Factory Service

The Factory Service instantiates objects from the given class name using either the given class loader or an applicable one found from the class loader repository. If neither one is specified, the default class loader will be used.

The service provides the following benefits compared to Class.forName():

  • support for parameters in constructors,
  • internal class loader repository, which can be specified in resources,
  • optional class specific factories, which can be used for customized instantiation, and
  • integration with the Pool Service supporting recycling of instances created by the service.

Configuration

# -------------------------------------------------------------------
#
#  S E R V I C E S
#
# -------------------------------------------------------------------
# Classes for Turbine Services should be defined here.
# Format: services.[name].classname=[implementing class]
#
# To specify properties of a service use the following syntax:
# service.[name].[property]=[value]

services.FactoryService.classname=org.apache.turbine.services.factory.TurbineFactoryService
.
.
.
# -------------------------------------------------------------------
#
#  F A C T O R Y  S E R V I C E
#
# -------------------------------------------------------------------

# A comma separated list of classloaders (very optional)
#
# Example: org.foo.bar.MyClassLoader, org.ack.joe.YourClassLoader
#
#services.FactoryService.class.loaders=

# Customized factories to be used instead of the default factory.
# E.g. to instantiate XML parsers, SSL sockets, etc., which require
# specific instantiation not supported by the default factory.
# The property name is prefixed with "factory" followed by the
# name of the production class. The value is the class name of
# the factory implementing the Factory interface. The factory
# will be instantiated by using the service itself.
#
# Examples:
#
#services.FactoryService.factory.javax.xml.parsers.DocumentBuilder=org.foo.xml.DomBuilderFactory
#services.FactoryService.factory.javax.xml.parsers.SAXParser=org.foo.xml.SaxParserFactory
#services.FactoryService.factory.java.net.ServerSocket=org.foo.net.SslServerSocketFactory

Usage

In Turbine, the Factory Service is currently only used internally by the Pool Service. Applications can also use the service instead of Class.forName() and for unifying initialization, configuration and access to vendor specific object factories. The following is a simplified example of a customized DOM parser factory: 

package org.foo.xml;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.apache.turbine.util.TurbineException;
import org.apache.turbine.services.factory.Factory;

/**
 * A factory for instantiating DOM parsers.
 */
public class DomBuilderFactory implements Factory
{
    /**
     * The implementation of the factory.
     */
    private DocumentBuilderFactory factory;

    /**
     * Initializes the factory.
     */
    public void init(String className)
        throws TurbineException
    {
        factory = DocumentBuilderFactory.newInstance();
    }

    /**
     * Gets a DocumentBuilder instance.
     */
    public Object getInstance()
        throws TurbineException
    {
        try
        {
            return factory.newDocumentBuilder();
        }
        catch (ParserConfigurationException x)
        {
            throw new TurbineException(x);
        }
    }

    /**
     * Gets a DocumentBuilder instance.
     * The given loader is ignored.
     */
    public Object getInstance(ClassLoader loader)
        throws TurbineException
    {
        return getInstance();
    }

    /**
     * Gets a DocumentBuilder instance.
     * Constructor parameters are ignored.
     */
    public Object getInstance(Object[] params,
                              String[] signature)
        throws TurbineException
    {
        return getInstance();
    }

    /**
     * Gets a DocumentBuilder instance.
     * The given loader and constructor parameters are ignored.
     */
    public Object getInstance(ClassLoader loader,
                              Object[] params,
                              String[] signature)
        throws TurbineException
    {
        return getInstance();
    }

    /**
     * Returns false as given class loaders are not supported.
     */
    public boolean isLoaderSupported()
    {
        return false;
    }
}

The customized DOM parser factory must be specified in Turbine Resources before it can be used: 

services.FactoryService.factory.javax.xml.parsers.DocumentBuilder=org.foo.xml.DomBuilderFactory

A DOM parser can now be instantiated with the following code fragment: 

// Access the service singleton.
FactoryService service = (FactoryService)
    TurbineServices.getInstance().getService(FactoryService.SERVICE_NAME);

// Create a new DOM parser.
DocumentBuilder parser =
    service.getInstance("javax.xml.parsers.DocumentBuilder");