Java tutorial
/* * Copyright (c) 1999, 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.spi; import java.io.IOException; import javax.imageio.ImageReader; import javax.imageio.stream.ImageInputStream; /** * The service provider interface (SPI) for {@code ImageReader}s. * For more information on service provider classes, see the class comment * for the {@code IIORegistry} class. * * <p> Each {@code ImageReaderSpi} provides several types of information * about the {@code ImageReader} class with which it is associated. * * <p> The name of the vendor who defined the SPI class and a * brief description of the class are available via the * {@code getVendorName}, {@code getDescription}, * and {@code getVersion} methods. * These methods may be internationalized to provide locale-specific * output. These methods are intended mainly to provide short, * human-readable information that might be used to organize a pop-up * menu or other list. * * <p> Lists of format names, file suffixes, and MIME types associated * with the service may be obtained by means of the * {@code getFormatNames}, {@code getFileSuffixes}, and * {@code getMIMETypes} methods. These methods may be used to * identify candidate {@code ImageReader}s for decoding a * particular file or stream based on manual format selection, file * naming, or MIME associations (for example, when accessing a file * over HTTP or as an email attachment). * * <p> A more reliable way to determine which {@code ImageReader}s * are likely to be able to parse a particular data stream is provided * by the {@code canDecodeInput} method. This methods allows the * service provider to inspect the actual stream contents. * * <p> Finally, an instance of the {@code ImageReader} class * associated with this service provider may be obtained by calling * the {@code createReaderInstance} method. Any heavyweight * initialization, such as the loading of native libraries or creation * of large tables, should be deferred at least until the first * invocation of this method. * * @see IIORegistry * @see javax.imageio.ImageReader * */ public abstract class ImageReaderSpi extends ImageReaderWriterSpi { /** * A single-element array, initially containing * {@code ImageInputStream.class}, to be returned from * {@code getInputTypes}. * @deprecated Instead of using this field, directly create * the equivalent array {@code { ImageInputStream.class }}. */ @Deprecated public static final Class<?>[] STANDARD_INPUT_TYPE = { ImageInputStream.class }; /** * An array of {@code Class} objects to be returned from * {@code getInputTypes}, initially {@code null}. */ protected Class<?>[] inputTypes = null; /** * An array of strings to be returned from * {@code getImageWriterSpiNames}, initially * {@code null}. */ protected String[] writerSpiNames = null; /** * The {@code Class} of the reader, initially * {@code null}. */ private Class<?> readerClass = null; /** * Constructs a blank {@code ImageReaderSpi}. It is up to * the subclass to initialize instance variables and/or override * method implementations in order to provide working versions of * all methods. */ protected ImageReaderSpi() { } /** * Constructs an {@code ImageReaderSpi} with a given * set of values. * * @param vendorName the vendor name, as a non-{@code null} * {@code String}. * @param version a version identifier, as a non-{@code null} * {@code String}. * @param names a non-{@code null} array of * {@code String}s indicating the format names. At least one * entry must be present. * @param suffixes an array of {@code String}s indicating the * common file suffixes. If no suffixes are defined, * {@code null} should be supplied. An array of length 0 * will be normalized to {@code null}. * @param MIMETypes an array of {@code String}s indicating * the format's MIME types. If no MIME types are defined, * {@code null} should be supplied. An array of length 0 * will be normalized to {@code null}. * @param readerClassName the fully-qualified name of the * associated {@code ImageReader} class, as a * non-{@code null String}. * @param inputTypes a non-{@code null} array of * {@code Class} objects of length at least 1 indicating the * legal input types. * @param writerSpiNames an array {@code String}s naming the * classes of all associated {@code ImageWriter}s, or * {@code null}. An array of length 0 is normalized to * {@code null}. * @param supportsStandardStreamMetadataFormat a * {@code boolean} that indicates whether a stream metadata * object can use trees described by the standard metadata format. * @param nativeStreamMetadataFormatName a * {@code String}, or {@code null}, to be returned from * {@code getNativeStreamMetadataFormatName}. * @param nativeStreamMetadataFormatClassName a * {@code String}, or {@code null}, to be used to instantiate * a metadata format object to be returned from * {@code getNativeStreamMetadataFormat}. * @param extraStreamMetadataFormatNames an array of * {@code String}s, or {@code null}, to be returned from * {@code getExtraStreamMetadataFormatNames}. An array of length * 0 is normalized to {@code null}. * @param extraStreamMetadataFormatClassNames an array of * {@code String}s, or {@code null}, to be used to instantiate * a metadata format object to be returned from * {@code getStreamMetadataFormat}. An array of length * 0 is normalized to {@code null}. * @param supportsStandardImageMetadataFormat a * {@code boolean} that indicates whether an image metadata * object can use trees described by the standard metadata format. * @param nativeImageMetadataFormatName a * {@code String}, or {@code null}, to be returned from * {@code getNativeImageMetadataFormatName}. * @param nativeImageMetadataFormatClassName a * {@code String}, or {@code null}, to be used to instantiate * a metadata format object to be returned from * {@code getNativeImageMetadataFormat}. * @param extraImageMetadataFormatNames an array of * {@code String}s to be returned from * {@code getExtraImageMetadataFormatNames}. An array of length 0 * is normalized to {@code null}. * @param extraImageMetadataFormatClassNames an array of * {@code String}s, or {@code null}, to be used to instantiate * a metadata format object to be returned from * {@code getImageMetadataFormat}. An array of length * 0 is normalized to {@code null}. * * @exception IllegalArgumentException if {@code vendorName} * is {@code null}. * @exception IllegalArgumentException if {@code version} * is {@code null}. * @exception IllegalArgumentException if {@code names} * is {@code null} or has length 0. * @exception IllegalArgumentException if {@code readerClassName} * is {@code null}. * @exception IllegalArgumentException if {@code inputTypes} * is {@code null} or has length 0. */ public ImageReaderSpi(String vendorName, String version, String[] names, String[] suffixes, String[] MIMETypes, String readerClassName, Class<?>[] inputTypes, String[] writerSpiNames, boolean supportsStandardStreamMetadataFormat, String nativeStreamMetadataFormatName, String nativeStreamMetadataFormatClassName, String[] extraStreamMetadataFormatNames, String[] extraStreamMetadataFormatClassNames, boolean supportsStandardImageMetadataFormat, String nativeImageMetadataFormatName, String nativeImageMetadataFormatClassName, String[] extraImageMetadataFormatNames, String[] extraImageMetadataFormatClassNames) { super(vendorName, version, names, suffixes, MIMETypes, readerClassName, supportsStandardStreamMetadataFormat, nativeStreamMetadataFormatName, nativeStreamMetadataFormatClassName, extraStreamMetadataFormatNames, extraStreamMetadataFormatClassNames, supportsStandardImageMetadataFormat, nativeImageMetadataFormatName, nativeImageMetadataFormatClassName, extraImageMetadataFormatNames, extraImageMetadataFormatClassNames); if (inputTypes == null) { throw new IllegalArgumentException("inputTypes == null!"); } if (inputTypes.length == 0) { throw new IllegalArgumentException("inputTypes.length == 0!"); } this.inputTypes = (inputTypes == STANDARD_INPUT_TYPE) ? new Class<?>[] { ImageInputStream.class } : inputTypes.clone(); // If length == 0, leave it null if (writerSpiNames != null && writerSpiNames.length > 0) { this.writerSpiNames = writerSpiNames.clone(); } } /** * Returns an array of {@code Class} objects indicating what * types of objects may be used as arguments to the reader's * {@code setInput} method. * * <p> For most readers, which only accept input from an * {@code ImageInputStream}, a single-element array * containing {@code ImageInputStream.class} should be * returned. * * @return a non-{@code null} array of * {@code Class} objects of length at least 1. */ public Class<?>[] getInputTypes() { return inputTypes.clone(); } /** * Returns {@code true} if the supplied source object appears * to be of the format supported by this reader. Returning * {@code true} from this method does not guarantee that * reading will succeed, only that there appears to be a * reasonable chance of success based on a brief inspection of the * stream contents. If the source is an * {@code ImageInputStream}, implementations will commonly * check the first several bytes of the stream for a "magic * number" associated with the format. Once actual reading has * commenced, the reader may still indicate failure at any time * prior to the completion of decoding. * * <p> It is important that the state of the object not be * disturbed in order that other {@code ImageReaderSpi}s can * properly determine whether they are able to decode the object. * In particular, if the source is an * {@code ImageInputStream}, a * {@code mark}/{@code reset} pair should be used to * preserve the stream position. * * <p> Formats such as "raw," which can potentially attempt * to read nearly any stream, should return {@code false} * in order to avoid being invoked in preference to a closer * match. * * <p> If {@code source} is not an instance of one of the * classes returned by {@code getInputTypes}, the method * should simply return {@code false}. * * @param source the object (typically an * {@code ImageInputStream}) to be decoded. * * @return {@code true} if it is likely that this stream can * be decoded. * * @exception IllegalArgumentException if {@code source} is * {@code null}. * @exception IOException if an I/O error occurs while reading the * stream. */ public abstract boolean canDecodeInput(Object source) throws IOException; /** * Returns an instance of the {@code ImageReader} * implementation associated with this service provider. * The returned object will initially be in an initial state * as if its {@code reset} method had been called. * * <p> The default implementation simply returns * {@code createReaderInstance(null)}. * * @return an {@code ImageReader} instance. * * @exception IOException if an error occurs during loading, * or initialization of the reader class, or during instantiation * or initialization of the reader object. */ public ImageReader createReaderInstance() throws IOException { return createReaderInstance(null); } /** * Returns an instance of the {@code ImageReader} * implementation associated with this service provider. * The returned object will initially be in an initial state * as if its {@code reset} method had been called. * * <p> An {@code Object} may be supplied to the plug-in at * construction time. The nature of the object is entirely * plug-in specific. * * <p> Typically, a plug-in will implement this method using code * such as {@code return new MyImageReader(this)}. * * @param extension a plug-in specific extension object, which may * be {@code null}. * * @return an {@code ImageReader} instance. * * @exception IOException if the attempt to instantiate * the reader fails. * @exception IllegalArgumentException if the * {@code ImageReader}'s constructor throws an * {@code IllegalArgumentException} to indicate that the * extension object is unsuitable. */ public abstract ImageReader createReaderInstance(Object extension) throws IOException; /** * Returns {@code true} if the {@code ImageReader} object * passed in is an instance of the {@code ImageReader} * associated with this service provider. * * <p> The default implementation compares the fully-qualified * class name of the {@code reader} argument with the class * name passed into the constructor. This method may be overridden * if more sophisticated checking is required. * * @param reader an {@code ImageReader} instance. * * @return {@code true} if {@code reader} is recognized. * * @exception IllegalArgumentException if {@code reader} is * {@code null}. */ public boolean isOwnReader(ImageReader reader) { if (reader == null) { throw new IllegalArgumentException("reader == null!"); } String name = reader.getClass().getName(); return name.equals(pluginClassName); } /** * Returns an array of {@code String}s containing the fully * qualified names of all the {@code ImageWriterSpi} classes * that can understand the internal metadata representation used * by the {@code ImageReader} associated with this service * provider, or {@code null} if there are no such * {@code ImageWriter}s specified. If a * non-{@code null} value is returned, it must have non-zero * length. * * <p> The first item in the array must be the name of the service * provider for the "preferred" writer, as it will be used to * instantiate the {@code ImageWriter} returned by * {@code ImageIO.getImageWriter(ImageReader)}. * * <p> This mechanism may be used to obtain * {@code ImageWriters} that will understand the internal * structure of non-pixel meta-data (see * {@code IIOTreeInfo}) generated by an * {@code ImageReader}. By obtaining this data from the * {@code ImageReader} and passing it on to one of the * {@code ImageWriters} obtained with this method, a client * program can read an image, modify it in some way, and write it * back out while preserving all meta-data, without having to * understand anything about the internal structure of the * meta-data, or even about the image format. * * @return an array of {@code String}s of length at least 1 * containing names of {@code ImageWriterSpi}, or * {@code null}. * * @see javax.imageio.ImageIO#getImageWriter(ImageReader) */ public String[] getImageWriterSpiNames() { return writerSpiNames == null ? null : writerSpiNames.clone(); } }