Tell about locking in JPA. Which ones have you used?

In JPA, there are two main types of locking:

1. Optimistic Locking

   • Used to prevent conflicts during concurrent data updates.
   • Implemented with the @Version annotation in the entity.
   • When updating, the record's version is checked; if it has changed since reading, an OptimisticLockException is thrown.
   • Suitable for systems with low contention for data.

2. Pessimistic Locking

   • Locks at the database level during read or update.
   • Uses methods like EntityManager.lock(entity, LockModeType.PESSIMISTIC_WRITE) or JPQL with LOCK.
   • Ensures that other transactions cannot modify or read the data until the lock is released.
   • Suitable for high-concurrency scenarios where data integrity is crucial.

Example of optimistic locking:

@Entity
public class Product {
    @Id
    private Long id;

    @Version
    private Integer version;

    private String name;
    // getters and setters
}

When updating, JPA checks the version and throws an exception if the data has been modified by another process.

Both locking types are used depending on the consistency and performance requirements.