public abstract class FileSystem extends Object implements Closeable
The default file system, obtained by invoking the FileSystems.getDefault method, provides access to the file system that is
accessible to the Java virtual machine. The FileSystems class defines
methods to create file systems that provide access to other types of (custom)
file systems.
A file system is the factory for several types of objects:
The getPath method converts a system dependent
path string, returning a Path object that may be used
to locate and access a file.
The getPathMatcher method is used
to create a PathMatcher that performs match operations on
paths.
The getFileStores method returns an iterator
over the underlying file-stores.
The getUserPrincipalLookupService
method returns the UserPrincipalLookupService to lookup users or
groups by name.
The newWatchService method creates a
WatchService that may be used to watch objects for changes and
events.
File systems vary greatly. In some cases the file system is a single
hierarchy of files with one top-level root directory. In other cases it may
have several distinct file hierarchies, each with its own top-level root
directory. The getRootDirectories method may be
used to iterate over the root directories in the file system. A file system
is typically composed of one or more underlying file-stores
that provide the storage for the files. Theses file stores can also vary in
the features they support, and the file attributes or meta-data that
they associate with files.
A file system is open upon creation and can be closed by invoking its
close method. Once closed, any further attempt to access
objects in the file system cause ClosedFileSystemException to be
thrown. File systems created by the default provider
cannot be closed.
A FileSystem can provide read-only or read-write access to the
file system. Whether or not a file system provides read-only access is
established when the FileSystem is created and can be tested by invoking
its isReadOnly method. Attempts to write to file stores
by means of an object associated with a read-only file system throws ReadOnlyFileSystemException.
File systems are safe for use by multiple concurrent threads. The close method may be invoked at any time to close a file system but
whether a file system is asynchronously closeable is provider specific
and therefore unspecified. In other words, if a thread is accessing an
object in a file system, and another thread invokes the close method
then it may require to block until the first operation is complete. Closing
a file system causes all open channels, watch services, and other closeable objects associated with the file system to be closed.
| Modifier | Constructor and Description |
|---|---|
protected |
FileSystem()
Initializes a new instance of this class.
|
| Modifier and Type | Method and Description |
|---|---|
abstract void |
close()
Closes this file system.
|
abstract Iterable<FileStore> |
getFileStores()
Returns an object to iterate over the underlying file stores.
|
abstract Path |
getPath(String first,
String... more)
Converts a path string, or a sequence of strings that when joined form
a path string, to a
Path. |
abstract PathMatcher |
getPathMatcher(String syntaxAndPattern)
Returns a
PathMatcher that performs match operations on the
String representation of Path objects by interpreting a
given pattern. |
abstract Iterable<Path> |
getRootDirectories()
Returns an object to iterate over the paths of the root directories.
|
abstract String |
getSeparator()
Returns the name separator, represented as a string.
|
abstract UserPrincipalLookupService |
getUserPrincipalLookupService()
Returns the
UserPrincipalLookupService for this file system
(optional operation). |
abstract boolean |
isOpen()
Tells whether or not this file system is open.
|
abstract boolean |
isReadOnly()
Tells whether or not this file system allows only read-only access to
its file stores.
|
abstract WatchService |
newWatchService()
Constructs a new
WatchService (optional operation). |
abstract FileSystemProvider |
provider()
Returns the provider that created this file system.
|
abstract Set<String> |
supportedFileAttributeViews()
Returns the set of the
names of the file
attribute views supported by this FileSystem. |
public abstract FileSystemProvider provider()
public abstract void close()
throws IOException
After a file system is closed then all subsequent access to the file
system, either by methods defined by this class or on objects associated
with this file system, throw ClosedFileSystemException. If the
file system is already closed then invoking this method has no effect.
Closing a file system will close all open channels, directory-streams,
watch-service, and other closeable objects associated
with this file system. The default file
system cannot be closed.
close in interface Closeableclose in interface AutoCloseableIOException - If an I/O error occursUnsupportedOperationException - Thrown in the case of the default file systempublic abstract boolean isOpen()
File systems created by the default provider are always open.
true if, and only if, this file system is openpublic abstract boolean isReadOnly()
true if, and only if, this file system provides
read-only accesspublic abstract String getSeparator()
The name separator is used to separate names in a path string. An
implementation may support multiple name separators in which case this
method returns an implementation specific default name separator.
This separator is used when creating path strings by invoking the toString() method.
In the case of the default provider, this method returns the same
separator as File.separator.
public abstract Iterable<Path> getRootDirectories()
A file system provides access to a file store that may be composed of a number of distinct file hierarchies, each with its own top-level root directory. Unless denied by the security manager, each element in the returned iterator corresponds to the root directory of a distinct file hierarchy. The order of the elements is not defined. The file hierarchies may change during the lifetime of the Java virtual machine. For example, in some implementations, the insertion of removable media may result in the creation of a new file hierarchy with its own top-level directory.
When a security manager is installed, it is invoked to check access
to the each root directory. If denied, the root directory is not returned
by the iterator. In the case of the default provider, the SecurityManager.checkRead(String) method is invoked to check read access
to each root directory. It is system dependent if the permission checks
are done when the iterator is obtained or during iteration.
public abstract Iterable<FileStore> getFileStores()
The elements of the returned iterator are the FileStores for this file system. The order of the elements is
not defined and the file stores may change during the lifetime of the
Java virtual machine. When an I/O error occurs, perhaps because a file
store is not accessible, then it is not returned by the iterator.
In the case of the default provider, and a security manager is
installed, the security manager is invoked to check RuntimePermission("getFileStoreAttributes"). If denied, then
no file stores are returned by the iterator. In addition, the security
manager's SecurityManager.checkRead(String) method is invoked to
check read access to the file store's top-most directory. If
denied, the file store is not returned by the iterator. It is system
dependent if the permission checks are done when the iterator is obtained
or during iteration.
Usage Example: Suppose we want to print the space usage for all file stores:
for (FileStore store: FileSystems.getDefault().getFileStores()) {
long total = store.getTotalSpace() / 1024;
long used = (store.getTotalSpace() - store.getUnallocatedSpace()) / 1024;
long avail = store.getUsableSpace() / 1024;
System.out.format("%-20s %12d %12d %12d%n", store, total, used, avail);
}
public abstract Set<String> supportedFileAttributeViews()
names of the file
attribute views supported by this FileSystem.
The BasicFileAttributeView is required to be supported and
therefore the set contains at least one element, "basic".
The supportsFileAttributeView(String) method may be used to test if an
underlying FileStore supports the file attributes identified by a
file attribute view.
public abstract Path getPath(String first, String... more)
Path. If more does not specify any
elements then the value of the first parameter is the path string
to convert. If more specifies one or more elements then each
non-empty string, including first, is considered to be a sequence
of name elements (see Path) and is joined to form a path string.
The details as to how the Strings are joined is provider specific but
typically they will be joined using the name-separator as the separator. For example, if the name separator is
"/" and getPath("/foo","bar","gus") is invoked, then the
path string "/foo/bar/gus" is converted to a Path.
A Path representing an empty path is returned if first
is the empty string and more does not contain any non-empty
strings.
The parsing and conversion to a path object is inherently
implementation dependent. In the simplest case, the path string is rejected,
and InvalidPathException thrown, if the path string contains
characters that cannot be converted to characters that are legal
to the file store. For example, on UNIX systems, the NUL (\u0000)
character is not allowed to be present in a path. An implementation may
choose to reject path strings that contain names that are longer than those
allowed by any file store, and where an implementation supports a complex
path syntax, it may choose to reject path strings that are badly
formed.
In the case of the default provider, path strings are parsed based on the definition of paths at the platform or virtual file system level. For example, an operating system may not allow specific characters to be present in a file name, but a specific underlying file store may impose different or additional restrictions on the set of legal characters.
This method throws InvalidPathException when the path string
cannot be converted to a path. Where possible, and where applicable,
the exception is created with an index value indicating the first position in the path parameter
that caused the path string to be rejected.
first - the path string or initial part of the path stringmore - additional strings to be joined to form the path stringPathInvalidPathException - If the path string cannot be convertedpublic abstract PathMatcher getPathMatcher(String syntaxAndPattern)
PathMatcher that performs match operations on the
String representation of Path objects by interpreting a
given pattern.
The syntaxAndPattern parameter identifies the syntax and the
pattern and takes the form:
wheresyntax:pattern
':' stands for itself.
A FileSystem implementation supports the "glob" and
"regex" syntaxes, and may support others. The value of the syntax
component is compared without regard to case.
When the syntax is "glob" then the String
representation of the path is matched using a limited pattern language
that resembles regular expressions but with a simpler syntax. For example:
*.javaMatches a path that represents a file name ending in .java*.*Matches file names containing a dot *.{java,class}Matches file names ending with .javaor.classfoo.?Matches file names starting with foo.and a single character extension/home/*/* Matches /home/gus/data on UNIX platforms /home/** Matches /home/gus and /home/gus/data on UNIX platforms C:\\* Matches C:\foo and C:\bar on the Windows platform (note that the backslash is escaped; as a string literal in the Java Language the pattern would be "C:\\\\*")
The following rules are used to interpret glob patterns:
The * character matches zero or more characters of a name component without
crossing directory boundaries.
The ** characters matches zero or more characters crossing directory boundaries.
The ? character matches exactly one character of a
name component.
The backslash character (\) is used to escape characters
that would otherwise be interpreted as special characters. The expression
\\ matches a single backslash and "\{" matches a left brace
for example.
The [ ] characters are a bracket expression that
match a single character of a name component out of a set of characters.
For example, [abc] matches "a", "b", or "c".
The hyphen (-) may be used to specify a range so [a-z]
specifies a range that matches from "a" to "z" (inclusive).
These forms can be mixed so [abce-g] matches "a", "b",
"c", "e", "f" or "g". If the character
after the [ is a ! then it is used for negation so [!a-c] matches any character except "a", "b", or "c".
Within a bracket expression the *, ? and \
characters match themselves. The (-) character matches itself if
it is the first character within the brackets, or the first character
after the ! if negating.
The { } characters are a group of subpatterns, where
the group matches if any subpattern in the group matches. The ","
character is used to separate the subpatterns. Groups cannot be nested.
Leading period/dot characters in file name are
treated as regular characters in match operations. For example,
the "*" glob pattern matches file name ".login".
The Files.isHidden(java.nio.file.Path) method may be used to test whether a file
is considered hidden.
All other characters match themselves in an implementation
dependent manner. This includes characters representing any name-separators.
The matching of root components is highly
implementation-dependent and is not specified.
When the syntax is "regex" then the pattern component is a
regular expression as defined by the Pattern
class.
For both the glob and regex syntaxes, the matching details, such as whether the matching is case sensitive, are implementation-dependent and therefore not specified.
syntaxAndPattern - The syntax and patternIllegalArgumentException - If the parameter does not take the form: syntax:patternPatternSyntaxException - If the pattern is invalidUnsupportedOperationException - If the pattern syntax is not known to the implementationFiles.newDirectoryStream(Path,String)public abstract UserPrincipalLookupService getUserPrincipalLookupService()
UserPrincipalLookupService for this file system
(optional operation). The resulting lookup service may be used to
lookup user or group names.
Usage Example: Suppose we want to make "joe" the owner of a file:
UserPrincipalLookupService lookupService = FileSystems.getDefault().getUserPrincipalLookupService();
Files.setOwner(path, lookupService.lookupPrincipalByName("joe"));
UserPrincipalLookupService for this file systemUnsupportedOperationException - If this FileSystem does not does have a lookup servicepublic abstract WatchService newWatchService() throws IOException
WatchService (optional operation).
This method constructs a new watch service that may be used to watch registered objects for changes and events.
UnsupportedOperationException - If this FileSystem does not support watching file system
objects for changes and events. This exception is not thrown
by FileSystems created by the default provider.IOException - If an I/O error occurs 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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