初始化EntityManager类对象，该怎么办？

Question

I have following abstract dao class with me: I am using find(Long primaryKey) method for getting data. like

public abstract class AbstractDao<T> {
    static final Logger logger = Logger.getLogger(AbstractDao.class);

    @PersistenceContext
    private EntityManager entityManager;

    protected EntityManager getEntityManager() {
        return this.entityManager;
    }

    public T find(Long primaryKey) {
        //Here entityManager is null therefore I am getting null pointer exception
        return entityManager.find(entityClass,primaryKey);
    }
}        

Please suggest some techniques to intitalize entityManager object.

Answer 1

You can remove PersistenceContext annotation from EntityManager and create next abstract method

public abstract void setEntityManager(EntityManager entityManager);

In this way you can put next method in the main class

@PersistenceContext(unitName = "HERE YOU HAVE TO PUT NAME OF ENTITY MANAGER FACTORY")
public void setEntityManager(EntityManager entityManager) {
    this.entityManager = entityManager;
}

and all will be works ;) I have it in my owner DAO and all works