第五章Hibernate-OSIV与泛型DAO模式

第五章Hibernate -OSIV与泛型DAO模式

• Open Session In View（OSIV）

        使用Servlet过滤器实现OSIV模式

• 泛型DAO的设计与实现
  

            1.编写泛型DAO接口

            2.编写泛型DAO的实现类

            3.使用GenericDao接口

            4.使用GenericDaoHibernate类

•   使用Servlet过滤器实现OSIV模式

      我们使用servlet过滤器来实现自己的OSIV模式。当用户向一个JSP页面或者Servlet发出请求的时候开启Session对象，在JSP页面或者Servlet执行之后，在关闭Session对象。

    编写HibernateSessionFilter.java

public class HibernateSessionFilter implements Filter {
	private Transaction transaction = null;
    private SessionFactory sessionFactory = null;
	public void destroy() {
		sessionFactory.close();
	}

	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		try{
		Session session = sessionFactory.getCurrentSession();
		  transaction = session.beginTransaction();
		 chain.doFilter(request, response);
		 transaction.commit();
		}catch(Exception e){
			e.printStackTrace();
			try{
				if(transaction.isActive()){
					transaction.rollback();
				}
			} catch(Exception e2){
				e2.printStackTrace();
			}
		}
	}
	public void init(FilterConfig arg0) throws ServletException {
		sessionFactory = new Configuration().configure().buildSessionFactory();
	}
}

   配置web.xml

<filter>
	<filter-name>HibernateSessionFilter</filter-name>
	<filter-class>com.crazy.HibernateSessionFilter</filter-class>
</filter>
<filter-mapping>
	<filter-name>HibernateSessionFilter</filter-name>
	<url-pattern>/*</url-pattern>
</filter-mapping>

•    泛型DAO的设计与实现

      1 编写泛型DAO接口

      2 编写泛型DAO的实现类

      3 GenericDao.java

      4 GenericDaoHibernate.java

public interface GenericDao<T,PK extends Serializable> {
	public T findById(PK id);
	
	public List<T> findAll();
	
	public T save(T entity);
	
	public void update(T entity);
	
	public void delete(T entity);
}

   

public class GenericDaoHibernate<T, PK extends Serializable> implements GenericDao<T,PK> {
	private Class<T> clazz;
	
	public GenericDaoHibernate(){
		clazz = (Class<T>)((ParameterizedType)getClass().getGenericSuperclass()).getActualTypeArguments()[0];
	}

	public void delete(T entity) {
		Session session = new Configuration().configure().buildSessionFactory().openSession();
		session.delete(entity);
	}

	public List findAll() {
		Session session = new Configuration().configure().buildSessionFactory().openSession();
		Query query = session.createQuery("from" +clazz.getName());
		return query.list();
	}

	public T findById(PK id) {
		Session session = new Configuration().configure().buildSessionFactory().openSession();
		return (T)session.get(clazz, id);
	}

	public T save(T entity) {
		Session session = new Configuration().configure().buildSessionFactory().openSession();
		session.save(entity);
		return entity;
	}

	public void update(T entity) {
		Session session = new Configuration().configure().buildSessionFactory().openSession();
		session.update(entity);
	}
}

  由于Java中的泛型采用擦拭方法，因此无法直接通过反射获取到T.class。而getGenericSuperclass()方法会返回一个ParameterizedType对象，这个对象保存负累的泛型绑定参数的类型，所以通过该对象即可获取T.class。

public interface GuestbookDao extends GenericDao <Guestbook,Integer> {
	public List<Guestbook> findAllOrderById();
}

 

public class GuestbookDaoHibernate extends GenericDaoHibernate<Guestbook,Integer> implements GuestbookDao{

	public List<Guestbook> findAllOrderById() {
		Session session = new Configuration().configure().buildSessionFactory().openSession();
		Query query = session.createQuery("from Guestbook order by id desc");
		return query.list();
	}
}