loadabledetachablemodel.java

Wicket一个开发Java Web应用程序框架。它使得开发web应用程序变得容易而轻松。 Wicket利用一个POJO data beans组件使得它可以与任何持久层技术相结合。

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.wicket.model;

import org.apache.wicket.Component;
import org.apache.wicket.RequestCycle;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;


/**
 * Model that makes working with detachable models a breeze. LoadableDetachableModel holds a
 * temporary, transient model object, that is set when {@link #getObject(Component)} is called by
 * calling abstract method 'load', and that will be reset/ set to null on {@link #detach()}.
 * 
 * A usage example:
 * 
 * <pre>
 * LoadableDetachableModel venueListModel = new LoadableDetachableModel()
 * {
 * 	protected Object load()
 * 	{
 * 		return getVenueDao().findVenues();
 * 	}
 * };
 * </pre>
 * 
 * <p>
 * Though you can override methods {@link #onAttach()} and {@link #onDetach()} for additional
 * attach/ detach behavior, the point of this class is to hide as much of the attaching/ detaching
 * as possible. So you should rarely need to override those methods, if ever.
 * </p>
 * 
 * @author Eelco Hillenius
 * @author Igor Vaynberg
 */
public abstract class LoadableDetachableModel extends AbstractReadOnlyModel
{
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	/** Logger. */
	private static final Logger log = LoggerFactory.getLogger(LoadableDetachableModel.class);

	/** keeps track of whether this model is attached or detached */
	private transient boolean attached = false;

	/** temporary, transient object. */
	private transient Object transientModelObject;

	/**
	 * Construct.
	 */
	public LoadableDetachableModel()
	{
	}

	/**
	 * This constructor is used if you already have the object retrieved and want to wrap it with a
	 * detachable model.
	 * 
	 * @param object
	 *            retrieved instance of the detachable object
	 */
	public LoadableDetachableModel(Object object)
	{
		this.transientModelObject = object;
		attached = true;
	}

	/**
	 * @see org.apache.wicket.model.IDetachable#detach()
	 */
	public void detach()
	{
		if (attached)
		{
			attached = false;
			transientModelObject = null;

			if (log.isDebugEnabled())
			{
				log.debug("removed transient object for " + this + ", requestCycle " +
						RequestCycle.get());
			}
			onDetach();
		}
	}

	/**
	 * @see org.apache.wicket.model.IModel#getObject()
	 */
	public Object getObject()
	{
		if (!attached)
		{
			attached = true;
			transientModelObject = load();

			if (log.isDebugEnabled())
			{
				log.debug("loaded transient object " + transientModelObject + " for " + this +
						", requestCycle " + RequestCycle.get());
			}

			onAttach();
		}
		return transientModelObject;
	}

	/**
	 * Gets the attached status of this model instance
	 * 
	 * @return true if the model is attached, false otherwise
	 */
	public final boolean isAttached()
	{
		return attached;
	}

	/**
	 * @see java.lang.Object#toString()
	 */
	public String toString()
	{
		StringBuffer sb = new StringBuffer(super.toString());
		sb.append(":attached=").append(attached).append(":tempModelObject=[").append(
				this.transientModelObject).append("]");
		return sb.toString();
	}

	/**
	 * Loads and returns the (temporary) model object.
	 * 
	 * @return the (temporary) model object
	 */
	protected abstract Object load();

	/**
	 * Attaches to the current request. Implement this method with custom behavior, such as loading
	 * the model object.
	 */
	protected void onAttach()
	{
	}

	/**
	 * Detaches from the current request. Implement this method with custom behavior, such as
	 * setting the model object to null.
	 */
	protected void onDetach()
	{
	}
}