java-design-patterns/service-layer/src/main/java/com/iluwatar/servicelayer/common/DaoBaseImpl.java

package com.iluwatar.servicelayer.common;

import java.lang.reflect.ParameterizedType;
import java.util.List;

import org.hibernate.Criteria;
import org.hibernate.Session;
import org.hibernate.Transaction;
import org.hibernate.criterion.Restrictions;

import com.iluwatar.servicelayer.hibernate.HibernateUtil;

/**
 * 
 * Base class for Dao implementations.
 *
 * @param <E>
 * 
 */
public abstract class DaoBaseImpl<E extends BaseEntity> implements Dao<E> {

  @SuppressWarnings("unchecked")
  protected Class<E> persistentClass = (Class<E>) ((ParameterizedType) getClass()
      .getGenericSuperclass()).getActualTypeArguments()[0];

  protected Session getSession() {
    return HibernateUtil.getSessionFactory().openSession();
  }

  @Override
  public E find(Long id) {
    Session session = getSession();
    Transaction tx = null;
    E result = null;
    try {
      tx = session.beginTransaction();
      Criteria criteria = session.createCriteria(persistentClass);
      criteria.add(Restrictions.idEq(id));
      result = (E) criteria.uniqueResult();
      tx.commit();
    } catch (Exception e) {
      if (tx != null)
        tx.rollback();
      throw e;
    } finally {
      session.close();
    }
    return result;
  }

  @Override
  public void persist(E entity) {
    Session session = getSession();
    Transaction tx = null;
    try {
      tx = session.beginTransaction();
      session.persist(entity);
      tx.commit();
    } catch (Exception e) {
      if (tx != null)
        tx.rollback();
      throw e;
    } finally {
      session.close();
    }
  }

  @Override
  public E merge(E entity) {
    Session session = getSession();
    Transaction tx = null;
    E result = null;
    try {
      tx = session.beginTransaction();
      result = (E) session.merge(entity);
      tx.commit();
    } catch (Exception e) {
      if (tx != null)
        tx.rollback();
      throw e;
    } finally {
      session.close();
    }
    return result;
  }

  @Override
  public void delete(E entity) {
    Session session = getSession();
    Transaction tx = null;
    try {
      tx = session.beginTransaction();
      session.delete(entity);
      tx.commit();
    } catch (Exception e) {
      if (tx != null)
        tx.rollback();
      throw e;
    } finally {
      session.close();
    }
  }

  @Override
  public List<E> findAll() {
    Session session = getSession();
    Transaction tx = null;
    List<E> result = null;
    try {
      tx = session.beginTransaction();
      Criteria criteria = session.createCriteria(persistentClass);
      result = criteria.list();
    } catch (Exception e) {
      if (tx != null)
        tx.rollback();
      throw e;
    } finally {
      session.close();
    }
    return result;
  }
}