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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 {@link #getDefault
* 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 {@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.
*
*
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.
*
*
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}.
*
*
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() {
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 {@code 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 {@code user.dir}.
* This allows for interoperability with the {@link java.io.File java.io.File}
* class.
*
* 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.
*
*
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.
*
*
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 {@code FileSystem}.
*
*
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}.
*
*
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).
*
*
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 {@link URI}
*
*
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.
*
*
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.
*
*
Usage Example:
* Suppose there is a provider identified by the scheme {@code "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);
*
*
* @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 env)
throws IOException
{
return newFileSystem(uri, env, null);
}
/**
* Constructs a new file system that is identified by a {@link URI}
*
* 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 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 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 {@code 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 {@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 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 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");
}
}