jcckit.util.Factory Maven / Gradle / Ivy
/*
* Copyright 2003-2004, Franz-Josef Elmer, All rights reserved
*
* This library is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser General Public License as published by
* the Free Software Foundation; either version 2.1 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details
* (http://www.gnu.org/copyleft/lesser.html).
*
* You should have received a copy of the GNU Lesser General Public License
* along with this library; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
package jcckit.util;
import java.lang.reflect.Constructor;
/**
* General purpose factory method based on {@link ConfigParameters}
* and Java's Reflection API.
*
* @author Franz-Josef Elmer
*/
public class Factory {
/** The constant defining the key className. */
public static final String CLASS_NAME_KEY = "className";
/** No public constructor necessary. */
private Factory() {}
/**
* Creates an instance of the specified class.
* @param className Fully-qualified name of a class with a default
* constructor.
* @return a new instance.
* @throws IllegalArgumentException if the instance could be created.
*/
public static Object create(String className) {
try {
return Class.forName(className).newInstance();
} catch (Throwable t) {
throw new IllegalArgumentException("Could not create an instance of "
+ className + " because of " + t);
}
}
/**
* Creates an object based on the specified configuration
* parameters. The class of the object is determined by the
* parameter with the key {@link #CLASS_NAME_KEY}.
* The constructor with a single argument of the type
* ConfigParameter is invoked with the argument
* configParameters. If such a constructor
* does not exists the default constructor is invoked. If
* neither of these constructors exist a {@link FactoryException}
* is thrown.
* @param configParameters Configuration parameters.
* @return the newly created object.
* @throws IllegalArgumentException if key className is missing.
* @throws FactoryException wrapping any kind of exception or error occured.
*/
public static Object create(ConfigParameters configParameters) {
String className = configParameters.get(CLASS_NAME_KEY);
return createObject(configParameters, className);
}
/**
* Creates an object based on the specified configuration
* parameters and default class name. If the
* parameter with the key {@link #CLASS_NAME_KEY} is missed in
* configParameters defaultClassName is used.
* Otherwise it works as {@link #create(jcckit.util.ConfigParameters)}.
* @param configParameters Configuration parameters.
* @param defaultClassName Default class name.
* @return the newly created object.
* @throws FactoryException wrapping any kind of exception or error occured.
*/
public static Object create(ConfigParameters configParameters,
String defaultClassName) {
String className = configParameters.get(CLASS_NAME_KEY, defaultClassName);
return createObject(configParameters, className);
}
/**
* Creates an object based on the specified configuration
* parameters or returns the default object. This method behaves
* as {@link #create(jcckit.util.ConfigParameters)}, except that is does
* not throw an IllegalArgumentException if key className
* is missing. Instead defaultObject is returned.
*/
public static Object createOrGet(ConfigParameters configParameters,
Object defaultObject) {
String className = configParameters.get(CLASS_NAME_KEY, null);
return className == null ? defaultObject
: createObject(configParameters, className);
}
private static Object createObject(ConfigParameters configParameters,
String className) {
try {
Class c = Class.forName(className);
Object result = null;
Constructor constructor = null;
try {
constructor = c.getConstructor(new Class[] {ConfigParameters.class});
result = constructor.newInstance(new Object[] {configParameters});
} catch (NoSuchMethodException e) {
result = c.newInstance();
}
return result;
} catch (Throwable t) {
throw new FactoryException(configParameters, CLASS_NAME_KEY, t);
}
}
}