se comuniquen de forma asíncrona mediante mensajes . La API nos permite crear, enviar, recibir y leer mensajes de una cola o tema. Hay varios servicios de mensajería que cumplen con las especificaciones de JMS, incluidos OpenMQ y ActiveMQ.

La API de JMS admite la agrupación de varias operaciones de envío o recepción en una única transacción. Sin embargo, por la naturaleza de la arquitectura de integración basada en mensajes, la producción y el consumo de un mensaje no pueden formar parte de la misma transacción . El alcance de la transacción permanece entre el cliente y el proveedor JMS:

JMS nos permite crear una sesión a partir de una conexión que obtenemos de un ConnectionFactory específico del proveedor . Tenemos la opción de crear una sesión que se transmita o no . Para no transacciones Sesión s , podemos definir, además, un modo apropiado reconocer también.

Veamos cómo podemos crear una sesión con transacción para enviar varios mensajes en una transacción:

ActiveMQConnectionFactory connectionFactory = new ActiveMQConnectionFactory(CONNECTION_URL); Connection connection = = connectionFactory.createConnection(); connection.start(); try { Session session = connection.createSession(true, 0); Destination = destination = session.createTopic("TEST.FOO"); MessageProducer producer = session.createProducer(destination); producer.send(firstMessage); producer.send(secondMessage); session.commit(); } catch (Exception e) { session.rollback(); }

Aquí, estamos creando un MessageProducer para el destino del tipo de tema. Obtenemos el destino de la sesión que creamos anteriormente. Además, usamos Session para definir los límites de las transacciones utilizando los métodos commit y rollback .

4. Transacciones globales

Como vimos, las transacciones locales de recursos nos permiten realizar múltiples operaciones dentro de un solo recurso como un todo unificado. Pero, con bastante frecuencia, nos ocupamos de operaciones que abarcan varios recursos . Por ejemplo, operación en dos bases de datos diferentes o una base de datos y una cola de mensajes. Aquí, el soporte de transacciones locales dentro de los recursos no será suficiente para nosotros.

Lo que necesitamos en estos escenarios es un mecanismo global para demarcar transacciones que abarcan múltiples recursos participantes . Esto a menudo se conoce como transacciones distribuidas y hay especificaciones que se han propuesto para tratarlas de manera efectiva.

La Especificación XA es una de esas especificaciones que define a un administrador de transacciones para controlar las transacciones en múltiples recursos . Java tiene un soporte bastante maduro para transacciones distribuidas que cumplen con la Especificación XA a través de los componentes JTA y JTS.

4.1. JTA

Java Transaction API (JTA) is a Java Enterprise Edition API developed under the Java Community Process. It enables Java applications and application servers to perform distributed transactions across XA resources. JTA is modeled around XA architecture, leveraging two-phase commit.

JTA specifies standard Java interfaces between a transaction manager and the other parties in a distributed transaction:

Let's understand some of the key interfaces highlighted above:

  • TransactionManager: An interface which allows an application server to demarcate and control transactions
  • UserTransaction: This interface allows an application program to demarcate and control transactions explicitly
  • XAResource: The purpose of this interface is to allow a transaction manager to work with resource managers for XA-compliant resources

4.2. JTS

Java Transaction Service (JTS) is a specification for building the transaction manager that maps to the OMG OTS specification. JTS uses the standard CORBA ORB/TS interfaces and Internet Inter-ORB Protocol (IIOP) for transaction context propagation between JTS transaction managers.

At a high level, it supports the Java Transaction API (JTA). A JTS transaction manager provides transaction services to the parties involved in a distributed transaction:

Services that JTS provides to an application are largely transparent and hence we may not even notice them in the application architecture. JTS is architected around an application server which abstracts all transaction semantics from the application programs.

5. JTA Transaction Management

Now it's time to understand how we can manage a distributed transaction using JTA. Distributed transactions are not trivial solutions and hence have cost implications as well. Moreover, there are multiple options that we can choose from to include JTA in our application. Hence, our choice must be in the view of overall application architecture and aspirations.

5.1. JTA in Application Server

As we have seen earlier, JTA architecture relies on the application server to facilitate a number of transaction-related operations. One of the key services it relies on the server to provide is a naming service through JNDI. This is where XA resources like data sources are bound to and retrieved from.

Apart from this, we have a choice in terms of how we want to manage the transaction boundary in our application. This gives rise to two types of transactions within the Java application server:

  • Container-managed Transaction: As the name suggests, here the transaction boundary is set by the application server. This simplifies the development of Enterprise Java Beans (EJB) as it does not include statements related to transaction demarcation and relies solely on the container to do so. However, this does not provide enough flexibility for the application.
  • Bean-managed Transaction: Contrary to the container-managed transaction, in a bean-managed transaction EJBs contain the explicit statements to define the transaction demarcation. This provides precise control to the application in marking the boundaries of the transaction, albeit at the cost of more complexity.

One of the main drawbacks of performing transactions in the context of an application server is that the application becomes tightly coupled with the server. This has implications with respect to testability, manageability, and portability of the application. This is more profound in microservice architecture where the emphasis is more on developing server-neutral applications.

5.2. JTA Standalone

The problems we discussed in the last section have provided a huge momentum towards creating solutions for distributed transactions that does not rely on an application server. There are several options available to us in this regard, like using transaction support with Spring or use a transaction manager like Atomikos.

Let's see how we can use a transaction manager like Atomikos to facilitate a distributed transaction with a database and a message queue. One of the key aspects of a distributed transaction is enlisting and delisting the participating resources with the transaction monitor. Atomikos takes care of this for us. All we have to do is use Atomikos-provided abstractions:

AtomikosDataSourceBean atomikosDataSourceBean = new AtomikosDataSourceBean(); atomikosDataSourceBean.setXaDataSourceClassName("com.mysql.cj.jdbc.MysqlXADataSource"); DataSource dataSource = atomikosDataSourceBean;

Here, we are creating an instance of AtomikosDataSourceBean and registering the vendor-specific XADataSource. From here on, we can continue using this like any other DataSource and get the benefits of distributed transactions.

Similarly, we have an abstraction for message queue which takes care of registering the vendor-specific XA resource with the transaction monitor automatically:

AtomikosConnectionFactoryBean atomikosConnectionFactoryBean = new AtomikosConnectionFactoryBean(); atomikosConnectionFactoryBean.setXaConnectionFactory(new ActiveMQXAConnectionFactory()); ConnectionFactory connectionFactory = atomikosConnectionFactoryBean;

Here, we are creating an instance of AtomikosConnectionFactoryBean and registering the XAConnectionFactory from an XA-enabled JMS vendor. After this, we can continue to use this as a regular ConnectionFactory.

Now, Atomikos provides us the last piece of the puzzle to bring everything together, an instance of UserTransaction:

UserTransaction userTransaction = new UserTransactionImp();

Now, we are ready to create an application with distributed transaction spanning across our database and the message queue:

try { userTransaction.begin(); java.sql.Connection dbConnection = dataSource.getConnection(); PreparedStatement preparedStatement = dbConnection.prepareStatement(SQL_INSERT); preparedStatement.executeUpdate(); javax.jms.Connection mbConnection = connectionFactory.createConnection(); Session session = mbConnection.createSession(true, 0); Destination destination = session.createTopic("TEST.FOO"); MessageProducer producer = session.createProducer(destination); producer.send(MESSAGE); userTransaction.commit(); } catch (Exception e) { userTransaction.rollback(); }

Here, we are using the methods begin and commit in the class UserTransaction to demarcate the transaction boundary. This includes saving a record in the database as well as publishing a message to the message queue.

6. Transactions Support in Spring

We have seen that handling transactions are rather an involved task which includes a lot of boilerplate coding and configurations. Moreover, each resource has its own way of handling local transactions. In Java, JTA abstracts us from these variations but further brings provider-specific details and the complexity of the application server.

Spring platform provides us a much cleaner way of handling transactions, both resource local and global transactions in Java. This together with the other benefits of Spring creates a compelling case for using Spring to handle transactions. Moreover, it's quite easy to configure and switch a transaction manager with Spring, which can be server provided or standalone.

Spring provides us this seamless abstraction by creating a proxy for the methods with transactional code. The proxy manages the transaction state on behalf of the code with the help of TransactionManager:

The central interface here is PlatformTransactionManager which has a number of different implementations available. It provides abstractions over JDBC (DataSource), JMS, JPA, JTA, and many other resources.

6.1. Configurations

Let's see how we can configure Spring to use Atomikos as a transaction manager and provide transactional support for JPA and JMS. We'll begin by defining a PlatformTransactionManager of the type JTA:

@Bean public PlatformTransactionManager platformTransactionManager() throws Throwable { return new JtaTransactionManager( userTransaction(), transactionManager()); }

Here, we are providing instances of UserTransaction and TransactionManager to JTATransactionManager. These instances are provided by a transaction manager library like Atomikos:

@Bean public UserTransaction userTransaction() { return new UserTransactionImp(); } @Bean(initMethod = "init", destroyMethod = "close") public TransactionManager transactionManager() { return new UserTransactionManager(); }

The classes UserTransactionImp and UserTransactionManager are provided by Atomikos here.

Further, we need to define the JmsTemplete which the core class allowing synchronous JMS access in Spring:

@Bean public JmsTemplate jmsTemplate() throws Throwable { return new JmsTemplate(connectionFactory()); }

Here, ConnectionFactory is provided by Atomikos where it enables distributed transaction for Connection provided by it:

@Bean(initMethod = "init", destroyMethod = "close") public ConnectionFactory connectionFactory() { ActiveMQXAConnectionFactory activeMQXAConnectionFactory = new ActiveMQXAConnectionFactory(); activeMQXAConnectionFactory.setBrokerURL("tcp://localhost:61616"); AtomikosConnectionFactoryBean atomikosConnectionFactoryBean = new AtomikosConnectionFactoryBean(); atomikosConnectionFactoryBean.setUniqueResourceName("xamq"); atomikosConnectionFactoryBean.setLocalTransactionMode(false); atomikosConnectionFactoryBean.setXaConnectionFactory(activeMQXAConnectionFactory); return atomikosConnectionFactoryBean; }

So, as we can see, here we are wrapping a JMS provider-specific XAConnectionFactory with AtomikosConnectionFactoryBean.

Next, we need to define an AbstractEntityManagerFactoryBean that is responsible for creating JPA EntityManagerFactory bean in Spring:

@Bean public LocalContainerEntityManagerFactoryBean entityManager() throws SQLException { LocalContainerEntityManagerFactoryBean entityManager = new LocalContainerEntityManagerFactoryBean(); entityManager.setDataSource(dataSource()); Properties properties = new Properties(); properties.setProperty( "javax.persistence.transactionType", "jta"); entityManager.setJpaProperties(properties); return entityManager; }

As before, the DataSource that we set in the LocalContainerEntityManagerFactoryBean here is provided by Atomikos with distributed transactions enabled:

@Bean(initMethod = "init", destroyMethod = "close") public DataSource dataSource() throws SQLException { MysqlXADataSource mysqlXaDataSource = new MysqlXADataSource(); mysqlXaDataSource.setUrl("jdbc:mysql://127.0.0.1:3306/test"); AtomikosDataSourceBean xaDataSource = new AtomikosDataSourceBean(); xaDataSource.setXaDataSource(mysqlXaDataSource); xaDataSource.setUniqueResourceName("xads"); return xaDataSource; }

Here again, we are wrapping the provider-specific XADataSource in AtomikosDataSourceBean.

6.2. Transaction Management

Having gone through all the configurations in the last section, we must feel quite overwhelmed! We may even question the benefits of using Spring after all. But do remember that all this configuration has enabled us abstraction from most of the provider-specific boilerplate and our actual application code does not need to be aware of that at all.

So, now we are ready to explore how to use transactions in Spring where we intend to update the database and publish messages. Spring provides us two ways to achieve this with their own benefits to choose from. Let's understand how we can make use of them:

  • Declarative Support

The easiest way to use transactions in Spring is with declarative support. Here, we have a convenience annotation available to be applied at the method or even at the class. This simply enables global transaction for our code:

@PersistenceContext EntityManager entityManager; @Autowired JmsTemplate jmsTemplate; @Transactional(propagation = Propagation.REQUIRED) public void process(ENTITY, MESSAGE) { entityManager.persist(ENTITY); jmsTemplate.convertAndSend(DESTINATION, MESSAGE); }

The simple code above is sufficient to allow a save-operation in the database and a publish-operation in message queue within a JTA transaction.

  • Programmatic Support

While the declarative support is quite elegant and simple, it does not offer us the benefit of controlling the transaction boundary more precisely. Hence, if we do have a certain need to achieve that, Spring offers programmatic support to demarcate transaction boundary:

@Autowired private PlatformTransactionManager transactionManager; public void process(ENTITY, MESSAGE) { TransactionTemplate transactionTemplate = new TransactionTemplate(transactionManager); transactionTemplate.executeWithoutResult(status -> { entityManager.persist(ENTITY); jmsTemplate.convertAndSend(DESTINATION, MESSAGE); }); }

So, as we can see, we have to create a TransactionTemplate with the available PlatformTransactionManager. Then we can use the TransactionTemplete to process a bunch of statements within a global transaction.

7. Afterthoughts

As we have seen that handling transactions, particularly those that span across multiple resources are complex. Moreover, transactions are inherently blocking which is detrimental to latency and throughput of an application. Further, testing and maintaining code with distributed transactions is not easy, especially if the transaction depends on the underlying application server. So, all in all, it's best to avoid transactions at all if we can!

But that is far from reality. In short, in real-world applications, we do often have a legitimate need for transactions. Although it's possible to rethink the application architecture without transactions, it may not always be possible. Hence, we must adopt certain best practices when working with transactions in Java to make our applications better:

  • One of the fundamental shifts we should adopt is to use standalone transaction managers instead of those provided by an application server. This alone can simplify our application greatly. Moreover, it's much suited for cloud-native microservice architecture.
  • Further, an abstraction layer like Spring can help us contain the direct impact of providers like JPA or JTA providers. So, this can enable us to switch between providers without much impact on our business logic. Moreover, it takes away the low-level responsibilities of managing the transaction state from us.
  • Lastly, we should be careful in picking the transaction boundary in our code. Since transactions are blocking, it's always better to keep the transaction boundary as restricted as possible. If necessary we should prefer programmatic over declarative control for transactions.

8. Conclusion

En resumen, en este tutorial discutimos las transacciones en el contexto de Java. Pasamos por el soporte para transacciones locales de recursos individuales en Java para diferentes recursos. También analizamos las formas de lograr transacciones globales en Java.

Además, analizamos diferentes formas de administrar transacciones globales en Java. Además, entendimos cómo Spring nos facilita el uso de transacciones en Java.

Finalmente, analizamos algunas de las mejores prácticas al trabajar con transacciones en Java.