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/* * Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package javax.imageio.metadata; import org.w3c.dom.Node; import java.lang.reflect.Method; import java.security.AccessController; import java.security.PrivilegedAction; /** * An abstract class to be extended by objects that represent metadata * (non-image data) associated with images and streams. Plug-ins * represent metadata using opaque, plug-in specific objects. These * objects, however, provide the ability to access their internal * information as a tree of {@code IIOMetadataNode} objects that * support the XML DOM interfaces as well as additional interfaces for * storing non-textual data and retrieving information about legal * data values. The format of such trees is plug-in dependent, but * plug-ins may choose to support a plug-in neutral format described * below. A single plug-in may support multiple metadata formats, * whose names maybe determined by calling * {@code getMetadataFormatNames}. The plug-in may also support * a single special format, referred to as the "native" format, which * is designed to encode its metadata losslessly. This format will * typically be designed specifically to work with a specific file * format, so that images may be loaded and saved in the same format * with no loss of metadata, but may be less useful for transferring * metadata between an {@code ImageReader} and an * {@code ImageWriter} for different image formats. To convert * between two native formats as losslessly as the image file formats * will allow, an {@code ImageTranscoder} object must be used. * * @see javax.imageio.ImageReader#getImageMetadata * @see javax.imageio.ImageReader#getStreamMetadata * @see javax.imageio.ImageReader#readAll * @see javax.imageio.ImageWriter#getDefaultStreamMetadata * @see javax.imageio.ImageWriter#getDefaultImageMetadata * @see javax.imageio.ImageWriter#write * @see javax.imageio.ImageWriter#convertImageMetadata * @see javax.imageio.ImageWriter#convertStreamMetadata * @see javax.imageio.IIOImage * @see javax.imageio.ImageTranscoder * */ public abstract class IIOMetadata { /** * A boolean indicating whether the concrete subclass supports the * standard metadata format, set via the constructor. */ protected boolean standardFormatSupported; /** * The name of the native metadata format for this object, * initialized to {@code null} and set via the constructor. */ protected String nativeMetadataFormatName = null; /** * The name of the class implementing {@code IIOMetadataFormat} * and representing the native metadata format, initialized to * {@code null} and set via the constructor. */ protected String nativeMetadataFormatClassName = null; /** * An array of names of formats, other than the standard and * native formats, that are supported by this plug-in, * initialized to {@code null} and set via the constructor. */ protected String[] extraMetadataFormatNames = null; /** * An array of names of classes implementing {@code IIOMetadataFormat} * and representing the metadata formats, other than the standard and * native formats, that are supported by this plug-in, * initialized to {@code null} and set via the constructor. */ protected String[] extraMetadataFormatClassNames = null; /** * An {@code IIOMetadataController} that is suggested for use * as the controller for this {@code IIOMetadata} object. It * may be retrieved via {@code getDefaultController}. To * install the default controller, call * {@code setController(getDefaultController())}. This * instance variable should be set by subclasses that choose to * provide their own default controller, usually a GUI, for * setting parameters. * * @see IIOMetadataController * @see #getDefaultController */ protected IIOMetadataController defaultController = null; /** * The {@code IIOMetadataController} that will be * used to provide settings for this {@code IIOMetadata} * object when the {@code activateController} method * is called. This value overrides any default controller, * even when {@code null}. * * @see IIOMetadataController * @see #setController(IIOMetadataController) * @see #hasController() * @see #activateController() */ protected IIOMetadataController controller = null; /** * Constructs an empty {@code IIOMetadata} object. The * subclass is responsible for supplying values for all protected * instance variables that will allow any non-overridden default * implementations of methods to satisfy their contracts. For example, * {@code extraMetadataFormatNames} should not have length 0. */ protected IIOMetadata() { } /** * Constructs an {@code IIOMetadata} object with the given * format names and format class names, as well as a boolean * indicating whether the standard format is supported. * * <p> This constructor does not attempt to check the class names * for validity. Invalid class names may cause exceptions in * subsequent calls to {@code getMetadataFormat}. * * @param standardMetadataFormatSupported {@code true} if * this object can return or accept a DOM tree using the standard * metadata format. * @param nativeMetadataFormatName the name of the native metadata * format, as a {@code String}, or {@code null} if there * is no native format. * @param nativeMetadataFormatClassName the name of the class of * the native metadata format, or {@code null} if there is * no native format. * @param extraMetadataFormatNames an array of {@code String}s * indicating additional formats supported by this object, or * {@code null} if there are none. * @param extraMetadataFormatClassNames an array of {@code String}s * indicating the class names of any additional formats supported by * this object, or {@code null} if there are none. * * @exception IllegalArgumentException if * {@code extraMetadataFormatNames} has length 0. * @exception IllegalArgumentException if * {@code extraMetadataFormatNames} and * {@code extraMetadataFormatClassNames} are neither both * {@code null}, nor of the same length. */ protected IIOMetadata(boolean standardMetadataFormatSupported, String nativeMetadataFormatName, String nativeMetadataFormatClassName, String[] extraMetadataFormatNames, String[] extraMetadataFormatClassNames) { this.standardFormatSupported = standardMetadataFormatSupported; this.nativeMetadataFormatName = nativeMetadataFormatName; this.nativeMetadataFormatClassName = nativeMetadataFormatClassName; if (extraMetadataFormatNames != null) { if (extraMetadataFormatNames.length == 0) { throw new IllegalArgumentException("extraMetadataFormatNames.length == 0!"); } if (extraMetadataFormatClassNames == null) { throw new IllegalArgumentException( "extraMetadataFormatNames != null && extraMetadataFormatClassNames == null!"); } if (extraMetadataFormatClassNames.length != extraMetadataFormatNames.length) { throw new IllegalArgumentException( "extraMetadataFormatClassNames.length != extraMetadataFormatNames.length!"); } this.extraMetadataFormatNames = extraMetadataFormatNames.clone(); this.extraMetadataFormatClassNames = extraMetadataFormatClassNames.clone(); } else { if (extraMetadataFormatClassNames != null) { throw new IllegalArgumentException( "extraMetadataFormatNames == null && extraMetadataFormatClassNames != null!"); } } } /** * Returns {@code true} if the standard metadata format is * supported by {@code getMetadataFormat}, * {@code getAsTree}, {@code setFromTree}, and * {@code mergeTree}. * * <p> The default implementation returns the value of the * {@code standardFormatSupported} instance variable. * * @return {@code true} if the standard metadata format * is supported. * * @see #getAsTree * @see #setFromTree * @see #mergeTree * @see #getMetadataFormat */ public boolean isStandardMetadataFormatSupported() { return standardFormatSupported; } /** * Returns {@code true} if this object does not support the * {@code mergeTree}, {@code setFromTree}, and * {@code reset} methods. * * @return true if this {@code IIOMetadata} object cannot be * modified. */ public abstract boolean isReadOnly(); /** * Returns the name of the "native" metadata format for this * plug-in, which typically allows for lossless encoding and * transmission of the metadata stored in the format handled by * this plug-in. If no such format is supported, * {@code null} will be returned. * * <p> The structure and contents of the "native" metadata format * are defined by the plug-in that created this * {@code IIOMetadata} object. Plug-ins for simple formats * will usually create a dummy node for the root, and then a * series of child nodes representing individual tags, chunks, or * keyword/value pairs. A plug-in may choose whether or not to * document its native format. * * <p> The default implementation returns the value of the * {@code nativeMetadataFormatName} instance variable. * * @return the name of the native format, or {@code null}. * * @see #getExtraMetadataFormatNames * @see #getMetadataFormatNames */ public String getNativeMetadataFormatName() { return nativeMetadataFormatName; } /** * Returns an array of {@code String}s containing the names * of additional metadata formats, other than the native and standard * formats, recognized by this plug-in's * {@code getAsTree}, {@code setFromTree}, and * {@code mergeTree} methods. If there are no such additional * formats, {@code null} is returned. * * <p> The default implementation returns a clone of the * {@code extraMetadataFormatNames} instance variable. * * @return an array of {@code String}s with length at least * 1, or {@code null}. * * @see #getAsTree * @see #setFromTree * @see #mergeTree * @see #getNativeMetadataFormatName * @see #getMetadataFormatNames */ public String[] getExtraMetadataFormatNames() { if (extraMetadataFormatNames == null) { return null; } return extraMetadataFormatNames.clone(); } /** * Returns an array of {@code String}s containing the names * of all metadata formats, including the native and standard * formats, recognized by this plug-in's {@code getAsTree}, * {@code setFromTree}, and {@code mergeTree} methods. * If there are no such formats, {@code null} is returned. * * <p> The default implementation calls * {@code getNativeMetadataFormatName}, * {@code isStandardMetadataFormatSupported}, and * {@code getExtraMetadataFormatNames} and returns the * combined results. * * @return an array of {@code String}s. * * @see #getNativeMetadataFormatName * @see #isStandardMetadataFormatSupported * @see #getExtraMetadataFormatNames */ public String[] getMetadataFormatNames() { String nativeName = getNativeMetadataFormatName(); String standardName = isStandardMetadataFormatSupported() ? IIOMetadataFormatImpl.standardMetadataFormatName : null; String[] extraNames = getExtraMetadataFormatNames(); int numFormats = 0; if (nativeName != null) { ++numFormats; } if (standardName != null) { ++numFormats; } if (extraNames != null) { numFormats += extraNames.length; } if (numFormats == 0) { return null; } String[] formats = new String[numFormats]; int index = 0; if (nativeName != null) { formats[index++] = nativeName; } if (standardName != null) { formats[index++] = standardName; } if (extraNames != null) { for (int i = 0; i < extraNames.length; i++) { formats[index++] = extraNames[i]; } } return formats; } /** * Returns an {@code IIOMetadataFormat} object describing the * given metadata format, or {@code null} if no description * is available. The supplied name must be one of those returned * by {@code getMetadataFormatNames} (<i>i.e.</i>, either the * native format name, the standard format name, or one of those * returned by {@code getExtraMetadataFormatNames}). * * <p> The default implementation checks the name against the * global standard metadata format name, and returns that format * if it is supported. Otherwise, it checks against the native * format names followed by any additional format names. If a * match is found, it retrieves the name of the * {@code IIOMetadataFormat} class from * {@code nativeMetadataFormatClassName} or * {@code extraMetadataFormatClassNames} as appropriate, and * constructs an instance of that class using its * {@code getInstance} method. * * @param formatName the desired metadata format. * * @return an {@code IIOMetadataFormat} object. * * @exception IllegalArgumentException if {@code formatName} * is {@code null} or is not one of the names recognized by * the plug-in. * @exception IllegalStateException if the class corresponding to * the format name cannot be loaded. */ public IIOMetadataFormat getMetadataFormat(String formatName) { if (formatName == null) { throw new IllegalArgumentException("formatName == null!"); } if (standardFormatSupported && formatName.equals(IIOMetadataFormatImpl.standardMetadataFormatName)) { return IIOMetadataFormatImpl.getStandardFormatInstance(); } String formatClassName = null; if (formatName.equals(nativeMetadataFormatName)) { formatClassName = nativeMetadataFormatClassName; } else if (extraMetadataFormatNames != null) { for (int i = 0; i < extraMetadataFormatNames.length; i++) { if (formatName.equals(extraMetadataFormatNames[i])) { formatClassName = extraMetadataFormatClassNames[i]; break; // out of for } } } if (formatClassName == null) { throw new IllegalArgumentException("Unsupported format name"); } try { final String className = formatClassName; // Try to load from the module of the IIOMetadata implementation // for this plugin since the IIOMetadataImpl is part of the plugin PrivilegedAction<Class<?>> pa = () -> { return getMetadataFormatClass(className); }; Class<?> cls = AccessController.doPrivileged(pa); Method meth = cls.getMethod("getInstance"); return (IIOMetadataFormat) meth.invoke(null); } catch (Exception e) { RuntimeException ex = new IllegalStateException("Can't obtain format"); ex.initCause(e); throw ex; } } // If updating this method also see the same in ImageReaderWriterSpi.java private Class<?> getMetadataFormatClass(String formatClassName) { Module thisModule = IIOMetadata.class.getModule(); Module targetModule = this.getClass().getModule(); Class<?> c = null; try { ClassLoader cl = this.getClass().getClassLoader(); c = Class.forName(formatClassName, false, cl); if (!IIOMetadataFormat.class.isAssignableFrom(c)) { return null; } } catch (ClassNotFoundException e) { } if (thisModule.equals(targetModule) || c == null) { return c; } if (targetModule.isNamed()) { int i = formatClassName.lastIndexOf("."); String pn = i > 0 ? formatClassName.substring(0, i) : ""; if (!targetModule.isExported(pn, thisModule)) { throw new IllegalStateException( "Class " + formatClassName + " in named module must be exported to java.desktop module."); } } return c; } /** * Returns an XML DOM {@code Node} object that represents the * root of a tree of metadata contained within this object * according to the conventions defined by a given metadata * format. * * <p> The names of the available metadata formats may be queried * using the {@code getMetadataFormatNames} method. * * @param formatName the desired metadata format. * * @return an XML DOM {@code Node} object forming the * root of a tree. * * @exception IllegalArgumentException if {@code formatName} * is {@code null} or is not one of the names returned by * {@code getMetadataFormatNames}. * * @see #getMetadataFormatNames * @see #setFromTree * @see #mergeTree */ public abstract Node getAsTree(String formatName); /** * Alters the internal state of this {@code IIOMetadata} * object from a tree of XML DOM {@code Node}s whose syntax * is defined by the given metadata format. The previous state is * altered only as necessary to accommodate the nodes that are * present in the given tree. If the tree structure or contents * are invalid, an {@code IIOInvalidTreeException} will be * thrown. * * <p> As the semantics of how a tree or subtree may be merged with * another tree are completely format-specific, plug-in authors may * implement this method in whatever manner is most appropriate for * the format, including simply replacing all existing state with the * contents of the given tree. * * @param formatName the desired metadata format. * @param root an XML DOM {@code Node} object forming the * root of a tree. * * @exception IllegalStateException if this object is read-only. * @exception IllegalArgumentException if {@code formatName} * is {@code null} or is not one of the names returned by * {@code getMetadataFormatNames}. * @exception IllegalArgumentException if {@code root} is * {@code null}. * @exception IIOInvalidTreeException if the tree cannot be parsed * successfully using the rules of the given format. * * @see #getMetadataFormatNames * @see #getAsTree * @see #setFromTree */ public abstract void mergeTree(String formatName, Node root) throws IIOInvalidTreeException; /** * Returns an {@code IIOMetadataNode} representing the chroma * information of the standard {@code javax_imageio_1.0} * metadata format, or {@code null} if no such information is * available. This method is intended to be called by the utility * routine {@code getStandardTree}. * * <p> The default implementation returns {@code null}. * * <p> Subclasses should override this method to produce an * appropriate subtree if they wish to support the standard * metadata format. * * @return an {@code IIOMetadataNode}, or {@code null}. * * @see #getStandardTree */ protected IIOMetadataNode getStandardChromaNode() { return null; } /** * Returns an {@code IIOMetadataNode} representing the * compression information of the standard * {@code javax_imageio_1.0} metadata format, or * {@code null} if no such information is available. This * method is intended to be called by the utility routine * {@code getStandardTree}. * * <p> The default implementation returns {@code null}. * * <p> Subclasses should override this method to produce an * appropriate subtree if they wish to support the standard * metadata format. * * @return an {@code IIOMetadataNode}, or {@code null}. * * @see #getStandardTree */ protected IIOMetadataNode getStandardCompressionNode() { return null; } /** * Returns an {@code IIOMetadataNode} representing the data * format information of the standard * {@code javax_imageio_1.0} metadata format, or * {@code null} if no such information is available. This * method is intended to be called by the utility routine * {@code getStandardTree}. * * <p> The default implementation returns {@code null}. * * <p> Subclasses should override this method to produce an * appropriate subtree if they wish to support the standard * metadata format. * * @return an {@code IIOMetadataNode}, or {@code null}. * * @see #getStandardTree */ protected IIOMetadataNode getStandardDataNode() { return null; } /** * Returns an {@code IIOMetadataNode} representing the * dimension information of the standard * {@code javax_imageio_1.0} metadata format, or * {@code null} if no such information is available. This * method is intended to be called by the utility routine * {@code getStandardTree}. * * <p> The default implementation returns {@code null}. * * <p> Subclasses should override this method to produce an * appropriate subtree if they wish to support the standard * metadata format. * * @return an {@code IIOMetadataNode}, or {@code null}. * * @see #getStandardTree */ protected IIOMetadataNode getStandardDimensionNode() { return null; } /** * Returns an {@code IIOMetadataNode} representing the document * information of the standard {@code javax_imageio_1.0} * metadata format, or {@code null} if no such information is * available. This method is intended to be called by the utility * routine {@code getStandardTree}. * * <p> The default implementation returns {@code null}. * * <p> Subclasses should override this method to produce an * appropriate subtree if they wish to support the standard * metadata format. * * @return an {@code IIOMetadataNode}, or {@code null}. * * @see #getStandardTree */ protected IIOMetadataNode getStandardDocumentNode() { return null; } /** * Returns an {@code IIOMetadataNode} representing the textual * information of the standard {@code javax_imageio_1.0} * metadata format, or {@code null} if no such information is * available. This method is intended to be called by the utility * routine {@code getStandardTree}. * * <p> The default implementation returns {@code null}. * * <p> Subclasses should override this method to produce an * appropriate subtree if they wish to support the standard * metadata format. * * @return an {@code IIOMetadataNode}, or {@code null}. * * @see #getStandardTree */ protected IIOMetadataNode getStandardTextNode() { return null; } /** * Returns an {@code IIOMetadataNode} representing the tiling * information of the standard {@code javax_imageio_1.0} * metadata format, or {@code null} if no such information is * available. This method is intended to be called by the utility * routine {@code getStandardTree}. * * <p> The default implementation returns {@code null}. * * <p> Subclasses should override this method to produce an * appropriate subtree if they wish to support the standard * metadata format. * * @return an {@code IIOMetadataNode}, or {@code null}. * * @see #getStandardTree */ protected IIOMetadataNode getStandardTileNode() { return null; } /** * Returns an {@code IIOMetadataNode} representing the * transparency information of the standard * {@code javax_imageio_1.0} metadata format, or * {@code null} if no such information is available. This * method is intended to be called by the utility routine * {@code getStandardTree}. * * <p> The default implementation returns {@code null}. * * <p> Subclasses should override this method to produce an * appropriate subtree if they wish to support the standard * metadata format. * * @return an {@code IIOMetadataNode}, or {@code null}. */ protected IIOMetadataNode getStandardTransparencyNode() { return null; } /** * Appends a new node to an existing node, if the new node is * non-{@code null}. */ private void append(IIOMetadataNode root, IIOMetadataNode node) { if (node != null) { root.appendChild(node); } } /** * A utility method to return a tree of * {@code IIOMetadataNode}s representing the metadata * contained within this object according to the conventions of * the standard {@code javax_imageio_1.0} metadata format. * * <p> This method calls the various {@code getStandard*Node} * methods to supply each of the subtrees rooted at the children * of the root node. If any of those methods returns * {@code null}, the corresponding subtree will be omitted. * If all of them return {@code null}, a tree consisting of a * single root node will be returned. * * @return an {@code IIOMetadataNode} representing the root * of a metadata tree in the {@code javax_imageio_1.0} * format. * * @see #getStandardChromaNode * @see #getStandardCompressionNode * @see #getStandardDataNode * @see #getStandardDimensionNode * @see #getStandardDocumentNode * @see #getStandardTextNode * @see #getStandardTileNode * @see #getStandardTransparencyNode */ protected final IIOMetadataNode getStandardTree() { IIOMetadataNode root = new IIOMetadataNode(IIOMetadataFormatImpl.standardMetadataFormatName); append(root, getStandardChromaNode()); append(root, getStandardCompressionNode()); append(root, getStandardDataNode()); append(root, getStandardDimensionNode()); append(root, getStandardDocumentNode()); append(root, getStandardTextNode()); append(root, getStandardTileNode()); append(root, getStandardTransparencyNode()); return root; } /** * Sets the internal state of this {@code IIOMetadata} object * from a tree of XML DOM {@code Node}s whose syntax is * defined by the given metadata format. The previous state is * discarded. If the tree's structure or contents are invalid, an * {@code IIOInvalidTreeException} will be thrown. * * <p> The default implementation calls {@code reset} * followed by {@code mergeTree(formatName, root)}. * * @param formatName the desired metadata format. * @param root an XML DOM {@code Node} object forming the * root of a tree. * * @exception IllegalStateException if this object is read-only. * @exception IllegalArgumentException if {@code formatName} * is {@code null} or is not one of the names returned by * {@code getMetadataFormatNames}. * @exception IllegalArgumentException if {@code root} is * {@code null}. * @exception IIOInvalidTreeException if the tree cannot be parsed * successfully using the rules of the given format. * * @see #getMetadataFormatNames * @see #getAsTree * @see #mergeTree */ public void setFromTree(String formatName, Node root) throws IIOInvalidTreeException { reset(); mergeTree(formatName, root); } /** * Resets all the data stored in this object to default values, * usually to the state this object was in immediately after * construction, though the precise semantics are plug-in specific. * Note that there are many possible default values, depending on * how the object was created. * * @exception IllegalStateException if this object is read-only. * * @see javax.imageio.ImageReader#getStreamMetadata * @see javax.imageio.ImageReader#getImageMetadata * @see javax.imageio.ImageWriter#getDefaultStreamMetadata * @see javax.imageio.ImageWriter#getDefaultImageMetadata */ public abstract void reset(); /** * Sets the {@code IIOMetadataController} to be used * to provide settings for this {@code IIOMetadata} * object when the {@code activateController} method * is called, overriding any default controller. If the * argument is {@code null}, no controller will be * used, including any default. To restore the default, use * {@code setController(getDefaultController())}. * * <p> The default implementation sets the {@code controller} * instance variable to the supplied value. * * @param controller An appropriate * {@code IIOMetadataController}, or {@code null}. * * @see IIOMetadataController * @see #getController * @see #getDefaultController * @see #hasController * @see #activateController() */ public void setController(IIOMetadataController controller) { this.controller = controller; } /** * Returns whatever {@code IIOMetadataController} is currently * installed. This could be the default if there is one, * {@code null}, or the argument of the most recent call * to {@code setController}. * * <p> The default implementation returns the value of the * {@code controller} instance variable. * * @return the currently installed * {@code IIOMetadataController}, or {@code null}. * * @see IIOMetadataController * @see #setController * @see #getDefaultController * @see #hasController * @see #activateController() */ public IIOMetadataController getController() { return controller; } /** * Returns the default {@code IIOMetadataController}, if there * is one, regardless of the currently installed controller. If * there is no default controller, returns {@code null}. * * <p> The default implementation returns the value of the * {@code defaultController} instance variable. * * @return the default {@code IIOMetadataController}, or * {@code null}. * * @see IIOMetadataController * @see #setController(IIOMetadataController) * @see #getController * @see #hasController * @see #activateController() */ public IIOMetadataController getDefaultController() { return defaultController; } /** * Returns {@code true} if there is a controller installed * for this {@code IIOMetadata} object. * * <p> The default implementation returns {@code true} if the * {@code getController} method returns a * non-{@code null} value. * * @return {@code true} if a controller is installed. * * @see IIOMetadataController * @see #setController(IIOMetadataController) * @see #getController * @see #getDefaultController * @see #activateController() */ public boolean hasController() { return (getController() != null); } /** * Activates the installed {@code IIOMetadataController} for * this {@code IIOMetadata} object and returns the resulting * value. When this method returns {@code true}, all values for this * {@code IIOMetadata} object will be ready for the next write * operation. If {@code false} is * returned, no settings in this object will have been disturbed * (<i>i.e.</i>, the user canceled the operation). * * <p> Ordinarily, the controller will be a GUI providing a user * interface for a subclass of {@code IIOMetadata} for a * particular plug-in. Controllers need not be GUIs, however. * * <p> The default implementation calls {@code getController} * and the calls {@code activate} on the returned object if * {@code hasController} returns {@code true}. * * @return {@code true} if the controller completed normally. * * @exception IllegalStateException if there is no controller * currently installed. * * @see IIOMetadataController * @see #setController(IIOMetadataController) * @see #getController * @see #getDefaultController * @see #hasController */ public boolean activateController() { if (!hasController()) { throw new IllegalStateException("hasController() == false!"); } return getController().activate(this); } }