public final class FileSystems extends Object
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.
| Modifier and Type | Method and Description |
|---|---|
static FileSystem |
getDefault()
Returns the default
FileSystem. |
static FileSystem |
getFileSystem(URI uri)
Returns a reference to an existing
FileSystem. |
static FileSystem |
newFileSystem(Path path,
ClassLoader loader)
Constructs a new
FileSystem to access the contents of a file as a
file system. |
static FileSystem |
newFileSystem(URI uri,
Map<String,?> env)
Constructs a new file system that is identified by a
URI |
static FileSystem |
newFileSystem(URI uri,
Map<String,?> env,
ClassLoader loader)
Constructs a new file system that is identified by a
URI |
public static FileSystem getDefault()
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.
public static FileSystem getFileSystem(URI uri)
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.
IllegalArgumentException - if the pre-conditions for the uri parameter are not metFileSystemNotFoundException - if the file system, identified by the URI, does not existProviderNotFoundException - if a provider supporting the URI scheme is not installedSecurityException - if a security manager is installed and it denies an unspecified
permissionpublic static FileSystem newFileSystem(URI uri, Map<String,?> env) throws IOException
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);
uri - the URI identifying the file systemenv - a map of provider specific properties to configure the file system;
may be emptyIllegalArgumentException - 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 invalidFileSystemAlreadyExistsException - if the file system has already been createdProviderNotFoundException - if a provider supporting the URI scheme is not installedIOException - if an I/O error occurs creating the file systemSecurityException - if a security manager is installed and it denies an unspecified
permission required by the file system provider implementationpublic static FileSystem newFileSystem(URI uri, Map<String,?> env, ClassLoader loader) throws IOException
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.
uri - the URI identifying the file systemenv - a map of provider specific properties to configure the file system;
may be emptyloader - the class loader to locate the provider or null to only
attempt to locate an installed providerIllegalArgumentException - 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 invalidFileSystemAlreadyExistsException - if the URI scheme identifies an installed provider and the file
system has already been createdProviderNotFoundException - if a provider supporting the URI scheme is not foundServiceConfigurationError - when an error occurs while loading a service providerIOException - an I/O error occurs creating the file systemSecurityException - if a security manager is installed and it denies an unspecified
permission required by the file system provider implementationpublic static FileSystem newFileSystem(Path path, ClassLoader loader) throws IOException
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.
path - the path to the fileloader - the class loader to locate the provider or null to only
attempt to locate an installed providerProviderNotFoundException - if a provider supporting this file type cannot be locatedServiceConfigurationError - when an error occurs while loading a service providerIOException - if an I/O error occursSecurityException - if a security manager is installed and it denies an unspecified
permission Submit a bug or feature
For further API reference and developer documentation, see Java SE Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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