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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
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 *
 * 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).
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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.util.*;
import java.lang.reflect.Constructor;


Factory methods for file systems. This class defines the 
getDefault method to get the default file system and factory methods to construct other types of file systems. 
 The first invocation of any of the methods defined by this class causes the default provider to be loaded. The default provider, identified by the URI scheme "file", creates the 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. 
 The first invocation of the 
installedProviders method, by way of invoking any of the 
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 ServiceLoader class. Installed providers are loaded using the system class loader. If the system class loader cannot be found then the extension class loader is used; if there is no extension class loader then the bootstrap class loader is used. Providers are typically installed by placing them in a JAR file on the application class path or in the extension directory, the JAR file contains a provider-configuration file named java.nio.file.spi.FileSystemProvider in the resource directory META-INF/services, and the file lists one or more fully-qualified names of concrete subclass of FileSystemProvider that have a zero argument constructor. The ordering that installed providers are located is implementation specific. If a provider is instantiated and its 
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. 
 This class also defines factory methods that allow a 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 META-INF/services. 
 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
/**
 * 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 extension class loader is used;
 * if there is no extension class loader then the bootstrap class loader is used.
 * Providers are typically installed by placing them in a JAR file on the
 * application class path or in the extension directory, 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
            FileSystemProvider provider = AccessController
                .doPrivileged(new PrivilegedAction<FileSystemProvider>() {
                    public FileSystemProvider run() {
                        return getDefaultProvider();
                    }
                });

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

        // returns default provider
        private static FileSystemProvider getDefaultProvider() {
            FileSystemProvider provider = sun.nio.fs.DefaultFileSystemProvider.create();

            // if the property java.nio.file.spi.DefaultFileSystemProvider is
            // set then its value is the name of the default provider (or a list)
            String propValue = System
                .getProperty("java.nio.file.spi.DefaultFileSystemProvider");
            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 FileSystem. The default file system creates objects that provide access to the file systems accessible to the Java virtual machine. The working directory of the file system is the current user directory, named by the system property user.dir. This allows for interoperability with the java.io.File class. 
 The first invocation of any of the methods defined by this class locates the default provider object. Where the system property 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. 
 If the system property 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 "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 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 "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 "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 
getFileSystem method is invoked with the URI "file:///" to get a reference to the default file system. 
 Subsequent invocations of this method return the file system that was
returned by the first invocation.

Returns: the default file system
/**
     * 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() {
        return DefaultFileSystemHolder.defaultFileSystem;
    }

    
Returns a reference to an existing FileSystem. 
 This method iterates over the 
installed providers to locate the provider that is identified by the URI 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 
getFileSystem method is invoked to obtain a reference to the 
FileSystem. 
 Once a file system created by this provider is 
closed it is provider-dependent if this method returns a reference to the closed file system or throws 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 newFileSystem method). 
 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 
default file system, no permission check is required. 
Params:
  • uri –  the URI to locate the file system
Throws:
Returns: the reference to the file system
/**
     * 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();
        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 URI 
 This method iterates over the 
installed providers to locate the provider that is identified by the URI 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 
newFileSystem(URI,Map) method is invoked to construct the new file system. 
 Once a file system is 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. 
 Usage Example: Suppose there is a provider identified by the scheme "memory" installed: 
  Map<String,String> env = new HashMap<>();
  env.put("capacity", "16G");
  env.put("blockSize", "4k");
  FileSystem fs = FileSystems.newFileSystem(URI.create("memory:///?name=logfs"), env);



Params:
  • uri – 
         the URI identifying the file system
  • env – 
         a map of provider specific properties to configure the file system;
         may be empty
Throws:
  • IllegalArgumentException –  if the pre-conditions for the uri parameter are not met, or the env parameter does not contain properties required by the provider, or a property value is invalid
  • FileSystemAlreadyExistsException – 
         if the file system has already been created
  • ProviderNotFoundException – 
         if a provider supporting the URI scheme is not installed
  • IOException – 
         if an I/O error occurs creating the file system
  • SecurityException – 
         if a security manager is installed and it denies an unspecified
         permission required by the file system provider implementation
Returns: a new file system
/**
     * 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>
     *   Map&lt;String,String&gt; env = new HashMap&lt;&gt;();
     *   env.put("capacity", "16G");
     *   env.put("blockSize", "4k");
     *   FileSystem fs = FileSystems.newFileSystem(URI.create("memory:///?name=logfs"), env);
     * </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 URI 
 This method first attempts to locate an installed provider in exactly the same manner as the 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 newFileSystem(URI,Map) is invoked to construct the new file system. 
Params:
  • uri – 
         the URI identifying the file system
  • env – 
         a map of provider specific properties to configure the file system;
         may be empty
  • loader –  the class loader to locate the provider or null to only attempt to locate an installed provider
Throws:
  • IllegalArgumentException –  if the pre-conditions for the uri parameter are not met, or the env parameter does not contain properties required by the provider, or a property value is invalid
  • FileSystemAlreadyExistsException – 
         if the URI scheme identifies an installed provider and the file
         system has already been created
  • ProviderNotFoundException – 
         if a provider supporting the URI scheme is not found
  • ServiceConfigurationError – 
         when an error occurs while loading a service provider
  • IOException – 
         an I/O error occurs creating the file system
  • SecurityException – 
         if a security manager is installed and it denies an unspecified
         permission required by the file system provider implementation
Returns: a new file system
/**
     * 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())) {
                return provider.newFileSystem(uri, env);
            }
        }

        // 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())) {
                    return provider.newFileSystem(uri, env);
                }
            }
        }

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

    
Constructs a new FileSystem to access the contents of a file as a file system. 
 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.

 This method iterates over the 
installed providers. It invokes, in turn, each provider's newFileSystem(Path,Map) method with an empty map. 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 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. 
Params:
  • path – 
         the path to the file
  • loader –  the class loader to locate the provider or null to only attempt to locate an installed provider
Throws:
Returns: a new file system
/**
     * 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
     * with an empty map. 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   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
    {
        if (path == null)
            throw new NullPointerException();
        Map<String,?> env = Collections.emptyMap();

        // 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");
    }
}