Java example source code file (ImageInputStreamSpi.java)

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Java - Java tags/keywords

class, file, iioserviceprovider, imageinputstream, imageinputstreamspi, ioexception, string

The ImageInputStreamSpi.java Java example source code

/*
 * Copyright (c) 2000, 2004, 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.File;
import java.io.IOException;
import javax.imageio.stream.ImageInputStream;

/**
 * The service provider interface (SPI) for
 * <code>ImageInputStreams.  For more information on service
 * provider interfaces, see the class comment for the
 * <code>IIORegistry class.
 *
 * <p> This interface allows arbitrary objects to be "wrapped" by
 * instances of <code>ImageInputStream.  For example,
 * a particular <code>ImageInputStreamSpi might allow
 * a generic <code>InputStream to be used as an input source;
 * another might take input from a <code>URL.
 *
 * <p> By treating the creation of ImageInputStreams as a
 * pluggable service, it becomes possible to handle future input
 * sources without changing the API.  Also, high-performance
 * implementations of <code>ImageInputStream (for example,
 * native implementations for a particular platform) can be installed
 * and used transparently by applications.
 *
 * @see IIORegistry
 * @see javax.imageio.stream.ImageInputStream
 *
 */
public abstract class ImageInputStreamSpi extends IIOServiceProvider {

    /**
     * A <code>Class object indicating the legal object type
     * for use by the <code>createInputStreamInstance method.
     */
    protected Class<?> inputClass;

    /**
     * Constructs a blank <code>ImageInputStreamSpi.  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 ImageInputStreamSpi() {
    }

    /**
     * Constructs an <code>ImageInputStreamSpi with a given set
     * of values.
     *
     * @param vendorName the vendor name.
     * @param version a version identifier.
     * @param inputClass a <code>Class object indicating the
     * legal object type for use by the
     * <code>createInputStreamInstance method.
     *
     * @exception IllegalArgumentException if <code>vendorName
     * is <code>null.
     * @exception IllegalArgumentException if <code>version
     * is <code>null.
     */
    public ImageInputStreamSpi(String vendorName,
                               String version,
                               Class<?> inputClass) {
        super(vendorName, version);
        this.inputClass = inputClass;
    }

    /**
     * Returns a <code>Class object representing the class or
     * interface type that must be implemented by an input source in
     * order to be "wrapped" in an <code>ImageInputStream via
     * the <code>createInputStreamInstance method.
     *
     * <p> Typical return values might include
     * <code>InputStream.class or URL.class, but
     * any class may be used.
     *
     * @return a <code>Class variable.
     *
     * @see #createInputStreamInstance(Object, boolean, File)
     */
    public Class<?> getInputClass() {
        return inputClass;
    }

    /**
     * Returns <code>true if the ImageInputStream
     * implementation associated with this service provider can
     * optionally make use of a cache file for improved performance
     * and/or memory footrprint.  If <code>false, the value of
     * the <code>useCache argument to
     * <code>createInputStreamInstance will be ignored.
     *
     * <p> The default implementation returns false.
     *
     * @return <code>true if a cache file can be used by the
     * input streams created by this service provider.
     */
    public boolean canUseCacheFile() {
        return false;
    }

    /**
     * Returns <code>true if the ImageInputStream
     * implementation associated with this service provider requires
     * the use of a cache <code>File.  If true,
     * the value of the <code>useCache argument to
     * <code>createInputStreamInstance will be ignored.
     *
     * <p> The default implementation returns false.
     *
     * @return <code>true if a cache file is needed by the
     * input streams created by this service provider.
     */
    public boolean needsCacheFile() {
        return false;
    }

    /**
     * Returns an instance of the <code>ImageInputStream
     * implementation associated with this service provider.  If the
     * use of a cache file is optional, the <code>useCache
     * parameter will be consulted.  Where a cache is required, or
     * not applicable, the value of <code>useCache will be ignored.
     *
     * @param input an object of the class type returned by
     * <code>getInputClass.
     * @param useCache a <code>boolean indicating whether a
     * cache file should be used, in cases where it is optional.
     * @param cacheDir a <code>File indicating where the
     * cache file should be created, or <code>null to use the
     * system directory.
     *
     * @return an <code>ImageInputStream instance.
     *
     * @exception IllegalArgumentException if <code>input is
     * not an instance of the correct class or is <code>null.
     * @exception IllegalArgumentException if a cache file is needed
     * but <code>cacheDir is non-null and is not a
     * directory.
     * @exception IOException if a cache file is needed but cannot be
     * created.
     *
     * @see #getInputClass
     * @see #canUseCacheFile
     * @see #needsCacheFile
     */
    public abstract ImageInputStream
        createInputStreamInstance(Object input,
                                  boolean useCache,
                                  File cacheDir) throws IOException;

    /**
     * Returns an instance of the <code>ImageInputStream
     * implementation associated with this service provider.  A cache
     * file will be created in the system-dependent default
     * temporary-file directory, if needed.
     *
     * @param input an object of the class type returned by
     * <code>getInputClass.
     *
     * @return an <code>ImageInputStream instance.
     *
     * @exception IllegalArgumentException if <code>input is
     * not an instance of the correct class or is <code>null.
     * @exception IOException if a cache file is needed but cannot be
     * created.
     *
     * @see #getInputClass()
     */
    public ImageInputStream createInputStreamInstance(Object input)
        throws IOException {
        return createInputStreamInstance(input, true, null);
    }
}