1 /*
   2  * Copyright (c) 2000, 2004, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package javax.imageio.spi;
  27 
  28 import java.io.File;
  29 import java.io.IOException;
  30 import javax.imageio.stream.ImageInputStream;
  31 
  32 /**
  33  * The service provider interface (SPI) for
  34  * {@code ImageInputStream}s.  For more information on service
  35  * provider interfaces, see the class comment for the
  36  * {@code IIORegistry} class.
  37  *
  38  * <p> This interface allows arbitrary objects to be "wrapped" by
  39  * instances of {@code ImageInputStream}.  For example,
  40  * a particular {@code ImageInputStreamSpi} might allow
  41  * a generic {@code InputStream} to be used as an input source;
  42  * another might take input from a {@code URL}.
  43  *
  44  * <p> By treating the creation of {@code ImageInputStream}s as a
  45  * pluggable service, it becomes possible to handle future input
  46  * sources without changing the API.  Also, high-performance
  47  * implementations of {@code ImageInputStream} (for example,
  48  * native implementations for a particular platform) can be installed
  49  * and used transparently by applications.
  50  *
  51  * @see IIORegistry
  52  * @see javax.imageio.stream.ImageInputStream
  53  *
  54  */
  55 public abstract class ImageInputStreamSpi extends IIOServiceProvider {
  56 
  57     /**
  58      * A {@code Class} object indicating the legal object type
  59      * for use by the {@code createInputStreamInstance} method.
  60      */
  61     protected Class<?> inputClass;
  62 
  63     /**
  64      * Constructs a blank {@code ImageInputStreamSpi}.  It is up
  65      * to the subclass to initialize instance variables and/or
  66      * override method implementations in order to provide working
  67      * versions of all methods.
  68      */
  69     protected ImageInputStreamSpi() {
  70     }
  71 
  72     /**
  73      * Constructs an {@code ImageInputStreamSpi} with a given set
  74      * of values.
  75      *
  76      * @param vendorName the vendor name.
  77      * @param version a version identifier.
  78      * @param inputClass a {@code Class} object indicating the
  79      * legal object type for use by the
  80      * {@code createInputStreamInstance} method.
  81      *
  82      * @exception IllegalArgumentException if {@code vendorName}
  83      * is {@code null}.
  84      * @exception IllegalArgumentException if {@code version}
  85      * is {@code null}.
  86      */
  87     public ImageInputStreamSpi(String vendorName,
  88                                String version,
  89                                Class<?> inputClass) {
  90         super(vendorName, version);
  91         this.inputClass = inputClass;
  92     }
  93 
  94     /**
  95      * Returns a {@code Class} object representing the class or
  96      * interface type that must be implemented by an input source in
  97      * order to be "wrapped" in an {@code ImageInputStream} via
  98      * the {@code createInputStreamInstance} method.
  99      *
 100      * <p> Typical return values might include
 101      * {@code InputStream.class} or {@code URL.class}, but
 102      * any class may be used.
 103      *
 104      * @return a {@code Class} variable.
 105      *
 106      * @see #createInputStreamInstance(Object, boolean, File)
 107      */
 108     public Class<?> getInputClass() {
 109         return inputClass;
 110     }
 111 
 112     /**
 113      * Returns {@code true} if the {@code ImageInputStream}
 114      * implementation associated with this service provider can
 115      * optionally make use of a cache file for improved performance
 116      * and/or memory footrprint.  If {@code false}, the value of
 117      * the {@code useCache} argument to
 118      * {@code createInputStreamInstance} will be ignored.
 119      *
 120      * <p> The default implementation returns {@code false}.
 121      *
 122      * @return {@code true} if a cache file can be used by the
 123      * input streams created by this service provider.
 124      */
 125     public boolean canUseCacheFile() {
 126         return false;
 127     }
 128 
 129     /**
 130      * Returns {@code true} if the {@code ImageInputStream}
 131      * implementation associated with this service provider requires
 132      * the use of a cache {@code File}.  If {@code true},
 133      * the value of the {@code useCache} argument to
 134      * {@code createInputStreamInstance} will be ignored.
 135      *
 136      * <p> The default implementation returns {@code false}.
 137      *
 138      * @return {@code true} if a cache file is needed by the
 139      * input streams created by this service provider.
 140      */
 141     public boolean needsCacheFile() {
 142         return false;
 143     }
 144 
 145     /**
 146      * Returns an instance of the {@code ImageInputStream}
 147      * implementation associated with this service provider.  If the
 148      * use of a cache file is optional, the {@code useCache}
 149      * parameter will be consulted.  Where a cache is required, or
 150      * not applicable, the value of {@code useCache} will be ignored.
 151      *
 152      * @param input an object of the class type returned by
 153      * {@code getInputClass}.
 154      * @param useCache a {@code boolean} indicating whether a
 155      * cache file should be used, in cases where it is optional.
 156      * @param cacheDir a {@code File} indicating where the
 157      * cache file should be created, or {@code null} to use the
 158      * system directory.
 159      *
 160      * @return an {@code ImageInputStream} instance.
 161      *
 162      * @exception IllegalArgumentException if {@code input} is
 163      * not an instance of the correct class or is {@code null}.
 164      * @exception IllegalArgumentException if a cache file is needed
 165      * but {@code cacheDir} is non-{@code null} and is not a
 166      * directory.
 167      * @exception IOException if a cache file is needed but cannot be
 168      * created.
 169      *
 170      * @see #getInputClass
 171      * @see #canUseCacheFile
 172      * @see #needsCacheFile
 173      */
 174     public abstract ImageInputStream
 175         createInputStreamInstance(Object input,
 176                                   boolean useCache,
 177                                   File cacheDir) throws IOException;
 178 
 179     /**
 180      * Returns an instance of the {@code ImageInputStream}
 181      * implementation associated with this service provider.  A cache
 182      * file will be created in the system-dependent default
 183      * temporary-file directory, if needed.
 184      *
 185      * @param input an object of the class type returned by
 186      * {@code getInputClass}.
 187      *
 188      * @return an {@code ImageInputStream} instance.
 189      *
 190      * @exception IllegalArgumentException if {@code input} is
 191      * not an instance of the correct class or is {@code null}.
 192      * @exception IOException if a cache file is needed but cannot be
 193      * created.
 194      *
 195      * @see #getInputClass()
 196      */
 197     public ImageInputStream createInputStreamInstance(Object input)
 198         throws IOException {
 199         return createInputStreamInstance(input, true, null);
 200     }
 201 }
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