Implementing DAOs

This section shows how you can provide your own DAO implementations by using the DAO and Abstract Factory patterns. If you haven't done so already, we recommend that you first read the Persistence section in System Architecture to get an overview.

We will walk you through the necessary steps for creating the DAOs by making new DAOs that will use JDO (Java Data Object) as a persistence medium.

Note that it is not the point of this guide to show how to implement a DAO for a specific data source, so we will ommit the JDO specific parts and focus on what's necessary to create and where to plug it in.

Below you'll find the necessary steps you'll have to perform to provide your own DAO implementation.

  1. Implement BPELProcessDAO and ProcessContextDAO
  2. Implement DAOFactory
  3. Put everything on classpath
  4. Set the property

Implement BPELProcessDAO and ProcessContextDAO

Create a new file JDOBPELProcessDAO which implements the BPELProcessDAO interface.

BPELProcessDAO
public interface BPELProcessDAO {

    /**
     * Inserts a new BPELProcess.
     */
    public String insert(BPELProcess process) throws DAOException;

    /**
     * Finds a BPELProcess given its id.
     */
    public BPELProcess find(String id) throws DAOException;

    /**
     * Finds a BPELProcess given the name of its Process.
     */
    public BPELProcess findByName(String name) throws DAOException;

    /**
     * Deletes a BPELProcess given its id.
     */
    public void delete(String id) throws DAOException;

    /**
     * Updates an existing BPELProcess.
     */
    public void update(BPELProcess process) throws DAOException;
}

Do the same for the ProcessContextDAO, that is create a new file called JDOProcessContextDAO which implements the interface.

ProcessContextDAO
public interface ProcessContextDAO {

    /**
     * Inserts a new ProcessContext.
     */
    public String insert(ProcessContext ctx) throws DAOException;

    /**
     * Finds a ProcessContext given its key.
     */
    public ProcessContext find(String key) throws DAOException;

    /**
     * Deletes a ProcessContext given its key.
     */
    public void delete(String id) throws DAOException;

    /**
     * Updates an existing ProcessContext.
     */
    public void update(ProcessContext ctx) throws DAOException;
}

Implement DAOFactory

Now create a file called JDODAOFactory which extends the abstract DAOFactory class.

DAOFactory
public abstract class DAOFactory {
    /**
     * Creates a new DAOFactory. The actual type is defined by
     * the property bexee.dao.factory.
     *
     * If it is not set then MemoryDAOFactory will be created.
     */
    public static DAOFactory getInstance() {
        // implementation omitted
    }

    /**
     * The concrete factories will have to implement this method.
     */
    public abstract BPELProcessDAO createBPELProcessDAO();

    /**
     * The concrete factories will have to implement this method.
     */
    public abstract ProcessContextDAO createProcessContextDAO();
}
JDODAOFactory
public class JDODAOFactory extends DAOFactory {

    public BPELProcessDAO createBPELProcessDAO() {
        return new JDOBPELProcessDAO();
    }

    public ProcessContextDAO createProcessContextDAO() {
        return new JDOProcessContextDAO();
    }
}

Put everything on classpath

If you are building bexee from source you probably know what you're doing and can jump to the next section.

If you've downloaded a bexee binary distribution, however, you'll have to make sure that bexee will find your classes. Compile and JAR them and then put them into a directory that is on the classpath. If you are running Tomcat, then $TOMCAT_HOME$/common/lib might be a good place to drop your JAR.

Set the property

As a last step you'll have to tell bexee about the new classes to use. To do this, simply modify the bexee.dao.factory property in the bexee.properties file appropriately. Assuming that you created the classes in the bexee.dao package, the property would probably look something like this: 

bexee.dao.factory=bexee.dao.JDODAOFactoy

Alternatively you can also set a system property with the -D option: 

java ... -Dbexee.dao.factory=my.package.JDOFactory