Not allowed to create transaction on shared entitymanager – use spring transactions or ejb cmt instead

Not allowed to create transaction on shared EntityManager

In Java enterprise development, the EntityManager is responsible for managing the persistence of entities in a database. This error message typically occurs when trying to perform a transactional operation on a shared EntityManager without utilizing the appropriate transaction management mechanism.

There are two commonly used transaction management mechanisms in Java enterprise applications:

1. Spring Transactions
2. EJB CMT (Container Managed Transactions)

Let’s discuss each mechanism in detail:

1. Spring Transactions

Spring provides a robust and flexible transaction management framework. To use Spring transactions instead of directly creating transactions on the shared EntityManager, you need to configure your application to use Spring’s transaction management.

Here’s an example of how to use Spring transactions:

        // Define a service class where transactions need to be managed
        public class ProductService {
        
            // Inject the EntityManager
            @PersistenceContext
            private EntityManager entityManager;
        
            // Use Spring's @Transactional annotation to define transaction boundaries
            @Transactional
            public void saveProduct(Product product) {
                // Perform transactional operations
                entityManager.persist(product);
            }
        }
    

The above example demonstrates how to use Spring’s @Transactional annotation to indicate that the saveProduct() method should be executed within a transaction. The EntityManager is injected using the @PersistenceContext annotation.

2. EJB CMT (Container Managed Transactions)

EJB CMT provides another built-in transaction management mechanism in Java EE applications. Similar to Spring transactions, EJB CMT allows you to delegate transaction management to the container.

Here’s an example of how to use EJB CMT:

        // Define an EJB bean where transactions need to be managed
        @Stateless
        public class ProductService {
        
            // Inject the EntityManager
            @PersistenceContext
            private EntityManager entityManager;
        
            // Use EJB's @TransactionAttribute annotation to define transaction boundaries
            @TransactionAttribute(TransactionAttributeType.REQUIRED)
            public void saveProduct(Product product) {
                // Perform transactional operations
                entityManager.persist(product);
            }
        }
    

The example above demonstrates how to use EJB’s @TransactionAttribute annotation to indicate that the saveProduct() method should be executed within a required transaction. The EntityManager is injected using the @PersistenceContext annotation.

Both Spring transactions and EJB CMT provide similar functionalities and allow you to manage transactions effectively in Java enterprise applications. Choose the one that best fits your project requirements and existing framework.