Working with DAOs

The Data Access Objects for JVending are located in the provisioning-dao package. For an overview of Data Access Objects see: Wikipedia

Using DAOs from the Application Layer

The DAOs within 2.0.0-alpha2 are designed to be used at the provisioning framework level. You may, however, have custom DAOs to which you need access from the application layer. To access the HibernateDAORegistry, implement an HttpServlet and get the attribute org.jvending.registry.hibernate.HibernateDAORegistry from the ServletContext. Then invoke the find method for the DAO that you are looking for.

public void service(HttpServletRequest request, HttpServletResponse response)
                    throws IOException, ServletException {
    HibernateDAORegistry hibernateRegistry = (HibernateDAORegistry) this.getServletContext()
        .getAttribute("org.jvending.registry.hibernate.HibernateDAORegistry");
    ContentAccessorDAO contentDAO = (ContentAccessorDAO) hibernateRegistry.find("dao:content-accessor");
}

Configuring a New DAO

Before going into how to create a new DAO, let's cover the configuration. Within the registry-config.xml file, you will see the following entry

<repository>
    <repository-name>connections</repository-name>
    <repository-class>
        org.jvending.registry.hibernate.impl.Hibernate3RepositoryImpl
    </repository-class>
    <repository-config>/WEB-INF/jvending-config/connections-hsqldb.xml</repository-config>
    <init-param>
        <param-name>dao:bundle-descriptor</param-name>
        <param-value>org.jvending.provisioning.dao.impl.BundleDescriptorDAOImpl</param-value>
    </init-param>
    <init-param>
        <param-name>dao:client-bundle</param-name>
        <param-value>org.jvending.provisioning.dao.impl.ClientBundleDAOImpl</param-value>
    </init-param>
    <init-param>
        <param-name>dao:fulfillment-task</param-name>
        <param-value>org.jvending.provisioning.dao.impl.FulfillmentTaskDAOImpl</param-value>
    </init-param>
</repository>

The database connection and configuration is already set up for you. To add a new dao, put an additional init-param within the repository tag. The param-name must begin with dao: followed by the name of the dao. The param-value gives the class name of your DAO instance.

<repository>
    <repository-name>connections</repository-name>
    <repository-class>
        org.jvending.registry.hibernate.impl.Hibernate3RepositoryImpl
    </repository-class>
    <repository-config>/WEB-INF/jvending-config/connections-hsqldb.xml</repository-config>
    <init-param>
        <param-name>dao:bundle-descriptor</param-name>
        <param-value>org.jvending.provisioning.dao.impl.BundleDescriptorDAOImpl</param-value>
    </init-param>
    <init-param>
        <param-name>dao:client-bundle</param-name>
        <param-value>org.jvending.provisioning.dao.impl.ClientBundleDAOImpl</param-value>
    </init-param>
    <init-param>
        <param-name>dao:fulfillment-task</param-name>
        <param-value>org.jvending.provisioning.dao.impl.FulfillmentTaskDAOImpl</param-value>
    </init-param>
    <init-param>
        <param-name>dao:my-fancy-dao</param-name>
        <param-value>org.domainname.app.FancyDAO</param-value>
    </init-param>
</repository>

That's it for configuration. You can now access it as shown in the "Working with DAOs" section. Make sure that you cast the class to FancyDAO before using it. For more information on configuration, see Registry-J2SE - How to Use

Creating a DAO

To create a DAO, you will need to extend the org.jvending.provisioning.dao.BaseProvisioningDAO abstract class. You will need a constructor that consists of a className and id. When JVending initializes the application, it will pass in the className=org.domainname.app.FancyDAO and id=dao:my-fancy-dao. So your first stab at a valid FancyDAO class, would look something like:

    public class FancyDAO extends BaseProvisioningDAO {
        public FancyDAO(String className, String id) {
            super(className, id);
        }
    }

This class doesn't do anything, so now let's add some functionality by putting in the following method which will save our fancy objects:

    public void store(FancyObject myFancyObject) throws IOException {
        Transaction transaction = null;
        Session session = null;
        try {
            session = getSessionFactoryByName("hibernate3").openSession();
            transaction = session.beginTransaction();
            session.save(myFancyObject);
            transaction.commit();
        } catch (Exception e) {
            try {
                if (transaction != null) transaction.rollback();
            } catch (HibernateException he) {
                logger.log(Level.INFO, "Failed to roll back transaction", he);
            }
            throw new IOException();
        } finally {
            try {
                if (session != null) session.close();
            } catch (HibernateException e) {
                logger.log(Level.INFO, "Failed to close session", e);
            }
        }
    }

Notice the BaseProvisioningDAO.getSessionByName method. This class will locate and open a session for the hibernate3 datasource, which is the preconfigured one for JVending and is the datasource given in the connections-hsqldb.xml configuration file. Now you can access your DAO with all the rest of the JVending DAOs.

public void service(HttpServletRequest request, HttpServletResponse response)
                    throws IOException, ServletException {
    String fancyObjectId = request.getParameter("fancy-id");
    HibernateDAORegistry hibernateRegistry = (HibernateDAORegistry)
        this.getServletContext().getAttribute("org.jvending.registry.hibernate.HibernateDAORegistry");
    FancyDAO fancyDAO = (FancyDAO) hibernateRegistry.find("dao:my-fancy-dao");
    FancyObject fancyObject = new FancyObject();
    fancyObject.setFancyId(fancyObjectId);
    fancyDAO.store(fancyObject);
}

You can also set up your own database and database connections (separate from the one JVending uses) and reference them through the HibernateDAORegistry. On how to do this, see Registry-J2SE.