wicket-spring/src/main/java/wicket/injection/Injector.java

/*
 * $Id$
 * $Revision$
 * $Date$
 * 
 * ==============================================================================
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package wicket.injection;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.List;

import wicket.Component;
import wicket.MarkupContainer;
import wicket.Page;
import wicket.markup.html.WebPage;
import wicket.markup.html.panel.Panel;
import wicket.util.concurrent.ConcurrentHashMap;

/**
 * Injector scans fields of an object instance and checks if the specified
 * {@link IFieldValueFactory} can provide a value for a field; if it can, the
 * field is set to that value. Injector will ignore all non-null fields.
 * 
 * @author Igor Vaynberg (ivaynberg)
 * 
 */
public class Injector
{
	private static Injector instance = new Injector();

	private ConcurrentHashMap/* <Class, Field[]> */classToFields = new ConcurrentHashMap();

	/**
	 * @return static instance of ProxyInjector
	 */
	public static Injector getInstance()
	{
		return instance;
	}

	/**
	 * When the initializer traverses the hierarchy of the specified object it
	 * will stop if it encounters a boundary class.
	 * 
	 * By default, more common wicket classes are defined as boundaries so that
	 * the initializer does not waste time traversing them.
	 * 
	 * @param clazz
	 *            class to be tested for being a boundary class
	 * @return true if the class is a boundary class, false otherwise
	 */
	protected boolean isBoundaryClass(Class clazz)
	{
		if (clazz.equals(WebPage.class)
				|| clazz.equals(Page.class) || clazz.equals(Panel.class)
				|| clazz.equals(MarkupContainer.class) || clazz.equals(Component.class))
		{
			return true;
		}
		return false;
	}

	/**
	 * traverse fields in the class hierarchy of the object and set their value
	 * with a locator provided by the locator factory.
	 * 
	 * @param object
	 * @param factory
	 * @return Object that was injected - used for chaining
	 */
	public Object inject(Object object, IFieldValueFactory factory)
	{
		Class clazz = object.getClass();
		Field[] fields;

		fields = (Field[]) classToFields.get(clazz);
		if (fields == null)
		{
			fields = findFields(clazz, factory);
			classToFields.put(clazz, fields);
		}

		for (int i = 0; i < fields.length; i++)
		{
			final Field field = fields[i];

			if (!field.isAccessible())
			{
				field.setAccessible(true);
			}
			try
			{

				if (field.get(object) == null)
				{

					Object value = factory.getFieldValue(field, object);

					if (value != null)
					{
						field.set(object, value);
					}
				}
			}
			catch (IllegalArgumentException e)
			{
				throw new RuntimeException("error while injecting object ["
						+ object.toString() + "] of type [" + object.getClass().getName()
						+ "]", e);
			}
			catch (IllegalAccessException e)
			{
				throw new RuntimeException("error while injecting object ["
						+ object.toString() + "] of type [" + object.getClass().getName()
						+ "]", e);
			}
		}

		return object;
	}

	/**
	 * Returns an array of fields that can be injected using the given field
	 * value factory
	 * 
	 * @param clazz
	 * @param factory
	 * @return an array of fields that can be injected using the given field
	 *         value factory
	 */
	private Field[] findFields(Class clazz, IFieldValueFactory factory)
	{
		List/* <Field> */matched = new ArrayList();

		while (clazz != null && !isBoundaryClass(clazz))
		{
			Field[] fields = clazz.getDeclaredFields();
			for (int i = 0; i < fields.length; i++)
			{
				final Field field = fields[i];

				if (factory.supportsField(field))
				{
					matched.add(field);
				}
			}
			clazz = clazz.getSuperclass();
		}

		return (Field[]) matched.toArray(new Field[matched.size()]);
	}

}