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Wicket is a Java web application framework that takes simplicity, separation of concerns and ease of development to a whole new level. Wicket pages can be mocked up, previewed and later revised using standard WYSIWYG HTML design tools. Dynamic content processing and form handling is all handled in Java code using a first-class component model backed by POJO data beans that can easily be persisted using your favorite technology.

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/*
 * 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;


import org.apache.wicket.util.io.IClusterable;

/**
 * A key to a piece of metadata associated with a {@link Component}, {@link Session} or
 * {@link Application} at runtime. The key contains type information that can be used to check the
 * type of any metadata value for the key when the value is set. MetaDataKey is abstract in order to
 * force the creation of a subtype. That subtype is used to test for identity when looking for the
 * metadata because actual object identity would suffer from problems under serialization. So, the
 * correct way to declare a MetaDataKey is like this:
 * 
 *  * 
 * public static final MetaDataKey<Role> ROLE = new MetaDataKey<Role>() { };
 * 
 * 
 * 
 * @author Jonathan Locke
 * 
 * @param 
 *            The type of the object which is stored
 * 
 * @see Session#getMetaData(MetaDataKey)
 * @see Component#getMetaData(MetaDataKey)
 * @see Application#getMetaData(MetaDataKey)
 */
public abstract class MetaDataKey implements IClusterable
{
	private static final long serialVersionUID = 1L;

	/**
	 * Constructor.
	 */
	public MetaDataKey()
	{
	}

	@Override
	public int hashCode()
	{
		return getClass().hashCode();
	}

	/**
	 * @see java.lang.Object#equals(java.lang.Object)
	 */
	@Override
	public boolean equals(Object obj)
	{
		return obj != null && getClass().equals(obj.getClass());
	}

	/**
	 * @param metaData
	 *            Array of metadata to search
	 * @return The entry value
	 */
	@SuppressWarnings("unchecked")
	public T get(MetaDataEntry[] metaData)
	{
		if (metaData != null)
		{
			for (MetaDataEntry entry : metaData)
			{
				if (equals(entry.key))
				{
					return (T)entry.object;
				}
			}
		}
		return null;
	}

	/**
	 * @param metaData
	 *            The array of metadata
	 * @param object
	 *            The object to set, null to remove
	 * @return Any new metadata array (if it was reallocated)
	 */
	public MetaDataEntry[] set(MetaDataEntry[] metaData, final Object object)
	{
		boolean set = false;
		if (metaData != null)
		{
			for (int i = 0; i < metaData.length; i++)
			{
				MetaDataEntry m = metaData[i];
				if (equals(m.key))
				{
					if (object != null)
					{
						// set new value
						m.object = object;
					}
					else
					{
						// remove value and shrink or null array
						if (metaData.length > 1)
						{
							int l = metaData.length - 1;
							MetaDataEntry[] newMetaData = new MetaDataEntry[l];
							System.arraycopy(metaData, 0, newMetaData, 0, i);
							System.arraycopy(metaData, i + 1, newMetaData, i, l - i);
							metaData = newMetaData;
						}
						else
						{
							metaData = null;
						}
					}
					set = true;
					break;
				}
			}
		}
		if (!set && object != null)
		{
			MetaDataEntry m = new MetaDataEntry(this, object);
			if (metaData == null)
			{
				metaData = new MetaDataEntry[1];
				metaData[0] = m;
			}
			else
			{
				final MetaDataEntry[] newMetaData = new MetaDataEntry[metaData.length + 1];
				System.arraycopy(metaData, 0, newMetaData, 0, metaData.length);
				newMetaData[metaData.length] = m;
				metaData = newMetaData;
			}
		}
		return metaData;
	}

	/**
	 * @see java.lang.Object#toString()
	 */
	@Override
	public String toString()
	{
		return getClass().toString();
	}
}