ejbhomefactory.java

EJB Design Patterns (Code).zip

package com.portal.util;

import javax.ejb.*;
import java.rmi.*;
import javax.rmi.*;
import java.util.*;
import javax.naming.*;

/**
 * EJB Home Factory, maintains a simple hashmap cache of EJBHomes
 * For a production implementations, exceptions such as NamingException
 * can be wrapped with a factory exception to futher simplify
 * the client.
 */
public class EJBHomeFactory
{

	private Map ejbHomes;
	private static EJBHomeFactory aFactorySingleton;
	Context ctx;


	/**
	 * EJBHomeFactory private constructor.
	 */
	private EJBHomeFactory() throws NamingException
	{
        try
        {
            ctx = new InitialContext();
            this.ejbHomes = Collections.synchronizedMap(new HashMap());
        }
        catch(Exception e)
        {
            //can't do anything about this
            //client will catch errors upon trying to
            //do a lookup
        }
	}

	/*
	 * Returns the singleton instance of the EJBHomeFactory
     * The sychronized keyword is intentionally left out the
     * as I don't think the potential to intialize the singleton
     * twice at startup time (which is not a destructive event)
     * is worth creating a sychronization bottleneck on this
     * VERY frequently used class, for the lifetime of the
     * client application.
     */
	public static EJBHomeFactory getFactory() throws HomeFactoryException
	{

        try
        {
            if ( EJBHomeFactory.aFactorySingleton == null )
            {
                EJBHomeFactory.aFactorySingleton = new EJBHomeFactory();
            }

        } catch (NamingException e)
        {
            throw new HomeFactoryException(e);
        }

        return EJBHomeFactory.aFactorySingleton;
	}

	/**
	 * Lookup and cache an EJBHome object using a home class.
     * Assumes that the JNDI name of the EJB Home being looked for
     * is the same as the fully qualified class name of the
     * same EJB Home.
     * If EJB-REF tags are being used externally, then the classname
     * of the EJB Home can be mapped to the actual JNDI name of the
     * deployed bean transaprently at deployment time.
     * If EJB-REF tags are not used, then the EJB's must be deployed
     * with JNDI names equal to their fully qualified home interfaces.
     */
	public EJBHome lookUpHome(Class homeClass)
    throws HomeFactoryException
	{

		EJBHome anEJBHome;
		anEJBHome = (EJBHome) this.ejbHomes.get(homeClass);
        try
        {
            if(anEJBHome == null)
            {
                anEJBHome = (EJBHome) PortableRemoteObject.narrow
                            (ctx.lookup(homeClass.getName()), homeClass);
                this.ejbHomes.put(homeClass, anEJBHome);
            }
        }
        catch (ClassCastException e)
        {
            throw new HomeFactoryException(e);
        }
        catch (NamingException e)
        {
            throw new HomeFactoryException(e);
        }

        return anEJBHome;

	}
	/**
	 * Lookup and cache an EJBHome object.
     * This 'alternate' implementation delegates JNDI name knowledge
     * to the client. It is included here for example only.
	 */
	public EJBHome lookUpHome(Class homeClass, String jndiName)
    throws HomeFactoryException
	{

		EJBHome anEJBHome;

		anEJBHome = (EJBHome) this.ejbHomes.get(homeClass);

        try
        {
            if(anEJBHome == null)
            {
                System.out.println("finding HOME for first time");
                anEJBHome = (EJBHome) PortableRemoteObject.narrow
                            ( ctx.lookup (jndiName), homeClass);
                this.ejbHomes.put(homeClass, anEJBHome);
            }
        }
        catch (ClassCastException e)
        {
            throw new HomeFactoryException(e);
        }
        catch (NamingException e)
        {
            throw new HomeFactoryException(e);
        }

		return anEJBHome;		
		
	}

}