ImageInputStreamSpi.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * accompanied this code).
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package javax.imageio.spi;

import java.io.File;
import java.io.IOException;
import javax.imageio.stream.ImageInputStream;

/**
 * The service provider interface (SPI) for
 * {@code ImageInputStream}s.  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 {@code ImageInputStream}s 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 {@code 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 {@code 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 {@code 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 {@code ImageInputStream}
     * implementation associated with this service provider requires
     * the use of a cache {@code File}.  If {@code true},
     * the value of the {@code useCache} argument to
     * {@code createInputStreamInstance} will be ignored.
     *
     * <p> The default implementation returns {@code 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-{@code 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);
    }
}