dynamicimageresource.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.markup.html.image.resource;

import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.util.Locale;

import javax.imageio.ImageIO;

import org.apache.wicket.WicketRuntimeException;
import org.apache.wicket.markup.html.DynamicWebResource;
import org.apache.wicket.util.time.Time;


/**
 * An ImageResource subclass for dynamic images (images created programmatically). Subclasses
 * override getImageData() to provide the image data to send back to the user. A given subclass may
 * decide how to produce this data and whether/how to buffer it.
 * <p>
 * The RenderedDynamicImageResource subclass is designed for images that can be regenerated when the
 * component is deserialized (the image data is transient). A good example of a
 * RenderedDynamicImageResource is the DefaultButtonImageResource class, which can regenerate a
 * given button image at any time. This makes it very lightweight when clustered. The
 * BufferedDynamicImageResource class, on the other hand, is designed for images that cannot be
 * regenerated on demand. It buffers its image data in a non-transient way, which means that the
 * entire image will be serialized and copied when the resource is replicated in a cluster!
 * <p>
 * The helper method toImageData(BufferedImage) is provided so that subclasses can easily turn a
 * BufferedImage into a suitable return value when implementing getImageData().
 * <p>
 * The format of the image (and therefore the resource's extension) can be specified with
 * setFormat(String). The default format is "PNG" because JPEG is lossy and makes generated images
 * look bad and GIF has patent issues.
 * 
 * @author Jonathan Locke
 * @author Gili Tzabari
 * @author Johan Compagner
 */
public abstract class DynamicImageResource extends DynamicWebResource
{
	/**
	 * 
	 */
	private static final long serialVersionUID = 1L;

	/** The image type */
	private String format = "png";

	/** The last modified time of this resource */
	private Time lastModifiedTime;

	/**
	 * Creates a dynamic image resource.
	 */
	public DynamicImageResource()
	{
	}

	/**
	 * Creates a dynamic resource from for the given locale
	 * 
	 * @param locale
	 *            The locale of this resource
	 */
	public DynamicImageResource(Locale locale)
	{
		super(locale);
	}

	/**
	 * Creates a dynamic resource from for the given locale
	 * 
	 * @param format
	 *            The image format ("png", "jpeg", etc)
	 */
	public DynamicImageResource(String format)
	{
		setFormat(format);
	}

	/**
	 * Creates a dynamic resource from for the given locale
	 * 
	 * @param format
	 *            The image format ("png", "jpeg", etc)
	 * @param locale
	 *            The locale of this resource
	 */
	public DynamicImageResource(String format, Locale locale)
	{
		super(locale);
		setFormat(format);
	}

	/**
	 * @return Returns the image format.
	 */
	public synchronized final String getFormat()
	{
		return format;
	}

	/**
	 * Sets the format of this resource
	 * 
	 * @param format
	 *            The format (jpg, png or gif..)
	 */
	public synchronized final void setFormat(String format)
	{
		this.format = format;
	}

	/**
	 * set the last modified time for this resource.
	 * 
	 * @param time
	 */
	protected synchronized void setLastModifiedTime(Time time)
	{
		lastModifiedTime = time;
	}

	/**
	 * @param image
	 *            The image to turn into data
	 * @return The image data for this dynamic image
	 */
	protected byte[] toImageData(final BufferedImage image)
	{
		try
		{
			// Create output stream
			final ByteArrayOutputStream out = new ByteArrayOutputStream();

			// Write image using any matching ImageWriter
			ImageIO.write(image, format, out);

			// Return the image data
			return out.toByteArray();
		}
		catch (IOException e)
		{
			throw new WicketRuntimeException("Unable to convert dynamic image to stream", e);
		}
	}

	/**
	 * @see DynamicWebResource#getResourceState()
	 */
	protected synchronized ResourceState getResourceState()
	{
		return new ResourceState()
		{
			private byte[] imageData;
			private final String contentType = "image/" + format;

			public Time lastModifiedTime()
			{
				if (lastModifiedTime == null)
				{
					lastModifiedTime = DynamicImageResource.this.lastModifiedTime;
					if (lastModifiedTime == null)
					{
						lastModifiedTime = Time.now();
					}
				}
				return lastModifiedTime;
			}

			public byte[] getData()
			{
				if (imageData == null)
				{
					imageData = getImageData();
				}
				return imageData;
			}

			public String getContentType()
			{
				return contentType;
			}
		};
	}

	/**
	 * Get image data for our dynamic image resource. If the subclass regenerates the data, it
	 * should set the lastModifiedTime when it does so. This ensures that image caching works
	 * correctly.
	 * 
	 * @return The image data for this dynamic image
	 */
	protected abstract byte[] getImageData();
}