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/*
 * Copyright (c) 1999, 2013, 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
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 */

package javax.imageio.spi;

import java.security.PrivilegedAction;
import java.security.AccessController;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.Set;
import java.util.Vector;
import com.sun.imageio.spi.FileImageInputStreamSpi;
import com.sun.imageio.spi.FileImageOutputStreamSpi;
import com.sun.imageio.spi.InputStreamImageInputStreamSpi;
import com.sun.imageio.spi.OutputStreamImageOutputStreamSpi;
import com.sun.imageio.spi.RAFImageInputStreamSpi;
import com.sun.imageio.spi.RAFImageOutputStreamSpi;
import com.sun.imageio.plugins.gif.GIFImageReaderSpi;
import com.sun.imageio.plugins.gif.GIFImageWriterSpi;
import com.sun.imageio.plugins.jpeg.JPEGImageReaderSpi;
import com.sun.imageio.plugins.jpeg.JPEGImageWriterSpi;
import com.sun.imageio.plugins.png.PNGImageReaderSpi;
import com.sun.imageio.plugins.png.PNGImageWriterSpi;
import com.sun.imageio.plugins.bmp.BMPImageReaderSpi;
import com.sun.imageio.plugins.bmp.BMPImageWriterSpi;
import com.sun.imageio.plugins.wbmp.WBMPImageReaderSpi;
import com.sun.imageio.plugins.wbmp.WBMPImageWriterSpi;
import sun.awt.AppContext;
import java.util.ServiceLoader;
import java.util.ServiceConfigurationError;


A registry for service provider instances.  Service provider
classes may be detected at run time by means of meta-information in
the JAR files containing them.  The intent is that it be relatively
inexpensive to load and inspect all available service provider
classes.  These classes may them be used to locate and instantiate
more heavyweight classes that will perform actual work, in this
case instances of ImageReader,
ImageWriter, ImageTranscoder,
ImageInputStream, and ImageOutputStream.

 Service providers found on the system classpath (typically
the lib/ext directory in the Java
installation directory) are automatically loaded as soon as this class is
instantiated.

 When the registerApplicationClasspathSpis method
is called, service provider instances declared in the
meta-information section of JAR files on the application class path
are loaded.  To declare a service provider, a services
subdirectory is placed within the META-INF directory
that is present in every JAR file.  This directory contains a file
for each service provider interface that has one or more
implementation classes present in the JAR file.  For example, if
the JAR file contained a class named
com.mycompany.imageio.MyFormatReaderSpi which
implements the ImageReaderSpi interface, the JAR file
would contain a file named:

META-INF/services/javax.imageio.spi.ImageReaderSpi


containing the line:

com.mycompany.imageio.MyFormatReaderSpi



 The service provider classes are intended to be lightweight
and quick to load.  Implementations of these interfaces
should avoid complex dependencies on other classes and on
native code.

 It is also possible to manually add service providers not found
automatically, as well as to remove those that are using the
interfaces of the ServiceRegistry class.  Thus
the application may customize the contents of the registry as it
sees fit.

 For more details on declaring service providers, and the JAR
format in general, see the 
JAR File Specification.

/**
 * A registry for service provider instances.  Service provider
 * classes may be detected at run time by means of meta-information in
 * the JAR files containing them.  The intent is that it be relatively
 * inexpensive to load and inspect all available service provider
 * classes.  These classes may them be used to locate and instantiate
 * more heavyweight classes that will perform actual work, in this
 * case instances of <code>ImageReader</code>,
 * <code>ImageWriter</code>, <code>ImageTranscoder</code>,
 * <code>ImageInputStream</code>, and <code>ImageOutputStream</code>.
 *
 * <p> Service providers found on the system classpath (typically
 * the <code>lib/ext</code> directory in the Java
 * installation directory) are automatically loaded as soon as this class is
 * instantiated.
 *
 * <p> When the <code>registerApplicationClasspathSpis</code> method
 * is called, service provider instances declared in the
 * meta-information section of JAR files on the application class path
 * are loaded.  To declare a service provider, a <code>services</code>
 * subdirectory is placed within the <code>META-INF</code> directory
 * that is present in every JAR file.  This directory contains a file
 * for each service provider interface that has one or more
 * implementation classes present in the JAR file.  For example, if
 * the JAR file contained a class named
 * <code>com.mycompany.imageio.MyFormatReaderSpi</code> which
 * implements the <code>ImageReaderSpi</code> interface, the JAR file
 * would contain a file named:
 *
 * <pre>
 * META-INF/services/javax.imageio.spi.ImageReaderSpi
 * </pre>
 *
 * containing the line:
 *
 * <pre>
 * com.mycompany.imageio.MyFormatReaderSpi
 * </pre>
 *
 * <p> The service provider classes are intended to be lightweight
 * and quick to load.  Implementations of these interfaces
 * should avoid complex dependencies on other classes and on
 * native code.
 *
 * <p> It is also possible to manually add service providers not found
 * automatically, as well as to remove those that are using the
 * interfaces of the <code>ServiceRegistry</code> class.  Thus
 * the application may customize the contents of the registry as it
 * sees fit.
 *
 * <p> For more details on declaring service providers, and the JAR
 * format in general, see the <a
 * href="{@docRoot}/../technotes/guides/jar/jar.html">
 * JAR File Specification</a>.
 *
 */
public final class IIORegistry extends ServiceRegistry {

    
A Vector containing the valid IIO registry
categories (superinterfaces) to be used in the constructor.

/**
     * A <code>Vector</code> containing the valid IIO registry
     * categories (superinterfaces) to be used in the constructor.
     */
    private static final Vector initialCategories = new Vector(5);

    static {
        initialCategories.add(ImageReaderSpi.class);
        initialCategories.add(ImageWriterSpi.class);
        initialCategories.add(ImageTranscoderSpi.class);
        initialCategories.add(ImageInputStreamSpi.class);
        initialCategories.add(ImageOutputStreamSpi.class);
    }

    
Set up the valid service provider categories and automatically
register all available service providers.

 The constructor is private in order to prevent creation of
additional instances.

/**
     * Set up the valid service provider categories and automatically
     * register all available service providers.
     *
     * <p> The constructor is private in order to prevent creation of
     * additional instances.
     */
    private IIORegistry() {
        super(initialCategories.iterator());
        registerStandardSpis();
        registerApplicationClasspathSpis();
    }

    
Returns the default IIORegistry instance used by
the Image I/O API.  This instance should be used for all
registry functions.

 Each ThreadGroup will receive its own
instance; this allows different Applets in the
same browser (for example) to each have their own registry.

Returns:the default registry for the current
ThreadGroup.
/**
     * Returns the default <code>IIORegistry</code> instance used by
     * the Image I/O API.  This instance should be used for all
     * registry functions.
     *
     * <p> Each <code>ThreadGroup</code> will receive its own
     * instance; this allows different <code>Applet</code>s in the
     * same browser (for example) to each have their own registry.
     *
     * @return the default registry for the current
     * <code>ThreadGroup</code>.
     */
    public static IIORegistry getDefaultInstance() {
        AppContext context = AppContext.getAppContext();
        IIORegistry registry =
            (IIORegistry)context.get(IIORegistry.class);
        if (registry == null) {
            // Create an instance for this AppContext
            registry = new IIORegistry();
            context.put(IIORegistry.class, registry);
        }
        return registry;
    }

    private void registerStandardSpis() {
        // Hardwire standard SPIs
        registerServiceProvider(new GIFImageReaderSpi());
        registerServiceProvider(new GIFImageWriterSpi());
        registerServiceProvider(new BMPImageReaderSpi());
        registerServiceProvider(new BMPImageWriterSpi());
        registerServiceProvider(new WBMPImageReaderSpi());
        registerServiceProvider(new WBMPImageWriterSpi());
        registerServiceProvider(new PNGImageReaderSpi());
        registerServiceProvider(new PNGImageWriterSpi());
        registerServiceProvider(new JPEGImageReaderSpi());
        registerServiceProvider(new JPEGImageWriterSpi());
        registerServiceProvider(new FileImageInputStreamSpi());
        registerServiceProvider(new FileImageOutputStreamSpi());
        registerServiceProvider(new InputStreamImageInputStreamSpi());
        registerServiceProvider(new OutputStreamImageOutputStreamSpi());
        registerServiceProvider(new RAFImageInputStreamSpi());
        registerServiceProvider(new RAFImageOutputStreamSpi());

        registerInstalledProviders();
    }

    
Registers all available service providers found on the
application class path, using the default
ClassLoader.  This method is typically invoked by
the ImageIO.scanForPlugins method.

See Also:
/**
     * Registers all available service providers found on the
     * application class path, using the default
     * <code>ClassLoader</code>.  This method is typically invoked by
     * the <code>ImageIO.scanForPlugins</code> method.
     *
     * @see javax.imageio.ImageIO#scanForPlugins
     * @see ClassLoader#getResources
     */
    public void registerApplicationClasspathSpis() {
        // FIX: load only from application classpath

        ClassLoader loader = Thread.currentThread().getContextClassLoader();

        Iterator categories = getCategories();
        while (categories.hasNext()) {
            Class<IIOServiceProvider> c = (Class)categories.next();
            Iterator<IIOServiceProvider> riter =
                    ServiceLoader.load(c, loader).iterator();
            while (riter.hasNext()) {
                try {
                    // Note that the next() call is required to be inside
                    // the try/catch block; see 6342404.
                    IIOServiceProvider r = riter.next();
                    registerServiceProvider(r);
                } catch (ServiceConfigurationError err) {
                    if (System.getSecurityManager() != null) {
                        // In the applet case, we will catch the  error so
                        // registration of other plugins can  proceed
                        err.printStackTrace();
                    } else {
                        // In the application case, we will  throw the
                        // error to indicate app/system  misconfiguration
                        throw err;
                    }
                }
            }
        }
    }

    private void registerInstalledProviders() {
        /*
          We need to load installed providers from the
          system classpath (typically the <code>lib/ext</code>
          directory in in the Java installation directory)
          in the privileged mode in order to
          be able read corresponding jar files even if
          file read capability is restricted (like the
          applet context case).
         */
        PrivilegedAction doRegistration =
            new PrivilegedAction() {
                public Object run() {
                    Iterator categories = getCategories();
                    while (categories.hasNext()) {
                        Class<IIOServiceProvider> c = (Class)categories.next();
                        for (IIOServiceProvider p : ServiceLoader.loadInstalled(c)) {
                            registerServiceProvider(p);
                        }
                    }
                    return this;
                }
            };

        AccessController.doPrivileged(doRegistration);
    }
}