I would like to know what I need to do in order to make the access to DB thread-safe.
This is my Entity class:
@Entity
@Table(name = "students")
@NamedQuery(name = "Student.getAll", query = "SELECT s FROM Student s")
public class Student {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@Column(length = 32, name = "name")
private String name;
// ... constructor, getters and setters, toString ...
}
This is the DbService class:
public class DbService {
public EntityManager em = Persistence
.createEntityManagerFactory("MyPersistenceUnit")
.createEntityManager();
public Student add(Student student) {
EntityTransaction tx = em.getTransaction();
tx.begin();
Student studentFromDb = em.merge(student);
tx.commit();
return studentFromDb;
}
public void delete(long id) {
EntityTransaction tx = em.getTransaction();
tx.begin();
em.remove(get(id));
tx.commit();
}
public Student get(long id) {
return em.find(Student.class, id);
}
public void update(Student student) {
EntityTransaction tx = em.getTransaction();
tx.begin();
em.merge(student);
tx.commit();
}
public List<Student> getAll() {
TypedQuery<Student> namedQuery =
em.createNamedQuery("Student.getAll", Student.class);
return namedQuery.getResultList();
}
}
And here is a class that work with DbService:
public class SomeDbWorker implements Runnable {
@Override
public void run() {
DbService service = new DbService();
// do something ...
service.add( ... );
service.delete( ... );
service.getAll();
// ...
}
}
- Is it enough making add(), delete(), update() and getAll() methods synchronized?
- Can I create multiple instances of DbService like in my source? Or do I need to create only one instance?
- Maybe I should to use the singleton design pattern? Or make DbService static with all methods?
