pre-wicket.1.2.5/wicket-spring-annot/src/main/java/wicket/spring/injection/annot/AnnotProxyFieldValueFactory.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.spring.injection.annot;

import java.lang.reflect.Field;
import java.util.concurrent.ConcurrentHashMap;

import wicket.injection.IFieldValueFactory;
import wicket.proxy.LazyInitProxyFactory;
import wicket.spring.ISpringContextLocator;
import wicket.spring.SpringBeanLocator;

/**
 * {@link IFieldValueFactory} that uses {@link LazyInitProxyFactory} to create proxies for Spring
 * dependencies based on the {@link SpringBean} annotation applied to a field.
 * This class is usually used by the {@link AnnotSpringInjector} to inject
 * objects with lazy init proxies. However, this class can be used on its own to
 * create proxies for any field decorated with a {@link SpringBean} annotation.
 * <p>
 * Example:
 * 
 * <pre>
 * IFieldValueFactory factory = new AnnotProxyFieldValueFactory(contextLocator);
 * field = obj.getClass().getDeclaredField(&quot;dependency&quot;);
 * IDependency dependency = (IDependency) factory.getFieldValue(field, obj);
 * </pre>
 * 
 * In the example above the <code>dependency</code> object returned is a lazy init proxy
 * that will look up the actual IDependency bean from spring context upon first
 * access to one of the methods.
 * <p>
 * This class will also cache any produced proxies so that the same proxy is
 * always returned for the same spring dependency. This helps cut down on
 * session size beacause proxies for the same dependency will not be serialized
 * twice.
 * 
 * @see LazyInitProxyFactory
 * @see SpringBean
 * @see SpringBeanLocator
 * 
 * @author Igor Vaynberg (ivaynberg)
 * 
 */
public class AnnotProxyFieldValueFactory implements IFieldValueFactory
{
	private ISpringContextLocator contextLocator;

	private final ConcurrentHashMap<SpringBeanLocator, Object> cache = new ConcurrentHashMap<SpringBeanLocator, Object>();

	/**
	 * @param contextLocator
	 *            spring context locator
	 */
	public AnnotProxyFieldValueFactory(ISpringContextLocator contextLocator)
	{
		if (contextLocator == null)
		{
			throw new IllegalArgumentException("[contextLocator] argument cannot be null");
		}
		this.contextLocator = contextLocator;
	}

	/**
	 * @see wicket.injection.IFieldValueFactory#getFieldValue(java.lang.reflect.Field,
	 *      java.lang.Object)
	 */
	public Object getFieldValue(Field field, Object fieldOwner)
	{

		if (field.isAnnotationPresent(SpringBean.class))
		{
			SpringBean annot = field.getAnnotation(SpringBean.class);
			SpringBeanLocator locator = new SpringBeanLocator(annot.name(), field
					.getType(), contextLocator);

			if (cache.containsKey(locator))
			{
				return cache.get(locator);
			}

			// fail early - see if the locator can locate the spring bean
			testLocator(locator, fieldOwner, field);
			
			Object proxy = LazyInitProxyFactory.createProxy(field.getType(), locator);
			cache.put(locator, proxy);
			return proxy;
		}
		else
		{
			return null;
		}
	}
	
	/**
	 * Tests if the locator can retrieve the bean it is responsible for.
	 * 
	 * @param locator
	 * @param fieldOwner
	 * @param field
	 */
	private void testLocator(SpringBeanLocator locator, Object fieldOwner, Field field)
	{
		try
		{
			locator.locateProxyTarget();
		}
		catch (Throwable e)
		{
			String errorMessage = "Could not locate spring bean of class [["
					+ locator.getBeanType().getName() + "]] ";
			if (locator.getBeanName() != null && locator.getBeanName().length() > 0)
			{
				errorMessage += "and id [[" + locator.getBeanName() + "]] ";
			}
			errorMessage += "needed in class [["
					+ fieldOwner.getClass().getName() + "]] field [[" + field.getName()
					+ "]]";
			throw new RuntimeException(errorMessage, e);
		}
	}


	/**
	 * @see wicket.injection.IFieldValueFactory#supportsField(java.lang.reflect.Field)
	 */
	public boolean supportsField(Field field)
	{
		return field.isAnnotationPresent(SpringBean.class);
	}

}