/*
 * @(#)ImageIO.java	1.89 05/12/21
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package javax.imageio;

import java.awt.image.BufferedImage;
import java.awt.image.RenderedImage;
import java.io.File;
import java.io.InputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.lang.reflect.Method;
import java.net.URL;
import java.security.AccessController;
import java.util.Arrays;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Set;
import javax.imageio.spi.IIORegistry;
import javax.imageio.spi.ImageReaderSpi;
import javax.imageio.spi.ImageReaderWriterSpi;
import javax.imageio.spi.ImageWriterSpi;
import javax.imageio.spi.ImageInputStreamSpi;
import javax.imageio.spi.ImageOutputStreamSpi;
import javax.imageio.spi.ImageTranscoderSpi;
import javax.imageio.spi.ServiceRegistry;
import javax.imageio.stream.ImageInputStream;
import javax.imageio.stream.ImageOutputStream;
import sun.awt.AppContext;
import sun.security.action.GetPropertyAction;

/**
 * A class containing static convenience methods for locating
 * <code>ImageReader</code>s and <code>ImageWriter</code>s, and
 * performing simple encoding and decoding.
 *
 * @version 0.5
 */
public final class ImageIO {

    private static final IIORegistry theRegistry =
        IIORegistry.getDefaultInstance();

    /**
     * Constructor is private to prevent instantiation.
     */
    private ImageIO() {}

    /**
     * Scans for plug-ins on the application class path,
     * loads their service provider classes, and registers a service
     * provider instance for each one found with the
     * <code>IIORegistry</code>.
     * 
     * <p>This method is needed because the application class path can
     * theoretically change, or additional plug-ins may become available.
     * Rather than re-scanning the classpath on every invocation of the
     * API, the class path is scanned automatically only on the first
     * invocation. Clients can call this method to prompt a re-scan.
     * Thus this method need only be invoked by sophisticated applications
     * which dynamically make new plug-ins available at runtime.
     *
     * <p> The <code>getResources</code> method of the context
     * <code>ClassLoader</code> is used locate JAR files containing
     * files named
     * <code>META-INF/services/javax.imageio.spi.</code><i>classname</i>,
     * where <i>classname</i> is one of <code>ImageReaderSpi</code>,
     * <code>ImageWriterSpi</code>, <code>ImageTranscoderSpi</code>,
     * <code>ImageInputStreamSpi</code>, or
     * <code>ImageOutputStreamSpi</code>, along the application class
     * path.
     *
     * <p> The contents of the located files indicate the names of
     * actual implementation classes which implement the
     * aforementioned service provider interfaces; the default class
     * loader is then used to load each of these classes and to
     * instantiate an instance of each class, which is then placed
     * into the registry for later retrieval.
     *
     * <p> The exact set of locations searched depends on the
     * implementation of the Java runtime enviroment.
     * 
     * @see ClassLoader#getResources
     */
    public static void scanForPlugins() {
        theRegistry.registerApplicationClasspathSpis();
    }

    // ImageInputStreams

    /**
     * A class to hold information about caching.  Each
     * <code>ThreadGroup</code> will have its own copy