extending.fm3.html

IMAGEIO package 的使用说明jdk1.4新出的 包。有效改进图片读写方式。

	} else {
		processImageComplete(imageIndex);
	}

	// If the read was aborted, we still return a partially decoded image
	return theImage;
}
</pre></blockquote>

<blockquote>
<a name="1001105"><!-- --></a>
<i><b> Metadata
</b></i>
</blockquote>
<blockquote>
<a name="1001097"><!-- --></a>
The next set of methods in <code>MyFormatImageReader</code> deal with metadata. Because our hypothetical format only encodes a single image, we may ignore the concept of &#34;stream&#34; metadata, and use &#34;image&#34; metadata only:<p>
</blockquote><blockquote><pre>
	MyFormatMetadata metadata = null; // class defined below

	public IIOMetadata getStreamMetadata()
		throws IIOException {
		return null;
	}

	public IIOMetadata getImageMetadata(int imageIndex)
		throws IIOException {
		if (imageIndex != 0) {
			throw new IndexOutOfBoundsException(&#34;imageIndex != 0!&#34;);
		}
		readMetadata();
		return metadata;
	}

</pre></blockquote><blockquote>
<a name="997606"><!-- --></a>
The actual work is done by a format-specific method <code>readMetadata</code>, which for this format fills in the keyword/value pairs of the metadata object,<p>
</blockquote><blockquote><pre>
	public void readMetadata() throws IIOException {
		if (metadata != null) {
			return;
		}
		readHeader();
		this.metadata = new MyFormatMetadata();
		try {
			while (true) {
				String keyword = stream.readUTF();
				stream.readUnsignedByte();
				if (keyword.equals(&#34;END&#34;)) {
					break;
				}
				String value = stream.readUTF();
				stream.readUnsignedByte();

				metadata.keywords.add(keyword);
				metadata.values.add(value);
			} catch (IIOException e) {
				throw new IIOException(&#34;Exception reading metadata&#34;,
				                       e);
			}
		}
	}<code>
</code></pre></blockquote>

<blockquote>
<a name="1001093"><!-- --></a>
<i><b> <code>MyFormatMetadata</code>
</b></i>
</blockquote>
<blockquote>
<a name="997208"><!-- --></a>
Finally, the various interfaces for extracting and editing metadata must be defined. We define a class called <code>MyFormatMetadata</code> that extends the <code>IIOMetadata</code> class, and additionally can store the keyword/value pairs that are allowed in the file format:<p>
</blockquote><blockquote><pre>
package com.mycompany.imageio;

import org.w3c.dom.*;
import javax.xml.parsers.*; // Package name may change in JDK 1.4

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import javax.imageio.metadata.IIOInvalidTreeException;
import javax.imageio.metadata.IIOMetadata;
import javax.imageio.metadata.IIOMetadataFormat;
import javax.imageio.metadata.IIOMetadataNode;

public class MyFormatMetadata extends IIOMetadata {

	static final boolean standardMetadataFormatSupported = false;
	static final String nativeMetadataFormatName =
		"com.mycompany.imageio.MyFormatMetadata_1.0";
	static final String nativeMetadataFormatClassName =
		"com.mycompany.imageio.MyFormatMetadata";
	static final String[] extraMetadataFormatNames = null;
	static final String[] extraMetadataFormatClassNames = null;
    
	// Keyword/value pairs
	List keywords = new ArrayList();
	List values = new ArrayList();
</pre></blockquote><blockquote>
<a name="998826"><!-- --></a>
The first set of methods are common to most IIOMetadata implementations:<p>
</blockquote><blockquote><pre>
	public MyFormatMetadata() {
		super(standardMetadataFormatSupported,
		      nativeMetadataFormatName,
		      nativeMetadataFormatClassName,
		      extraMetadataFormatNames,
		      extraMetadataFormatClassNames);
	}

	public IIOMetadataFormat getMetadataFormat(String formatName) {
		if (!formatName.equals(nativeMetadataFormatName)) {
			throw new IllegalArgumentException("Bad format name!");
		}
		return MyFormatMetadataFormat.getDefaultInstance();
	}

</pre></blockquote><blockquote>
<a name="998828"><!-- --></a>
The most important method for reader plug-ins is <code>getAsTree</code>:<p>
</blockquote><blockquote><pre>
	public Node getAsTree(String formatName) {
		if (!formatName.equals(nativeMetadataFormatName)) {
			throw new IllegalArgumentException("Bad format name!");
		}

		// Create a root node
		IIOMetadataNode root =
			new IIOMetadataNode(nativeMetadataFormatName);

		// Add a child to the root node for each keyword/value pair
		Iterator keywordIter = keywords.iterator();
		Iterator valueIter = values.iterator();
		while (keywordIter.hasNext()) {
			IIOMetadataNode node =
				new IIOMetadataNode(&#34;KeywordValuePair&#34;);
			node.setAttribute(&#34;keyword&#34;, (String)keywordIter.next());
			node.setAttribute(&#34;value&#34;, (String)valueIter.next());
			root.appendChild(node);
		}

		return root;
	}
</pre></blockquote><blockquote>
<a name="998830"><!-- --></a>
For writer plug-ins, the ability to edit metadata values is obtained by implementing the <code>isReadOnly</code>, <code>reset</code>, and <code>mergeTree</code> methods:<p>
</blockquote><blockquote><pre>
	public boolean isReadOnly() {
	    return false;
	}

	public void reset() {
	    this.keywords = new ArrayList();
	    this.values = new ArrayList();
	}

	public void mergeTree(String formatName, Node root)
		throws IIOInvalidTreeException {
		if (!formatName.equals(nativeMetadataFormatName)) {
			throw new IllegalArgumentException("Bad format name!");
		}

		Node node = root;
		if (!node.getNodeName().equals(nativeMetadataFormatName)) {
			fatal(node, &#34;Root must be &#34; + nativeMetadataFormatName);
		}
		node = node.getFirstChild();
		while (node != null) {
			if (!node.getNodeName().equals(&#34;KeywordValuePair&#34;)) {
				fatal(node, &#34;Node name not KeywordValuePair!&#34;);
			}
			NamedNodeMap attributes = node.getAttributes();
			Node keywordNode = attributes.getNamedItem(&#34;keyword&#34;);
			Node valueNode = attributes.getNamedItem(&#34;value&#34;);
			if (keywordNode == null || valueNode == null) {
				fatal(node, &#34;Keyword or value missing!&#34;);
			}

			// Store keyword and value
			keywords.add((String)keywordNode.getNodeValue());
			values.add((String)valueNode.getNodeValue());

			// Move to the next sibling
			node = node.getNextSibling();
		}
	}

	private void fatal(Node node, String reason)
		throws IIOInvalidTreeException {
		throw new IIOInvalidTreeException(reason, node);
	}
}
</pre></blockquote>

<blockquote>
<a name="996881"><!-- --></a>
<i><b> <code>MyFormatMetadataFormat</code>
</b></i>
</blockquote>
<blockquote>
<a name="999065"><!-- --></a>
The tree structure of the metadata may be described using the IIOMetadataFormat interface. An implementation class, IIOMetadataFormatImpl, takes care of maintaining the &#34;database&#34; of information about elements, their attributes, and the parent-child relationships between them:<p>
</blockquote><blockquote><pre>
package com.mycompany.imageio;

import javax.imageio.ImageTypeSpecifier;
import javax.imageio.metadata.IIOMetadataFormatImpl;

public class MyFormatMetadataFormat extends IIOMetadataFormatImpl {

	// Create a single instance of this class (singleton pattern)
	private static MyFormatMetadataFormat defaultInstance =
		new MyFormatMetadataFormat();

	// Make constructor private to enforce the singleton pattern
	private MyFormatMetadataFormat() {
		// Set the name of the root node
		// The root node has a single child node type that may repeat
		super(&#34;com.mycompany.imageio.MyFormatMetadata_1.0&#34;,
		      CHILD_POLICY_REPEAT);

		// Set up the &#34;KeywordValuePair&#34; node, which has no children
		addElement(&#34;KeywordValuePair&#34;,
		           &#34;com.mycompany.imageio.MyFormatMetadata_1.0&#34;,
		           CHILD_POLICY_EMPTY);

		// Set up attribute &#34;keyword&#34; which is a String that is required
		// and has no default value
		addAttribute(&#34;KeywordValuePair&#34;, &#34;keyword&#34;, DATATYPE_STRING,
		             true, null);
		// Set up attribute &#34;value&#34; which is a String that is required
		// and has no default value
		addAttribute(&#34;KeywordValuePair&#34;, &#34;value&#34;, DATATYPE_STRING,
		             true, null);
	}

	// Check for legal element name
	public boolean canNodeAppear(String elementName,
	                             ImageTypeSpecifier imageType) {
		return elementName.equals(&#34;KeywordValuePair&#34;);
	}

	// Return the singleton instance
	public static MyFormatMetadataFormat getDefaultInstance() {
		return defaultInstance;
	}
}
</pre></blockquote><blockquote>
<a name="999124"><!-- --></a>
<p>
</blockquote>

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