CODEWITHSUNDEEP
javajpaejbejb-3.1
Alstresh
Alstresh

Reputation: 583

singleton ejb with PersistenceContext and LockType.READ

@Singleton EJBs like this:

  @Singleton
  public class MySingleton {
     @PersistenceContext
     private EntityManager em;
     ...

     @Lock(LockType.READ)
     public void doPersistanceAction() {
     }

  }

So all callers of MySingleton#doPersistanceAction() would use the same instance of EntityManager simultaneously. And persistence context with attached entitys will share between callers. And transaction started by one caller may be commited by another. Whether the ejb container handle such a situation?

Upvotes: 1

Views: 1296

Answers (1)

Nayan Wadekar
Nayan Wadekar

Reputation: 11612

So all callers of MySingleton#doPersistanceAction() would use the same instance of EntityManager simultaneously

Yes, but it isn't a preferred & isn't thread-safe. Instead you should inject EntityManagerFactory & then within method you can get EntityManager from it.

And persistence context with attached entitys will share between callers

Yes, same EntityManager instance is shared.

And transaction started by one caller may be commited by another

LockType.READ : For read-only operations. Allows simultaneous access to methods designated as READ, as long as no WRITE lock is held.

Therefore, as you have read-only operation, it shouldn't matter, but you need to revisit design.

Whether the ejb container handle such a situation?

Container will be responsible for initialization, injection, concurrency etc. for singleton bean, but you have to utilize it correctly.

Upvotes: 1

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