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	/*
	* Copyright (c) 2007, 2021, 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
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package java.nio.file;

	import java.nio.file.spi.FileSystemProvider;
	import java.net.URI;
	import java.io.IOException;
	import java.security.AccessController;
	import java.security.PrivilegedAction;
	import java.lang.reflect.Constructor;
	import java.util.Collections;
	import java.util.Map;
	import java.util.ServiceConfigurationError;
	import java.util.ServiceLoader;

	import jdk.internal.misc.VM;
	import sun.nio.fs.DefaultFileSystemProvider;

	/**
	* Factory methods for file systems. This class defines the {@link #getDefault
	* getDefault} method to get the default file system and factory methods to
	* construct other types of file systems.
	*
	* <p> The first invocation of any of the methods defined by this class causes
	* the default {@link FileSystemProvider provider} to be loaded. The default
	* provider, identified by the URI scheme "file", creates the {@link FileSystem}
	* that provides access to the file systems accessible to the Java virtual
	* machine. If the process of loading or initializing the default provider fails
	* then an unspecified error is thrown.
	*
	* <p> The first invocation of the {@link FileSystemProvider#installedProviders()
	* installedProviders} method, by way of invoking any of the {@code
	* newFileSystem} methods defined by this class, locates and loads all
	* installed file system providers. Installed providers are loaded using the
	* service-provider loading facility defined by the {@link ServiceLoader} class.
	* Installed providers are loaded using the system class loader. If the
	* system class loader cannot be found then the platform class loader is used.
	* Providers are typically installed by placing them in a JAR file on the
	* application class path, the JAR file contains a
	* provider-configuration file named {@code java.nio.file.spi.FileSystemProvider}
	* in the resource directory {@code META-INF/services}, and the file lists one or
	* more fully-qualified names of concrete subclass of {@link FileSystemProvider}
	* that have a zero argument constructor.
	* The ordering that installed providers are located is implementation specific.
	* If a provider is instantiated and its {@link FileSystemProvider#getScheme()
	* getScheme} returns the same URI scheme of a provider that was previously
	* instantiated then the most recently instantiated duplicate is discarded. URI
	* schemes are compared without regard to case. During construction a provider
	* may safely access files associated with the default provider but care needs
	* to be taken to avoid circular loading of other installed providers. If
	* circular loading of installed providers is detected then an unspecified error
	* is thrown.
	*
	* <p> This class also defines factory methods that allow a {@link ClassLoader}
	* to be specified when locating a provider. As with installed providers, the
	* provider classes are identified by placing the provider configuration file
	* in the resource directory {@code META-INF/services}.
	*
	* <p> If a thread initiates the loading of the installed file system providers
	* and another thread invokes a method that also attempts to load the providers
	* then the method will block until the loading completes.
	*
	* @since 1.7
	*/

	public final class FileSystems {
	private FileSystems() { }

	// lazy initialization of default file system
	private static class DefaultFileSystemHolder {
	static final FileSystem defaultFileSystem = defaultFileSystem();

	// returns default file system
	private static FileSystem defaultFileSystem() {
	// load default provider
	@SuppressWarnings("removal")
	FileSystemProvider provider = AccessController
	.doPrivileged(new PrivilegedAction<>() {
	public FileSystemProvider run() {
	return getDefaultProvider();
	}
	});

	// return file system
	return provider.getFileSystem(URI.create("file:///"));
	}

	// returns default provider
	private static FileSystemProvider getDefaultProvider() {
	// start with the platform's default file system provider
	FileSystemProvider provider = DefaultFileSystemProvider.instance();

	// if the property java.nio.file.spi.DefaultFileSystemProvider is
	// set then its value is the name of the default provider (or a list)
	String prop = "java.nio.file.spi.DefaultFileSystemProvider";
	String propValue = System.getProperty(prop);
	if (propValue != null) {
	for (String cn: propValue.split(",")) {
	try {
	Class<?> c = Class
	.forName(cn, true, ClassLoader.getSystemClassLoader());
	Constructor<?> ctor = c
	.getDeclaredConstructor(FileSystemProvider.class);
	provider = (FileSystemProvider)ctor.newInstance(provider);

	// must be "file"
	if (!provider.getScheme().equals("file"))
	throw new Error("Default provider must use scheme 'file'");

	} catch (Exception x) {
	throw new Error(x);
	}
	}
	}
	return provider;
	}
	}

	/**
	* Returns the default {@code FileSystem}. The default file system creates
	* objects that provide access to the file systems accessible to the Java
	* virtual machine. The <em>working directory</em> of the file system is
	* the current user directory, named by the system property {@code user.dir}.
	* This allows for interoperability with the {@link java.io.File java.io.File}
	* class.
	*
	* <p> The first invocation of any of the methods defined by this class
	* locates the default {@link FileSystemProvider provider} object. Where the
	* system property {@code java.nio.file.spi.DefaultFileSystemProvider} is
	* not defined then the default provider is a system-default provider that
	* is invoked to create the default file system.
	*
	* <p> If the system property {@code java.nio.file.spi.DefaultFileSystemProvider}
	* is defined then it is taken to be a list of one or more fully-qualified
	* names of concrete provider classes identified by the URI scheme
	* {@code "file"}. Where the property is a list of more than one name then
	* the names are separated by a comma. Each class is loaded, using the system
	* class loader, and instantiated by invoking a one argument constructor
	* whose formal parameter type is {@code FileSystemProvider}. The providers
	* are loaded and instantiated in the order they are listed in the property.
	* If this process fails or a provider's scheme is not equal to {@code "file"}
	* then an unspecified error is thrown. URI schemes are normally compared
	* without regard to case but for the default provider, the scheme is
	* required to be {@code "file"}. The first provider class is instantiated
	* by invoking it with a reference to the system-default provider.
	* The second provider class is instantiated by invoking it with a reference
	* to the first provider instance. The third provider class is instantiated
	* by invoking it with a reference to the second instance, and so on. The
	* last provider to be instantiated becomes the default provider; its {@code
	* getFileSystem} method is invoked with the URI {@code "file:///"} to
	* get a reference to the default file system.
	*
	* <p> Subsequent invocations of this method return the file system that was
	* returned by the first invocation.
	*
	* @return the default file system
	*/
	public static FileSystem getDefault() {
	if (VM.isModuleSystemInited()) {
	return DefaultFileSystemHolder.defaultFileSystem;
	} else {
	// always use the platform's default file system during startup
	return DefaultFileSystemProvider.theFileSystem();
	}
	}

	/**
	* Returns a reference to an existing {@code FileSystem}.
	*
	* <p> This method iterates over the {@link FileSystemProvider#installedProviders()
	* installed} providers to locate the provider that is identified by the URI
	* {@link URI#getScheme scheme} of the given URI. URI schemes are compared
	* without regard to case. The exact form of the URI is highly provider
	* dependent. If found, the provider's {@link FileSystemProvider#getFileSystem
	* getFileSystem} method is invoked to obtain a reference to the {@code
	* FileSystem}.
	*
	* <p> Once a file system created by this provider is {@link FileSystem#close
	* closed} it is provider-dependent if this method returns a reference to
	* the closed file system or throws {@link FileSystemNotFoundException}.
	* If the provider allows a new file system to be created with the same URI
	* as a file system it previously created then this method throws the
	* exception if invoked after the file system is closed (and before a new
	* instance is created by the {@link #newFileSystem newFileSystem} method).
	*
	* <p> If a security manager is installed then a provider implementation
	* may require to check a permission before returning a reference to an
	* existing file system. In the case of the {@link FileSystems#getDefault
	* default} file system, no permission check is required.
	*
	* @param uri the URI to locate the file system
	*
	* @return the reference to the file system
	*
	* @throws IllegalArgumentException
	* if the pre-conditions for the {@code uri} parameter are not met
	* @throws FileSystemNotFoundException
	* if the file system, identified by the URI, does not exist
	* @throws ProviderNotFoundException
	* if a provider supporting the URI scheme is not installed
	* @throws SecurityException
	* if a security manager is installed and it denies an unspecified
	* permission
	*/
	public static FileSystem getFileSystem(URI uri) {
	String scheme = uri.getScheme();
	if (scheme == null) {
	throw new IllegalArgumentException(uri.toString());
	}
	for (FileSystemProvider provider: FileSystemProvider.installedProviders()) {
	if (scheme.equalsIgnoreCase(provider.getScheme())) {
	return provider.getFileSystem(uri);
	}
	}
	throw new ProviderNotFoundException("Provider \"" + scheme + "\" not found");
	}

	/**
	* Constructs a new file system that is identified by a {@link URI}
	*
	* <p> This method iterates over the {@link FileSystemProvider#installedProviders()
	* installed} providers to locate the provider that is identified by the URI
	* {@link URI#getScheme scheme} of the given URI. URI schemes are compared
	* without regard to case. The exact form of the URI is highly provider
	* dependent. If found, the provider's {@link FileSystemProvider#newFileSystem(URI,Map)
	* newFileSystem(URI,Map)} method is invoked to construct the new file system.
	*
	* <p> Once a file system is {@link FileSystem#close closed} it is
	* provider-dependent if the provider allows a new file system to be created
	* with the same URI as a file system it previously created.
	*
	* <p> <b>Usage Example:</b>
	* Suppose there is a provider identified by the scheme {@code "memory"}
	* installed:
	* <pre>
	* FileSystem fs = FileSystems.newFileSystem(URI.create("memory:///?name=logfs"),
	* Map.of("capacity", "16G", "blockSize", "4k"));
	* </pre>
	*
	* @param uri
	* the URI identifying the file system
	* @param env
	* a map of provider specific properties to configure the file system;
	* may be empty
	*
	* @return a new file system
	*
	* @throws IllegalArgumentException
	* if the pre-conditions for the {@code uri} parameter are not met,
	* or the {@code env} parameter does not contain properties required
	* by the provider, or a property value is invalid
	* @throws FileSystemAlreadyExistsException
	* if the file system has already been created
	* @throws ProviderNotFoundException
	* if a provider supporting the URI scheme is not installed
	* @throws IOException
	* if an I/O error occurs creating the file system
	* @throws SecurityException
	* if a security manager is installed and it denies an unspecified
	* permission required by the file system provider implementation
	*/
	public static FileSystem newFileSystem(URI uri, Map<String,?> env)
	throws IOException
	{
	return newFileSystem(uri, env, null);
	}

	/**
	* Constructs a new file system that is identified by a {@link URI}
	*
	* <p> This method first attempts to locate an installed provider in exactly
	* the same manner as the {@link #newFileSystem(URI,Map) newFileSystem(URI,Map)}
	* method. If none of the installed providers support the URI scheme then an
	* attempt is made to locate the provider using the given class loader. If a
	* provider supporting the URI scheme is located then its {@link
	* FileSystemProvider#newFileSystem(URI,Map) newFileSystem(URI,Map)} is
	* invoked to construct the new file system.
	*
	* @param uri
	* the URI identifying the file system
	* @param env
	* a map of provider specific properties to configure the file system;
	* may be empty
	* @param loader
	* the class loader to locate the provider or {@code null} to only
	* attempt to locate an installed provider
	*
	* @return a new file system
	*
	* @throws IllegalArgumentException
	* if the pre-conditions for the {@code uri} parameter are not met,
	* or the {@code env} parameter does not contain properties required
	* by the provider, or a property value is invalid
	* @throws FileSystemAlreadyExistsException
	* if the URI scheme identifies an installed provider and the file
	* system has already been created
	* @throws ProviderNotFoundException
	* if a provider supporting the URI scheme is not found
	* @throws ServiceConfigurationError
	* when an error occurs while loading a service provider
	* @throws IOException
	* an I/O error occurs creating the file system
	* @throws SecurityException
	* if a security manager is installed and it denies an unspecified
	* permission required by the file system provider implementation
	*/
	public static FileSystem newFileSystem(URI uri, Map<String,?> env, ClassLoader loader)
	throws IOException
	{
	String scheme = uri.getScheme();

	// check installed providers
	for (FileSystemProvider provider : FileSystemProvider.installedProviders()) {
	if (scheme.equalsIgnoreCase(provider.getScheme())) {
	try {
	return provider.newFileSystem(uri, env);
	} catch (UnsupportedOperationException uoe) {
	}
	}
	}

	// if not found, use service-provider loading facility
	if (loader != null) {
	ServiceLoader<FileSystemProvider> sl = ServiceLoader
	.load(FileSystemProvider.class, loader);
	for (FileSystemProvider provider : sl) {
	if (scheme.equalsIgnoreCase(provider.getScheme())) {
	try {
	return provider.newFileSystem(uri, env);
	} catch (UnsupportedOperationException uoe) {
	}
	}
	}
	}

	throw new ProviderNotFoundException("Provider \"" + scheme + "\" not found");
	}

	/**
	* Constructs a new {@code FileSystem} to access the contents of a file as a
	* file system.
	*
	* <p> This method makes use of specialized providers that create pseudo file
	* systems where the contents of one or more files is treated as a file
	* system.
	*
	* <p> This method first attempts to locate an installed provider in exactly
	* the same manner as the {@link #newFileSystem(Path, Map, ClassLoader)
	* newFileSystem(Path, Map, ClassLoader)} method with an empty map. If none
	* of the installed providers return a {@code FileSystem} then an attempt is
	* made to locate the provider using the given class loader. If a provider
	* returns a file system then the lookup terminates and the file system is
	* returned.
	*
	* @param path
	* the path to the file
	* @param loader
	* the class loader to locate the provider or {@code null} to only
	* attempt to locate an installed provider
	*
	* @return a new file system
	*
	* @throws ProviderNotFoundException
	* if a provider supporting this file type cannot be located
	* @throws ServiceConfigurationError
	* when an error occurs while loading a service provider
	* @throws IOException
	* if an I/O error occurs
	* @throws SecurityException
	* if a security manager is installed and it denies an unspecified
	* permission
	*/
	public static FileSystem newFileSystem(Path path,
	ClassLoader loader)
	throws IOException
	{
	return newFileSystem(path, Map.of(), loader);
	}

	/**
	* Constructs a new {@code FileSystem} to access the contents of a file as a
	* file system.
	*
	* <p> This method makes use of specialized providers that create pseudo file
	* systems where the contents of one or more files is treated as a file
	* system.
	*
	* <p> This method first attempts to locate an installed provider in exactly
	* the same manner as the {@link #newFileSystem(Path,Map,ClassLoader)
	* newFileSystem(Path, Map, ClassLoader)} method. If found, the provider's
	* {@link FileSystemProvider#newFileSystem(Path, Map) newFileSystem(Path, Map)}
	* method is invoked to construct the new file system.
	*
	* @param path
	* the path to the file
	* @param env
	* a map of provider specific properties to configure the file system;
	* may be empty
	*
	* @return a new file system
	*
	* @throws ProviderNotFoundException
	* if a provider supporting this file type cannot be located
	* @throws ServiceConfigurationError
	* when an error occurs while loading a service provider
	* @throws IOException
	* if an I/O error occurs
	* @throws SecurityException
	* if a security manager is installed and it denies an unspecified
	* permission
	*
	* @since 13
	*/
	public static FileSystem newFileSystem(Path path, Map<String,?> env)
	throws IOException
	{
	return newFileSystem(path, env, null);
	}

	/**
	* Constructs a new {@code FileSystem} to access the contents of a file as a
	* file system.
	*
	* <p> This method makes use of specialized providers that create pseudo file
	* systems where the contents of one or more files is treated as a file
	* system.
	*
	* <p> This method first attempts to locate an installed provider in exactly
	* the same manner as the {@link #newFileSystem(Path,Map,ClassLoader)
	* newFileSystem(Path, Map, ClassLoader)} method. If found, the provider's
	* {@link FileSystemProvider#newFileSystem(Path, Map) newFileSystem(Path, Map)}
	* method is invoked with an empty map to construct the new file system.
	*
	* @param path
	* the path to the file
	*
	* @return a new file system
	*
	* @throws ProviderNotFoundException
	* if a provider supporting this file type cannot be located
	* @throws ServiceConfigurationError
	* when an error occurs while loading a service provider
	* @throws IOException
	* if an I/O error occurs
	* @throws SecurityException
	* if a security manager is installed and it denies an unspecified
	* permission
	*
	* @since 13
	*/
	public static FileSystem newFileSystem(Path path) throws IOException {
	return newFileSystem(path, Map.of(), null);
	}

	/**
	* Constructs a new {@code FileSystem} to access the contents of a file as a
	* file system.
	*
	* <p> This method makes use of specialized providers that create pseudo file
	* systems where the contents of one or more files is treated as a file
	* system.
	*
	* <p> This method iterates over the {@link FileSystemProvider#installedProviders()
	* installed} providers. It invokes, in turn, each provider's {@link
	* FileSystemProvider#newFileSystem(Path,Map) newFileSystem(Path,Map)}
	* method. If a provider returns a file system then the iteration
	* terminates and the file system is returned.
	* If none of the installed providers return a {@code FileSystem} then
	* an attempt is made to locate the provider using the given class loader.
	* If a provider returns a file
	* system, then the lookup terminates and the file system is returned.
	*
	* @param path
	* the path to the file
	* @param env
	* a map of provider specific properties to configure the file system;
	* may be empty
	* @param loader
	* the class loader to locate the provider or {@code null} to only
	* attempt to locate an installed provider
	*
	* @return a new file system
	*
	* @throws ProviderNotFoundException
	* if a provider supporting this file type cannot be located
	* @throws ServiceConfigurationError
	* when an error occurs while loading a service provider
	* @throws IOException
	* if an I/O error occurs
	* @throws SecurityException
	* if a security manager is installed and it denies an unspecified
	* permission
	*
	* @since 13
	*/
	public static FileSystem newFileSystem(Path path, Map<String,?> env,
	ClassLoader loader)
	throws IOException
	{
	if (path == null)
	throw new NullPointerException();
	// check installed providers
	for (FileSystemProvider provider: FileSystemProvider.installedProviders()) {
	try {
	return provider.newFileSystem(path, env);
	} catch (UnsupportedOperationException uoe) {
	}
	}

	// if not found, use service-provider loading facility
	if (loader != null) {
	ServiceLoader<FileSystemProvider> sl = ServiceLoader
	.load(FileSystemProvider.class, loader);
	for (FileSystemProvider provider: sl) {
	try {
	return provider.newFileSystem(path, env);
	} catch (UnsupportedOperationException uoe) {
	}
	}
	}

	throw new ProviderNotFoundException("Provider not found");
	}
	}

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