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25 
26 package javax.imageio.spi;
27 
28 import java.io.File;
29 import java.io.IOException;
30 import javax.imageio.stream.ImageOutputStream;
31 
32 /**
33  * The service provider interface (SPI) for
34  * {@code ImageOutputStream}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 ImageOutputStream}.  For example, a
40  * particular {@code ImageOutputStreamSpi} might allow a generic
41  * {@code OutputStream} to be used as a destination; another
42  * might output to a {@code File} or to a device such as a serial
43  * port.
44  *
45  * <p> By treating the creation of {@code ImageOutputStream}s as
46  * a pluggable service, it becomes possible to handle future output
47  * destinations without changing the API.  Also, high-performance
48  * implementations of {@code ImageOutputStream} (for example,
49  * native implementations for a particular platform) can be installed
50  * and used transparently by applications.
51  *
52  * @see IIORegistry
53  * @see javax.imageio.stream.ImageOutputStream
54  *
55  */
56 public abstract class ImageOutputStreamSpi extends IIOServiceProvider {
57 
58     /**
59      * A {@code Class} object indicating the legal object type
60      * for use by the {@code createInputStreamInstance} method.
61      */
62     protected Class<?> outputClass;
63 
64     /**
65      * Constructs a blank {@code ImageOutputStreamSpi}.  It is up
66      * to the subclass to initialize instance variables and/or
67      * override method implementations in order to provide working
68      * versions of all methods.
69      */
ImageOutputStreamSpi()70     protected ImageOutputStreamSpi() {
71     }
72 
73     /**
74      * Constructs an {@code ImageOutputStreamSpi} with a given
75      * set of values.
76      *
77      * @param vendorName the vendor name.
78      * @param version a version identifier.
79      * @param outputClass a {@code Class} object indicating the
80      * legal object type for use by the
81      * {@code createOutputStreamInstance} method.
82      *
83      * @exception IllegalArgumentException if {@code vendorName}
84      * is {@code null}.
85      * @exception IllegalArgumentException if {@code version}
86      * is {@code null}.
87     */
ImageOutputStreamSpi(String vendorName, String version, Class<?> outputClass)88     public ImageOutputStreamSpi(String vendorName,
89                                 String version,
90                                 Class<?> outputClass) {
91         super(vendorName, version);
92         this.outputClass = outputClass;
93     }
94 
95     /**
96      * Returns a {@code Class} object representing the class or
97      * interface type that must be implemented by an output
98      * destination in order to be "wrapped" in an
99      * {@code ImageOutputStream} via the
100      * {@code createOutputStreamInstance} method.
101      *
102      * <p> Typical return values might include
103      * {@code OutputStream.class} or {@code File.class}, but
104      * any class may be used.
105      *
106      * @return a {@code Class} variable.
107      *
108      * @see #createOutputStreamInstance(Object, boolean, File)
109      */
getOutputClass()110     public Class<?> getOutputClass() {
111         return outputClass;
112     }
113 
114     /**
115      * Returns {@code true} if the {@code ImageOutputStream}
116      * implementation associated with this service provider can
117      * optionally make use of a cache {@code File} for improved
118      * performance and/or memory footrprint.  If {@code false},
119      * the value of the {@code cacheFile} argument to
120      * {@code createOutputStreamInstance} will be ignored.
121      *
122      * <p> The default implementation returns {@code false}.
123      *
124      * @return {@code true} if a cache file can be used by the
125      * output streams created by this service provider.
126      */
canUseCacheFile()127     public boolean canUseCacheFile() {
128         return false;
129     }
130 
131     /**
132      * Returns {@code true} if the {@code ImageOutputStream}
133      * implementation associated with this service provider requires
134      * the use of a cache {@code File}.
135      *
136      * <p> The default implementation returns {@code false}.
137      *
138      * @return {@code true} if a cache file is needed by the
139      * output streams created by this service provider.
140      */
needsCacheFile()141     public boolean needsCacheFile() {
142         return false;
143     }
144 
145     /**
146      * Returns an instance of the {@code ImageOutputStream}
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 output an object of the class type returned by
153      * {@code getOutputClass}.
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 ImageOutputStream} instance.
161      *
162      * @exception IllegalArgumentException if {@code output} 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 #getOutputClass
171      */
172     public abstract
createOutputStreamInstance(Object output, boolean useCache, File cacheDir)173         ImageOutputStream createOutputStreamInstance(Object output,
174                                                      boolean useCache,
175                                                      File cacheDir)
176         throws IOException;
177 
178     /**
179      * Returns an instance of the {@code ImageOutputStream}
180      * implementation associated with this service provider.  A cache
181      * file will be created in the system-dependent default
182      * temporary-file directory, if needed.
183      *
184      * @param output an object of the class type returned by
185      * {@code getOutputClass}.
186      *
187      * @return an {@code ImageOutputStream} instance.
188      *
189      * @exception IllegalArgumentException if {@code output} is
190      * not an instance of the correct class or is {@code null}.
191      * @exception IOException if a cache file is needed but cannot be
192      * created.
193      *
194      * @see #getOutputClass()
195      */
createOutputStreamInstance(Object output)196     public ImageOutputStream createOutputStreamInstance(Object output)
197         throws IOException {
198         return createOutputStreamInstance(output, true, null);
199     }
200 }
201