java - Some clarification about Spring @Transactional annotation on a method

Question

I am quite new in Spring world and I have developed a simple project that use Spring 3.2.1 and Hibernate 4.1.9 to implement a DAO. The project work correctly but I have some doubts about the use of @Transactional Spring annotation on CRUD method of this DAO.

This is the entire code of the class that implement the CRUD operation of my project:

package org.andrea.myexample.HibernateOnSpring.dao;

import java.util.List;

import org.andrea.myexample.HibernateOnSpring.entity.Person;

import org.hibernate.Criteria;
import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.SessionFactory;
import org.hibernate.cfg.Configuration;
import org.hibernate.service.ServiceRegistry;
import org.hibernate.service.ServiceRegistryBuilder;
import org.springframework.transaction.annotation.Transactional;

public class PersonDAOImpl implements PersonDAO {

    // Factory per la creazione delle sessioni di Hibernate:
    private static SessionFactory sessionFactory;

    // Metodo Setter per l'iniezione della dipendenza della SessionFactory:
    public void setSessionFactory(SessionFactory sessionFactory) {
        this.sessionFactory = sessionFactory;
    }

    /** CREATE CRUD Operation:
     * Aggiunge un nuovo record rappresentato nella tabella rappresentato
     * da un oggetto Person
     */
    @Transactional(readOnly = false)
    public Integer addPerson(Person p) {

        System.out.println("Inside addPerson()");

        Session session = sessionFactory.openSession();

        Transaction tx = null;
        Integer personID = null;

        try {
            tx = session.beginTransaction();

            personID = (Integer) session.save(p);
            tx.commit();
        } catch (HibernateException e) {
            if (tx != null)
                tx.rollback();
            e.printStackTrace();
        } finally {
            session.close();
        }

        return personID;

    }

    // READ CRUD Operation (legge un singolo record avente uno specifico id):
    public Person getById(int id) {

        System.out.println("Inside getById()");

        Session session = sessionFactory.openSession();

        Transaction tx = null;          
        Person retrievedPerson = null;  

        try {
            tx = session.beginTransaction();
            retrievedPerson = (Person) session.get(Person.class, id);
            tx.commit();
        }catch (HibernateException e) { 
            if (tx != null)                 
                tx.rollback();          
            e.printStackTrace();
        } finally {                 
            session.close();
        }

        return retrievedPerson;
    }

    // READ CRUD Operation (recupera la lista di tutti i record nella tabella):
    @SuppressWarnings("unchecked")
    public List<Person> getPersonsList() {

        System.out.println("Inside getPersonsList()");

        Session session = sessionFactory.openSession();
        Transaction tx = null;
        List<Person> personList = null;

        try {
            tx = session.beginTransaction();
            Criteria criteria = session.createCriteria(Person.class);
            personList = criteria.list();
            System.out.println("personList: " + personList);
            tx.commit();
        }catch (HibernateException e) { 
            if (tx != null)                 
                tx.rollback();          
            e.printStackTrace();
        } finally {
            session.close();
        }
        return personList;
    }

    // DELETE CRUD Operation (elimina un singolo record avente uno specifico id):
    public void delete(int id) {

        System.out.println("Inside delete()");

        Session session = sessionFactory.openSession();
        Transaction tx = null;

        try {
            tx = session.beginTransaction();
            Person personToDelete = getById(id);
            session.delete(personToDelete);
            tx.commit();
        }catch (HibernateException e) { 
            if (tx != null)                 
                tx.rollback();          
            e.printStackTrace();
        } finally {
            session.close();
        }

    }

    @Transactional
    public void update(Person personToUpdate) {

        System.out.println("Inside update()");

        Session session = sessionFactory.openSession();
        Transaction tx = null;

        try {
            System.out.println("Insite update() method try");
            tx = session.beginTransaction();
            session.update(personToUpdate);

            tx.commit();
        }catch (HibernateException e) { 
            if (tx != null)                 
                tx.rollback();          
            e.printStackTrace();
        } finally {
            session.close();
        }   

    }

}

Ok,as you can see some methods are annoted using @Transactional annotation.

I am readin the official documentation here http://static.springsource.org/spring/docs/3.2.x/spring-framework-reference/html/transaction.html about the use of this annotation on methods and it see that: A method annoted using @Transactional must have transactional semantics but what it means with transactional semantics?

It means that the methos execution has to be considered as the execution of a transaction? So it means that the method operations have to be considered as a single operation that which may lead to a success or a failure, if successful, the results of operations has to be permanent, whereas in case of failure to return to the state prior to the start of the transaction.

Is this the meaning of use @Transactional annotation on a method?

And what exactly mean the readOnly = false attribute in the @Transactional annotation of the addPerson() method? it mean that I can also write a record in the database (and not only read it) or what? The doubt is related because I have understand that, by default, a transaction definied using @Transactional annotaion is read/write and not just read... I have also try to delete the (readOnly = false) attribute and still work well (insert the new record in the database table)

The following dout is: "why some method are annoted using @Transactional annotation and some other methods not? is it a good pratcice to annote ALL CRUD method withd @Transactional?"

Tnx

Andrea

question from:https://stackoverflow.com/questions/15300483/some-clarification-about-spring-transactional-annotation-on-a-method

Answer 1

First of all, you shouldn't make DAO methods transactional, but service methods.

Second, using Transactional is a way to let Spring start and commit/rollback transactions for you. So you shouldn't start and commit transactions yourself.

Third: this will only work if you use a transaction manager that knows how to associate a Hibernate session with the transaction (typically, a HibernateTransactionManager). The session factory should also be handled by Spring, and injected by Spring in your DAOs. The code of the DAO should look like this:

Fourth: you should not open a new session, but get the current one, associated to the current transaction by Spring.

public class PersonDAOImpl implements PersonDAO {

    @Autowired
    private SessionFactory sessionFactory;

    public Integer addPerson(Person p) {
        Session session = sessionFactory.getCurrentSession();
        Integer personID = (Integer) session.save(p);
        return personID;
    }

    public Person getById(int id) {
        Session session = sessionFactory.getCurrentSession();
        Person retrievedPerson = (Person) session.get(Person.class, id);
        return retrievedPerson;
    }

    @SuppressWarnings("unchecked")
    public List<Person> getPersonsList() {
        Session session = sessionFactory.getCurrentSession();
        Criteria criteria = session.createCriteria(Person.class);
        return criteria.list();
    }

    public void delete(int id) {
        Session session = sessionFactory.getCurrentSession();
        Person personToDelete = getById(id);
        session.delete(personToDelete);
    }

    public void update(Person personToUpdate) {
        Session session = sessionFactory.getCurrentSession();
        session.update(personToUpdate);
    }
}

Read the documentation for more information.